Wednesday, September 10, 2025

SPACE/COSMOS

Simulations solve centuries-old cosmic mystery – and discover new class of ancient star systems

University of Surrey

A globular cluster naturally emerges in the high-resolution EDGE simulations. — image:
A globular cluster (white concentration of stars) naturally emerges in the high resolution EDGE simulations. These simulations also predict the existence of a new class of object: globular cluster-like dwarfs. These new objects form similarly to globular clusters but in their own dark matter halo. The nearby Reticulum II dwarf galaxy may be such an object that has been hiding in plain sight in our cosmic backyard. If so, it promises unprecedented constraints on the nature of dark matter and a new place to hunt for the first metal-free stars.
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Credit: University of Surrey, Matt Orkney, Andrew Pontzen & Ethan Taylor

For centuries, astronomers have puzzled over the origins of one of the universe’s oldest and densest stellar systems, known as globular clusters. Now, a University of Surrey-led study published in Nature has finally solved the mystery using detailed simulations – while also uncovering a new class of object that could already be in our own galaxy.

Globular clusters are dense collections of hundreds of thousands to millions of stars found orbiting around galaxies, including the Milky Way. Unlike galaxies, they show no evidence of dark matter, and their stars are unusually uniform in age and chemical composition – traits that have left scientists debating their formation since their discovery in the 17th century.

Surrey researchers used ultra-high-resolution simulations that can trace the Universe’s 13.8-billion-year history in unprecedented detail, allowing them to watch globular clusters form in real-time within their virtual cosmos, called EDGE. The simulations find multiple pathways for their creation and, unexpectedly, the emergence of a new class of star system – “globular cluster-like dwarfs” – that sits between globular clusters and dwarf galaxies in terms of their properties.

Dr Ethan Taylor, Postdoctoral Research Associate at the University of Surrey’s School of Mathematics and Physics and lead author of the study, said:

“The formation of globular clusters has been a mystery for hundreds of years, so being able to add additional context surrounding how they form is amazing. We were able to do this in our EDGE simulations without having to add anything special to make them appear, and it just brings the simulations that extra level of realism. Additionally, being able to find a new class of object in the simulations is very exciting, especially since we have already identified a handful of candidates which exist in our very own Milky Way.”

Working in collaboration with Durham University, the University of Bath, the University of Hertfordshire, Carnegie Observatories and the American Museum of Natural History in the USA, Lund University in Sweden and the University of Barcelona in Spain, researchers used the UK’s DiRAC National Supercomputer facility to run the EDGE simulations over several years. To put the scale into perspective, if the largest simulations were run on a standard or high-end laptop, they would take decades to complete. These simulations not only recreated realistic globular clusters and dwarf galaxies but also predicted a previously unknown class of object.

Conventional dwarf galaxies are typically dominated by dark matter, with around a thousand times more of the mysterious substance than stars and gas combined. However, the newly identified ‘globular cluster-like dwarfs’ appear similar to regular star clusters when observed, yet still contain a significant amount of dark matter – meaning telescopes may have already found them in the real universe and classified them as regular globular clusters. This small difference would place them in a unique position to study both dark matter and cluster formation.

Several known Milky Way satellites, such as the “ultra-faint” dwarf galaxy Reticulum II, are likely candidates. If confirmed, they could become prime sites for the search for pristine, metal-free stars born in the early Universe and new locations to test models for the ever-elusive “dark matter”.

Professor Justin Read, Chair of Astrophysics at the University of Surrey, said:

“The EDGE project set out to build the most realistic simulation of the very smallest galaxies in the Universe – one that could follow all 13.8 billion years of its history while still zooming in on the tiny details, like the blast from a single exploding star. It took years to run on the UK’s DiRAC National Supercomputer, but the payoff has been extraordinary. At a resolution of just 10 light years, fine enough to capture the effects of individual supernovae, we’ve been able to show that globular clusters can form in at least two different ways, both without dark matter.”

The next step is to confirm the existence of these globular cluster-like dwarfs through targeted observations with telescopes, including the James Webb Space Telescope and upcoming deep spectroscopic surveys. If they do, it could give astronomers new ways to test dark matter theories and offer some of the best chances to find the Universe’s very first generation of “metal-free” stars.

[ENDS]

Notes to editors

Dr Ethan Taylor and Professor Justin Read are available for interview; please contact mediarelations@surrey.ac.uk to arrange.

Once published, the full paper can be found at https://www.nature.com/articles/s41586-025-09494-x (10.1038/s41586-025-09494-x)
An image can be found here. Credit: University of Surrey, Matt Orkney, Andrew Pontzen & Ethan Taylor - Caption: A globular cluster (white concentration of stars) naturally emerges in the high-resolution EDGE simulations. These simulations also predict the existence of a new class of object: globular cluster-like dwarfs. These new objects form similarly to globular clusters, but in their own dark matter halo. The nearby Reticulum II dwarf galaxy may be such an object that has been hiding in plain sight in our cosmic backyard. If so, it promises unprecedented constraints on the nature of dark matter and a new place to hunt for the first metal-free stars.
Videos from the simulations can be found at https://dirac.ac.uk/featured-project-edge-project/. For access to video files, please contact mediarelations@surrey.ac.uk

Infografic showcasing the advancements of gravitational wave observatories -- among the most precise measuring machines ever built by humankind -- in observing black holes cosmic collisions, with the registered signals shown in the bottom panel. These events are embedded in a multitude of celestial objects, which modern telescopes are also observing with ever increasing precision, producing the beautiful images displayed in the top panel.

Credit

Dr. Derek Davis (Caltech, LIGO Laboratory).

Artistic representation of a ringing rotating black hole.

Credit

Aurore Simonnet (SSU/EdEon).

Journal

Nature

DOI

10.1038/s41586-025-09494-x

Article Publication Date

10-Sep-2025

Ten years after the discovery, gravitational waves verify Stephen Hawking's Black Hole Area Theorem

European Gravitational Observatory

A Cosmic Symphony Revealed — image:
This artwork imagines the ultimate front-row seat for GW250114, a powerful collision between two black holes observed in gravitational waves by the US National Science Foundation LIGO. It depicts the view from one of the black holes as it spirals toward its cosmic partner. Ten years after LIGO's landmark detection of gravitational waves, the observatory's improved detectors allowed it to "hear" this celestial collision with unprecedented clarity. The gravitational-wave data enabled scientists to distinguish multiple subtle tones ringing out like a cosmic bell across the universe (imagined here as intertwining musical threads spiraling toward the center).
Though only LIGO was online during GW250114, it now routinely operates as part of a network with other gravitational-wave detectors, including Europe's Virgo and Japan's KAGRA.
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Credit: Aurore Simonnet (SSU/EdEon)/LVK/URI

On September 14, 2015, a signal arrived on Earth, carrying information about a pair of remote black holes that had spiraled together and merged. The signal had traveled about 1.3 billion years to reach us at the speed of light—but it was not made of light. It was a different kind of signal: a quivering of space-time called gravitational waves, first predicted by Albert Einstein 100 years prior. On that day 10 years ago, the twin detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) made the first-ever direct detection of gravitational waves. The LIGO and Virgo collaborations announced it to the world in February 2016, after six months of analysis and verification.

The historic discovery meant that researchers could now sense the universe through three different means. Light waves, such as X-rays, optical, radio, and other wavelengths of light, as well as high-energy particles called cosmic rays and neutrinos had been captured before, but this was the first time researchers had witnessed a cosmic event through its gravitational warping of space-time. For this achievement, first dreamed up more than 40 years prior, three of the LIGO founders won the 2017 Nobel Prize in Physics: MIT's Rainer Weiss, professor of physics, emeritus (who recently passed away at age 92); Caltech's Barry Barish; and Caltech's Kip Thorne.

LIGO, which consists of detectors in both Hanford, Washington and Livingston, Louisiana, the Virgo detector in Italy and KAGRA in Japan operate in coordination and currently are routinely observing roughly one black hole merger every three days. Together, the gravitational-wave-hunting network, known as LVK (LIGO, Virgo, KAGRA), has captured a total of more than 300 black hole mergers, most of which are already confirmed while others await further analysis. During the network's current science run, the fourth since the first run in 2015, the LVK has discovered about 230 candidate black hole mergers, more than doubling the number caught in the first three runs.

The dramatic rise in the number of LVK discoveries over the past decade is owed to several improvements to their detectors—some of which involve cutting-edge quantum precision engineering. These gravitational-wave interferometers remain by far the most precise rulers for making measurements ever created by humans. The space-time distortions induced by gravitational waves are incredibly minuscule. To sense them, LIGO and Virgo must detect changes in space-time smaller than 1/10,000 the width of a proton. That's 700 trillion times smaller than the width of a human hair.

The Clearest Signal Yet

The improved sensitivity of the instruments is exemplified in a recent discovery of a black hole merger referred to as GW250114 (the numbers denote the date the gravitational-wave signal arrived at Earth: January 14, 2025). The event was not that different from the first-ever detection (called GW150914)—both involve colliding black holes about 1.3 billion light-years away with masses between 30 to 40 times that of our Sun. But thanks to 10 years of technological advances reducing instrumental noise, the GW250114 signal is dramatically clearer.

"We can hear it loud and clear, and that lets us test the fundamental laws of physics," says LIGO team member Katerina Chatziioannou, Caltech assistant professor of physics and William H. Hurt Scholar, and one of the leading authors of a new study on GW250114 published in the Physical Review Letters.

By analyzing the frequencies of gravitational waves emitted by the merger, the LVK team was able to provide the best observational evidence captured to date for what is known as the black hole area theorem, an idea put forth by Stephen Hawking in 1971 that says the total surface areas of black holes cannot decrease. When black holes merge, their masses combine, increasing the surface area. But they also lose energy in the form of gravitational waves during the phenomenon. Additionally, the merger can cause the combined black hole to increase its spin, which leads to it having a smaller area. The black hole area theorem states that, despite these competing factors, the total surface area must grow in size.

Later, Hawking and physicist Jacob Bekenstein concluded that a black hole's area is proportional to its entropy, or degree of disorder. The findings paved the way for later groundbreaking work in the field of quantum gravity, which attempts to unite two pillars of modern physics: general relativity and quantum physics.

In essence, the detection (made just by LIGO, since Virgo was undergoing routine maintenance and KAGRA was offline during this particular observation) allowed the team to "hear" two black holes growing as they merged into one, verifying Hawking's theorem. The initial black holes had a total surface area of 240,000 square kilometers (roughly the size of United Kingdom), while the final area was about 400,000 square kilometers (almost the size of Sweden)—a clear increase. This is the second test of the black hole area theorem; an initial test was performed in 2021 using data from the first GW150914 signal, but because that data was not as clean, the results had a confidence level of 95 percent as compared to 99.999 percent for the new data.
Kip Thorne recalls Hawking phoning him to ask whether LIGO might be able to test his theorem immediately after he learned of the 2015 gravitational-wave detection. Hawking died in 2018 and sadly did not live to see his theory observationally verified. "If Hawking were alive, he would have reveled in seeing the area of the merged black holes increase," Thorne says.

The trickiest part of this type of analysis had to do with determining the final surface area of the merged black hole. The surface areas of pre-merger black holes can be more readily gleaned as the pair spiral together, roiling space-time and producing gravitational waves. But after the black holes merge, the signal is not as clearcut. During this so-called ringdown phase, the final black hole vibrates like a struck bell.
In the new study, the researchers were able to precisely measure the details of the ringdown phase, which allowed them to calculate the mass and spin of the black hole, and subsequently determine its surface area. More precisely, they were able, for the first time, to confidently pick out two distinct gravitational-wave modes in the ringdown phase. The modes are like characteristic sounds a bell would make when struck; they have somewhat similar frequencies but die out at different rates, which makes them hard to identify. The improved data for GW250114 meant that the team could extract the modes, demonstrating that the black hole's ringdown occurred exactly as predicted by math models
Another study from the LVK, submitted to Physical Review Letters today, places limits on a predicted third, higher-pitch tone in the GW250114 signal, and performs some of the most stringent tests yet of general relativity's accuracy in describing merging black holes.

“Analyzing strain data from the detectors to detect transient astrophysical signals, send out alerts to trigger follow-up observations from telescopes or publish physics results gathering information from up to hundreds of events is quite a long journey - adds Nicolas Arnaud, CNRS researcher in France and Virgo coordinator of the fourth science run - Out of the many skilled steps that such a complex framework requires, I see the humans behind all these data, in particular those who are on duty at any time, watching over our instruments. There are LVK scientists in all regions, pursuing a common goal: literally, the Sun never goes down above our collaborations!”

Pushing the limits

LIGO and Virgo have also unveiled neutron stars over the past decade. Like black holes, neutron stars form the explosive deaths of massive stars, but they weigh less and glow with light. Of note, in August of 2017, LIGO and Virgo witnessed an epic collision between a pair of neutron stars—a kilonova—that sent gold and other heavy elements flying into space and drew the gaze of dozens of telescopes around the world, which captured light ranging from high-energy gamma rays to low-energy radio waves. The "multi-messenger" astronomy event marked the first time that both light and gravitational waves had been captured in a single cosmic event. Today, the LVK continues to alert the astronomical community to potential neutron star collisions, who then use telescopes to search the skies for signs of another kilonova.

"The global LVK network is essential to gravitational-wave astronomy," says Gianluca Gemme, Virgo spokesperson and director of research at INFN (Istituto Nazionale di Fisica Nucleare). "With three or more detectors operating in unison, we can pinpoint cosmic events with greater accuracy, extract richer astrophysical information, and enable rapid alerts for multi-messenger follow-up. Virgo is proud to contribute to this worldwide scientific endeavor."

Other LVK scientific discoveries include the first detection of collisions between one neutron star and one black hole; asymmetrical mergers, in which one black hole is significantly more massive than its partner neutron star; the discovery of the lightest black holes known, challenging the idea that there is a "mass gap" between neutron stars and black holes; and the most massive black hole merger seen yet with a merged mass of 225 solar masses. For reference, the previous record-holder for the most massive merger had a combined mass of 140 solar masses.

In the coming years, the scientists of LVK hope to further fine tune their machines, expanding their reach deeper and deeper into space. They also plan to use the knowledge they have gained to build another gravitational-wave detector, LIGO India. Looking farther into the future, scientists are working on a concept for even larger detectors.The European project, called Einstein Telescope, plans to build one or two huge underground interferometers with arms of more than 10 kilometers, The US one, called Cosmic Explorer, would be similar to the current LIGO but with arms 40 kilometers long. Observatories on this scale would allow scientists to hear the earliest black hole mergers in the universe and, possibly, the echo of the gravitational shakes of the very first moments of our universe.

“This is an amazing time for gravitational wave research: thanks to instruments such as Virgo, LIGO and KAGRA, we can explore a dark universe that was previously completely inaccessible. - said Massimo Carpinelli, professor at University of Milano Bicocca and director of the European Gravitational Observatory in Cascina - The scientific achievements of these 10 years are triggering a real revolution in our view of the Universe. We are already preparing a new generation of detectors such as the Einstein Telescope in Europe and Cosmic Explorer in the US, as well as the LISA space interferometer, which will take us even further into space and back in time. In the coming years, we will certainly be able to tackle these extraordinary challenges thanks to increasingly broad and solid cooperation between scientists, different countries and institutions, both at European and global level.”

The LIGO-Virgo-KAGRA Collaboration

LIGO is funded by the NSF and operated by Caltech and MIT, which together conceived and built the project. Financial support for the Advanced LIGO project was led by the NSF with Germany (Max Planck Society), the United Kingdom (Science and Technology Facilities Council), and Australia (Australian Research Council) making significant commitments and contributions to the project. More than 1,600 scientists from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration. Additional partners are listed at my.ligo.org/census.php.

The Virgo Collaboration is currently composed of approximately 1.000 members from 175 institutions in 20 different (mainly European) countries. The European Gravitational Observatory (EGO) hosts the Virgo detector near Pisa in Italy, and is funded by Centre National de la Recherche Scientifique (CNRS) in France, the National Institute of Nuclear Physics (INFN) in Italy, the National Institute of Subatomic Physics (Nikhef) in the Netherlands, The Research Foundation – Flanders (FWO) and the Belgian Fund for Scientific Research (F.R.S.–FNRS). A list of the Virgo Collaboration groups can be found at: https://www.virgo-gw.eu/about/scientific-collaboration/ More information is available on the Virgo website at https://www.virgo-gw.eu

KAGRA is the laser interferometer with 3-kilometer arm length in Kamioka, Gifu, Japan. The host institute is the Institute for Cosmic Ray Research (ICRR), the University of Tokyo, and the project is co-hosted by National Astronomical Observatory of Japan (NAOJ) and High Energy Accelerator Research Organization (KEK). KAGRA collaboration is composed of more than 400 members from 128 institutes in 17 countries/regions. KAGRA's information for general audiences is at the website gwcenter.icrr.u-tokyo.ac.jp/en/. Resources for researchers are accessible from gwwiki.icrr.u-tokyo.ac.jp/JGWwiki/KAGRA.

Clear Signal Sheds Light on Black Holes - Infographic

Credit

Lucy Reading-Ikkanda/Simons Foundation

This chart plots discoveries made by the LIGO-Virgo-KAGRA (LVK) network since LIGO's first detection, in 2015, of gravitational waves emanating from a pair of colliding black holes. The detections consist mainly of black hole mergers, but a handful involve neutron stars (either black hole-neutron star collisions or neutron star-neutron star collisions).

So far, during the current, fourth science run, the LVK detectors have spotted about 220 mergers, which more than doubles the number (90) found in the first three runs combined. The closest event observed to date, shown in Run 2 and indicated by the down arrow, is a binary neutron star merger known as GW170817, located only 0.13 gigalight-years away (or 130 million light-years).

In this chart, the total masses of the initial objects are represented by size, while the signal strength is indicated by color. The plot demonstrates that over time the gravitational-wave observatories are both finding more black holes and detecting them with higher signal-to-noise ratios, thanks to cutting-edge advancements made to the detectors.

Note that the black hole detections in the latter half of the fourth run are grey and appear to be the same size because these data have not been released in full—with the exception of the event called GW250114. That event, the clearest signal heard by LIGO yet, appears as a bright, orange dot on the chart in the fourth run.

Credit

LIGO/Caltech/MIT/R. Hurt (IPAC)

The Clearest of Chirps [VIDEO]

This video compares a newly detected gravitational-wave signal called GW250114 with the first gravitational-wave signal ever detected, GW150914, in 2015. Both signals came from colliding black holes, each between 30 to 40 times the mass of the Sun. The colorful visuals illustrate how each gravitational wave’s frequency increases over time as the two black holes spiral closer together, producing a pattern scientists call a “chirp.” Brighter colors indicate that the signal was more clearly identified by LIGO above the background noise. The same gravitational-wave data has also been converted into audio frequencies, making it possible to actually hear these cosmic collisions as they happen.

The video plays each detection twice. The first round is played at the original frequencies, in which the gravitational-wave frequencies have been converted directly into sound waves. In the second round, the pitch has been increased by 30 percent to make the chirp easier to hear.

Listen for the low “whoosh” rising out of the background static—that's the sound of space-time itself rippling. Notice how much quieter the background noise is behind GW250114 compared to GW150914, an indication of how dramatically LIGO’s sensitivity has improved over the past decade.

Credit

LIGO/Derek Davis (URI)

Clearer View of Black Hole Merger [VIDEO] |

A numerical relativity simulation of the recently observed GW250114 event, a binary black hole merger detected by LIGO on January 14, 2025. The blue and white surface shows a two- dimensional slice of the gravitational waves spiraling outward as the black holes orbit one another. Throughout this inspiral, the gravitational waves grow in magnitude, peaking as the black holes merge, and then decreasing rapidly as the newly formed remnant black hole settles.

The observed gravitational-wave signal from GW250114 is shown below in white. In comparison, the gray line shows much noisier data from LIGO's first gravitational-wave observation, GW150914. While the amplitudes of these signals are comparable, significant improvements in detector sensitivity over the past decade have vastly reduced the amount of noise present in GW250114 relative to GW150914.\

YouTube link: https://youtu.be/hnzWNkjKkPU

Credit

Deborah Ferguson, Derek Davis, Rob Coyne (URI) / LIGO / MAYA Collaboration. Simulation performed with NSF's TACC Frontera supercomputer.

Journal

Physical Review Letters

DOI

10.1103/kw5g-d732

Article Title

GW250114: testing Hawking’s area law and the Kerr nature of black holes

Article Publication Date

10-Sep-2025

Hawking and Kerr black hole theories confirmed by gravitational wave

University of Birmingham

image:
Left panel: Frequency and decay time (half-life) of the different ringdown tones measured in GW250114. The black markers indicate the values predicted for a Kerr black hole. Right panel: gravitational-wave signal (bottom spiral) emitted by the remnant black hole (bottom sphere) into the different tones, for a numerical simulation matching the measured parameters of GW250114.
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Credit: Dr. Keefe Mitman (Cornell University), Prof. Harald Pfeiffer (Albert Einstein Institute, Potsdam).

Scientists have confirmed two long-standing theories relating to black holes – thanks to the detection of the most clearly recorded gravitational wave signal to date.

Ten years after detecting the first gravitational wave, the LIGO-Virgo-KAGRA Collaboration has today (10 Sep) announced the detection of GW250114 – a ripple in spacetime which offers unprecedented insights into the nature of black holes and the fundamental laws of physics.

The study confirms Professor Stephen Hawking’s 1971 prediction that when black holes collide, the total event horizon area of the resulting black hole is bigger than the sum of individual black holes - it cannot shrink.

Research also confirmed the Kerr nature of black holes - a set of equations developed in 1963 by New Zealand mathematician Roy Kerr elegantly explaining what space and time look like near a spinning black hole. The Kerr metric predicts effects such as space being ‘dragged’ around and light looping to make multiple copies of objects.

Publishing their findings in Physical Review Letters, the international group of researchers – including experts from the University of Birmingham – note that GW250114 was detected with a signal-to-noise ratio of 80. This clarity enabled precise tests of general relativity and black hole thermodynamics.

Geraint Pratten, Royal Society University Fellow at the University of Birmingham and member of the LVK paper writing team commented: “GW250114 is the loudest gravitational wave event we have detected to date, it was like a whisper becoming a shout. This gave us an unprecedented opportunity to put Einstein's theories through some of the most rigorous tests possible - validating one of Stephen Hawking's pioneering predictions that when black holes merge, the combined area of their event horizons can only grow, never shrink.”

GW250114 was picked up by the twin detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the USA. LIGO operates in coordination with two international partners, the Virgo gravitational-wave detector in Italy and KAGRA in Japan forming a gravitational-wave-hunting network, known as the LVK (LIGO, Virgo, KAGRA).

The LVK team, which includes members of the University of Birmingham, was able to establish that GW250114 was generated by the collision of two black holes with masses of about 32 times that of our Sun.

LIGO detects a gravitational wave passing through the Earth every few days, but GW250114, has turned out to be special. The data show that the initial black holes had a total surface area roughly the size of the United Kingdom (240,000 square kilometers) while the final area was about 400,000 square kilometers (roughly the size of Sweden).

In the 1970s, Hawking and physicist Jacob Bekenstein concluded that the black hole's area is proportional to its entropy, or degree of disorder, paving the way for later groundbreaking work in the field of quantum gravity, which attempts to unite two pillars of modern physics: general relativity and quantum physics.

After the black holes fused together, during what physicists call the ringdown phase, the final black hole vibrates emitting gravitational waves at specific frequencies, like characteristic sounds a bell would make when struck, the ‘voices’ of the black hole.

Roy Kerr’s solution predicts that a black hole, and its ‘voices’ when disturbed, are uniquely described just by two numbers: the mass and the spin of a black hole. The implications of this groundbreaking result single out black holes from any other celestial objects: a star can only be described by a very large set of complex properties, while even black holes heavier than a million times our Sun are astonishingly described just by two simple numbers, mass and spin.

Gregorio Carullo, Assistant Professor at the University of Birmingham and coordinator of one of the LVK analysis teams commented: “Given the clarity of the signal produced by GW250114, for the first time we could pick out two ‘tones’ from the black hole voices and confirm that they behave according to Kerr’s prediction, obtaining unprecedented solid evidence for the Kerr nature of black holes found in nature.”

The results are released almost exactly ten years after the first landmark observation of gravitational waves. On September 14, 2015, a signal arrived on Earth, carrying information about a pair of remote black holes that had spiralled and fused together.

This historic discovery, to which Birmingham’s researchers have made wide-ranging contributions by developing hardware for the LIGO detectors, highly accurate models of gravitational waves generated by merging black holes, and analysis techniques to tease out from the data the properties of black holes, meant that scientists could now sense the universe through three different means.

Patricia Schmidt, Associate Professor at the University of Birmingham and co-chair of LVK analysis team, commented: “The detection of a black hole binary with parameters similar to those of GW150914, but three times louder, only a decade after the breakthrough discovery is owed to the tremendous technological improvements of our instruments, paving the path for precision astronomy with gravitational waves.“

Amit Singh Ubhi, part of the Birmingham’s instrumentation team contributing key hardware that made such discovery possible, added: “The exceptional signal-to-noise ratio of GW250114 showcases the collective advances in gravitational-wave instrumentation across our community. This unprecedented clarity allows us to probe black hole evolution with unmatched precision, showcasing the impact of cutting-edge technology on our understanding of the fundamental laws of nature.”

ENDS

For more information, interviews or an embargoed copy of the paper, please contact the University of Birmingham press office on pressoffice@contacts.bham.ac.uk or +44 (0) 121 414 2772.

Image captions and credits

Left panel: Frequency and decay time (half-life) of the different ringdown tones measured in GW250114. The black markers indicate the values predicted for a Kerr black hole. Right panel: gravitational-wave signal (bottom spiral) emitted by the remnant black hole (bottom sphere) into the different tones, for a numerical simulation matching the measured parameters of GW250114. Credits: Dr. Keefe Mitman (Cornell University), Prof. Harald Pfeiffer (Albert Einstein Institute, Potsdam).
Infografic showcasing the advancements of gravitational wave observatories -- among the most precise measuring machines ever built by humankind -- in observing black holes cosmic collisions, with the registered signals shown in the bottom panel. These events are embedded in a multitude of celestial objects, which modern telescopes are also observing with ever increasing precision, producing the beautiful images displayed in the top panel. Credits: Dr. Derek Davis (Caltech, LIGO Laboratory).
Artistic representation of a ringing rotating black hole. Credits: Aurore Simonnet (SSU/EdEon).

Notes to Editors

The University of Birmingham is ranked amongst the world’s top 100 institutions, its work brings people from across the world to Birmingham, including researchers and teachers and more than 8,000 international students from over 150 countries.
'GW250114: testing Hawking’s area law and the Kerr nature of black holes' - A.G.Abac, et al is published by Physical Review Letters.
Participating UK institutions include: University of Birmingham; University of Warwick; Queen Mary University of London; Cardiff University; University of Strathclyde; Royal Holloway; King’s College London; University of Portsmouth; University of Glasgow; University of the West of Scotland; University of Southampton; University of Cambridge; University of Lancaster; and Rutherford Appleton Laboratory, Didcot

Journal

Physical Review Letters

Method of Research

Data/statistical analysis

Subject of Research

Not applicable

Article Title

'GW250114: testing Hawking’s area law and the Kerr nature of black holes

Article Publication Date

10-Sep-2025

Clearest signal yet from colliding black holes yields most precise confirmation of Hawking’s area theorem

The merged black hole rang out in spacetime as it settled post-collision, offering clues about the remnant’ s structure and properties.

American Physical Society

In a new study published in Physical Review Letters, the LIGO–Virgo–KAGRA Collaboration has used the sharpest to date gravitational wave signal from two merging black holes to precisely test Hawking’s area theorem and the remnant black hole’s nature. The paper describes GW250114, a signal captured by LIGO during its current observing run in early 2025 — almost ten years after it detected a disturbance from a similar merger for the first time in history. This time, the detectors were nearly four times as sensitive.

“This specific collision involved two black holes that looked pretty much identical to the first two we saw,” said Maximiliano Isi, assistant professor at Columbia University, associate research scientist at the Flatiron Institute, and coauthor of the study. Both mergers were of black holes about 30 times the mass of the sun. “Intrinsically, the signal is equally loud, but our detectors are just so much more high fidelity now.”

Isi led a 2021 study that used the 2015 signal to test Hawking’s area theorem with a similar technique: splicing it to isolate certain frequencies, or tones. Isi and colleagues identified the tones associated with the remnant, which allowed them to infer the area of its event horizon — the region of the black hole where no light can escape — showing that it was possible to test Hawking’s prediction. But the poorer signal limited their analyses.

With GW250114, a clearer signal with improved instrumentation allowed the authors to isolate the “ringing” in spacetime that emanated from the remnant as it settled. “The ringdown is what happens when a black hole is perturbed, just as a bell rings when you strike it,” said Katerina Chatziioannou, assistant professor at Caltech and coauthor. By “hearing” the modes in the ringdown, the team worked out the properties of the black hole and confirmed that they were consistent with the Kerr metric — an exact solution to Einstein’s field equations of general relativity for a rotating black hole, described by mathematician Roy Kerr over 60 years ago. "Two black holes with the same mass and spin are mathematically identical,” said Isi.
“It's very unique to black holes.”

The ringdown also confirmed that the remnant’s surface area increased, as Hawking predicted in 1971. “Even though it's a very simple statement,
‘areas can only increase,’ it has immense implications,” said Isi. Hawking’s theorem — the second law of black hole mechanics — mirrors the second law of thermodynamics, which says that entropy, or disorder, can only increase. The theorem led to the realization that black holes are thermodynamic objects, a paradigm shift cemented by Hawking's discovery that they have entropy and emit radiation due to quantum eﬀects near the event horizon.
“It tells us that general relativity knows something about the quantum nature of these objects and that the information, or entropy, contained in a black hole is proportional to its area,” Isi added.

The discovery follows a series of recent upgrades to improve LIGO’s sensitivity and range. "Ten years ago, we were observing signals about once per month,” said Chatziioannou. “Today, we are observing signals about once every three days.” As the technology continues to improve, scientists will obtain even crisper signals of these ripples in spacetime — and from them, a better understanding of the universe.

“This is really important as a tool in astrophysics and cosmology,” said Robert Wald, a theoretical physicist and professor at the University of Chicago who contributed to the study. “The observatory, I think, is the key thing.”

# # #

The American Physical Society is a nonprofit membership organization working to advance physics by fostering a vibrant, inclusive, and global community dedicated to science and society. APS represents more than 50,000 members, including physicists in academia, national laboratories, and industry in the United States and around the world.

Journal

Physical Review Letters

DOI

10.1103/kw5g-d732

Method of Research

Observational study

Article Title

GW250114: Testing Hawking’s Area Law and the Kerr Nature of Black Holes

Article Publication Date

10-Sep-2025

Ringing black hole confirms Einstein and Hawking’s predictions

New observations of a merger of two black holes confirm decades-old predictions by Albert Einstein, Stephen Hawking and Roy Kerr

Simons Foundation

Black Hole Merger Illustration — image:
When two black holes collide and merge, they release gravitational waves. These waves can be detected by sensitive instruments on Earth, allowing scientists to determine the mass and spin of the black holes. The clearest black hole merger signal yet, named GW250114 and recorded by LIGO in January 2025, offers new insights into these mysterious objects.
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Credit: Maggie Chiang for Simons Foundation

A decade ago, scientists first detected ripples in the fabric of space-time, called gravitational waves, from the collision of two black holes. Now, thanks to improved technology and a bit of luck, a newly detected black hole merger is providing the clearest evidence yet of how black holes work — and, in the process, offering long-sought confirmation of fundamental predictions by Albert Einstein and Stephen Hawking.

The new measurements were made by the Laser Interferometer Gravitational-Wave Observatory (LIGO), with analyses led by astrophysicists Maximiliano Isi and Will Farr of the Flatiron Institute’s Center for Computational Astrophysics in New York City. The results reveal insights into the properties of black holes and the fundamental nature of space-time, hinting at how quantum physics and Einstein’s general relativity fit together.

“This is the clearest view yet of the nature of black holes,” says Isi, who is also an assistant professor at Columbia University. “We’ve found some of the strongest evidence yet that astrophysical black holes are the black holes predicted from Albert Einstein’s theory of general relativity.”

The results were reported in a paper published September 10 in Physical Review Letters by the LIGO-Virgo-KAGRA Collaboration.

For massive stars, black holes are the final stage in their evolution. Black holes are so dense that even light cannot escape their gravity. When two black holes collide, the event distorts space itself, creating ripples in space-time that fan out across the universe, like sound waves ringing out from a struck bell.

Those space-deforming ripples, called gravitational waves, can tell scientists a great deal about the objects that created them. Just as a large iron bell makes different sounds than a smaller aluminum bell, the “sound” a black hole merger makes is specific to the properties of the black holes involved.

Scientists can detect gravitational waves with special instruments at observatories such as LIGO in the United States, Virgo in Italy and KAGRA in Japan. These instruments carefully measure how long it takes a laser to travel a given path. As gravitational waves stretch and compress space-time, the length of the instrument, and thus the light’s travel time, changes minutely. By measuring those tiny changes with great precision, scientists can use them to determine the black holes’ characteristics.

The newly reported gravitational waves were found to be created by a merger that formed a black hole with the mass of 63 suns and spinning at 100 revolutions per second. The findings come 10 years after LIGO made the first black hole merger detection. Since that landmark discovery, improvements in equipment and techniques have enabled scientists to get a much clearer look at these space-shaking events.

“The new pair of black holes are almost twins to the historic first detection in 2015,” Isi says. “But the instruments are much better, so we’re able to analyze the signal in ways that just weren't possible 10 years ago.”

With these new signals, Isi and his colleagues got a complete look at the collision from the moment the black holes first careened into each other until the final reverberations as the merged black hole settled into its new state, which happened only milliseconds after first contact.

Previously, the final reverberations were difficult to capture, as by that point, the ringing of the black hole would be very faint. As a result, scientists couldn’t separate the ringing of the collision from that of the final black hole itself.

In 2021, Isi led a study showcasing a cutting-edge method that he, Farr and others developed to isolate certain frequencies — or ‘tones’ — using data from the 2015 black hole merger. This method proved powerful, but the 2015 measurements weren’t clear enough to confirm key predictions about black holes. With the new, more precise measurements, though, Isi and his colleagues were more confident they had successfully isolated the milliseconds-long signal of the final, settled black hole. This enabled more unambiguous tests of the nature of black holes.

“Ten milliseconds sounds really short, but our instruments are so much better now that this is enough time for us to really analyze the ringing of the final black hole,” Isi says. “With this new detection, we have an exquisitely detailed view of the signal both before and after the black hole merger.”

The new observations allowed scientists to test a key conjecture dating back decades that black holes are fundamentally simple objects. In 1963, physicist Roy Kerr used Einstein’s general relativity to mathematically describe black holes with one equation. The equation showed that astrophysical black holes can be described by just two characteristics: spin and mass. With the new, higher-quality data, the scientists were able to measure the frequency and duration of the ringing of the merged black hole more precisely than ever before. This allowed them to see that, indeed, the merged black hole is a simple object, described by just its mass and spin.

The observations were also used to test a foundational idea proposed by Stephen Hawking called Hawking’s area theorem. It states that the size of a black hole’s event horizon — the line past which nothing, not even light, can return — can only ever grow. Testing whether this theorem applies requires exceptional measurements of black holes before and after their merger. Following the first black hole merger detection in 2015, Hawking wondered if the merger signature could be used to confirm his theorem. At the time, no one thought it was possible.

By 2019, a year after Hawking’s death, methods had improved enough that a first tentative confirmation came using techniques developed by Isi, Farr, and colleagues. With four times better resolution, the new data gives scientists much more confidence that Hawking’s theorem is correct.

In confirming Hawking’s theorem, the results also hint at connections to the second law of thermodynamics. This law states that a property that measures a system’s disorder, known as entropy, must increase, or at least remain constant, over time. Understanding the thermodynamics of black holes could lead to advances in other areas of physics, including quantum gravity, which aims to merge general relativity with quantum physics.

“It’s really profound that the size of a black hole’s event horizon behaves like entropy,” Isi says. “It has very deep theoretical implications and means that some aspects of black holes can be used to mathematically probe the true nature of space and time.”

Many suspect that future black hole merger detections will only reveal more about the nature of these objects. In the next decade, detectors are expected to become 10 times more sensitive than today, allowing for more rigorous tests of black hole characteristics.

“Listening to the tones emitted by these black holes is our best hope for learning about the properties of the extreme space-times they produce,” says Farr, who is also a professor at Stony Brook University. “And as we build more and better gravitational wave detectors, the precision will continue to improve.”

“For so long this field has been pure mathematical and theoretical speculation,” Isi says. “But now we’re in a position of actually seeing these amazing processes in action, which highlights how much progress there’s been — and will continue to be — in this field.”

Journal

Physical Review Letters

DOI

10.1103/kw5g-d732

Subject of Research

Not applicable

Article Publication Date

10-Sep-2025

A fleeting secondary tone was detected in the recent gravitational wave signal, offering a rare chance to test the Kerr solution, which describes a rotating black hole using only mass and spin. Excitingly, the mass and spin values from this overtone matched those from the fundamental tone. If they had differed, it would imply that additional properties are necessary to describe a black hole, but a match confirms that — at least for this black hole — no other details are needed.

Credit

Simons Foundation

An unprecedented view of merging black holes

Columbia University

Ten years after scientists first detected gravitational waves emerging from two colliding black holes, the LIGO-Virgo-KAGRA collaboration, a research team that includes Columbia astronomy professor Maximiliano Isi, has recorded a signal from a nearly identical black hole collision. Improvements in the detection technology allowed the researchers to see the black holes almost four times as clearly as they could a decade ago, and to confirm two important predictions: That merging black holes only ever grow or remain stable in size—as the late physicist Stephen Hawking predicted—and that, when disturbed, they ring like a bell, as predicted by Albert Einstein’s theory of general relativity.

“This unprecedentedly clear signal of the black hole merger known as GW250114 puts to the test some of our most important conjectures about black holes and gravitational waves,” Isi said.

In 1971, Stephen Hawking predicted that a black hole’s event horizon—its outer boundary, beyond which nothing, including light, can escape—could never decrease in size.

In 2021, using data from the gravitational wave detector LIGO, Isi and his collaborators studied gravitational waves—high-energy ripples in the fabric of space-time—emitted by the collision of two merging black holes to observationally confirm Hawking’s theory. The New York Times wrote at the time that if Isi’s confirmation had arrived before Hawking passed away, it may have helped him earn the Nobel Prize.

The new results confirm this earlier result with much higher precision, offering further evidence that the surface area of a merged black hole is never less than the sum of the two initial black holes that created it. The new paper was able to achieve this unprecedented precision by using data from both LIGO detectors, one of which is located in Washington state and the other of which is in Louisiana.

The researchers were also able to isolate and analyze the gravitational waves emitted by the black holes after they merged. By measuring the waves’ pitch and duration, they were able to learn more details about the merged black hole’s structure and properties. (The process works in much the same way that analyzing the pitch of a sound emitted by a hollow instrument can tell you about the size and shape of both the instrument and the object that struck it.)

The researchers confirmed that the merged black hole was consistent with what is known as a “Kerr black hole.” The mathematician Roy Kerr, working in the 1960s, solved Einstein’s space-time equations, positing a detailed mathematical solution of what the exact gravity, space, and time of a black hole should be. Physicists believe that all black holes must be described by Kerr's solution, but confirming this is famously challenging. By studying the vibrations of the final black hole in this exceptionally clear signal, Isi and the LIGO Collaboration have obtained the most direct evidence yet that black holes behave like Kerr predicted.

“Over the next decade, gravitational wave detectors like LIGO will continue to improve, giving us a sharper view of black holes and their mysteries,” Isi said, “I can't wait to see what we find out.”

Journal

Physical Review Letters

DOI

10.1103/kw5g-d732

Method of Research

Data/statistical analysis

Subject of Research

Not applicable

Article Title

GW250114: testing Hawking’s area law and the Kerr nature of black holes

Article Publication Date

10-Sep-2025

Ten years later, LIGO is a black-hole hunting machine

LIGO, Virgo, and KAGRA celebrate anniversary, announce verification of Stephen Hawking's Black Hole Area Theorem

California Institute of Technology

On September 14, 2015, a signal arrived on Earth, carrying information about a pair of remote black holes that had spiraled together and merged. The signal had traveled about 1.3 billion years to reach us at the speed of light—but it was not made of light. It was a different kind of signal: a quivering of space-time called gravitational waves first predicted by Albert Einstein 100 years prior. On that day 10 years ago, the twin detectors of the US National Science Foundation Laser Interferometer Gravitational-Wave Observatory (NSF LIGO) made the first-ever direct detection of gravitational waves, whispers in the cosmos that had gone unheard until that moment.

The historic discovery meant that researchers could now sense the universe through three different means. While light waves, such as X-rays, optical, radio, and other wavelengths of light as well as high-energy particles called cosmic rays and neutrinos had been captured before, this was the first time anyone had witnessed a cosmic event through its gravitational warping of space-time. For this achievement, first dreamed up more than 40 years prior, three of the team's founders won the 2017 Nobel Prize in Physics: MIT's Rainer Weiss, professor of physics, emeritus (who recently passed away at age 92); Caltech's Barry Barish, the Ronald and Maxine Linde Professor of Physics, Emeritus; and Caltech's Kip Thorne, the Richard P. Feynman Professor of Theoretical Physics, Emeritus.

Today, LIGO, which consists of detectors in both Hanford, Washington and Livingston, Louisiana, routinely observes roughly one black hole merger every three days. LIGO now operates in coordination with two international partners, the Virgo gravitational-wave detector in Italy and KAGRA in Japan. Together, the gravitational-wave-hunting network, known as the LVK (LIGO, Virgo, KAGRA), has captured a total of about 300 black hole mergers, some of which are confirmed while others await further analysis. During the network's current science run, the fourth since the first run in 2015, the LVK has discovered about 220 candidate black hole mergers, more than double the number caught in the first three runs.

The dramatic rise in the number of LVK discoveries over the past decade is owed to several improvements to their detectors—some of which involve cutting-edge quantum precision engineering. The LVK detectors remain by far the most precise rulers for making measurements ever created by humans. The space-time distortions induced by gravitational waves are incredibly miniscule. For instance, LIGO detects changes in space-time smaller than 1/10,000 the width of a proton. That's 700 trillion times smaller than the width of a human hair.

"Rai Weiss proposed the concept of LIGO in 1972, and I thought 'this doesn't have much chance at all of working,'" recalls Thorne, an expert on the theory of black holes. "It took me three years of thinking about it on and off and discussing ideas with Rai and Vladimir Braginsky [a Russian physicist], to be convinced this had a significant possibility of success. The technical difficulty of reducing the unwanted noise that interferes with the desired signal was enormous. We had to invent a whole new technology. NSF was just superb at shepherding this project through technical reviews and hurdles."

MIT's Nergis Mavalvala, the Curtis and Kathleen Marble Professor of Astrophysics and dean of the School of Science, says that the challenges the team overcame to make the first discovery are still very much at play. "From the exquisite precision of the LIGO detectors, to the astrophysical theories of gravitational-wave sources, to the complex data analyses, all these hurdles had to be overcome, and we continue to improve in all of these areas. As the detectors get better, we hunger for farther, fainter sources. LIGO continues to be a technological marvel."

The Clearest Signal Yet

LIGO's improved sensitivity is exemplified in a recent discovery of a black hole merger referred to as GW250114 (the numbers denote the date the gravitational-wave signal arrived at Earth: January 14, 2025). The event was not that different from LIGO's first-ever detection (called GW150914)—both involve colliding black holes about 1.3 billion light-years away with masses between 30 to 40 times that of our Sun. But thanks to 10 years of technological advances reducing instrumental noise, the GW250114 signal is dramatically clearer.

By analyzing the frequencies of gravitational waves emitted by the merger, the LVK team was able to provide the best observational evidence captured to date for what is known as the black hole area theorem, an idea put forth by Stephen Hawking in 1971 that says the total surface areas of black holes cannot decrease. When black holes merge, their masses combine, increasing the surface area. But they also lose energy in the form of gravitational waves. Additionally, the merger can cause the combined black hole to increase its spin, which leads to it having a smaller area. The black hole area theorem states that despite these competing factors, the total surface area must grow in size.

In essence, the LIGO detection allowed the team to "hear" two black holes growing as they merged into one, verifying Hawking's theorem. (Virgo and KAGRA were offline during this particular observation.) The initial black holes had a total surface area of 240,000 square kilometers (roughly the size of Oregon), while the final area was about 400,000 square kilometers (roughly the size of California)—a clear increase. This is the second test of the black hole area theorem; an initial test was performed in 2021 using data from the first GW150914 signal, but because that data was not as clean, the results had a confidence level of 95 percent as compared to 99.999 percent for the new data.

Thorne recalls Hawking phoning him to ask whether LIGO might be able to test his theorem immediately after he learned of the 2015 gravitational-wave detection. Hawking died in 2018 and sadly did not live to see his theory observationally verified. "If Hawking were alive, he would have reveled in seeing the area of the merged black holes increase," Thorne says.

In the new study, the researchers were able to precisely measure the details of the ringdown phase, which allowed them to calculate the mass and spin of the black hole, and subsequently determine its surface area. More precisely, they were able, for the first time, to confidently pick out two distinct gravitational-wave modes in the ringdown phase. The modes are like characteristic sounds a bell would make when struck; they have somewhat similar frequencies but die out at different rates, which makes them hard to identify. The improved data for GW250114 meant that the team could extract the modes, demonstrating that the black hole's ringdown occurred exactly as predicted by math models based on the Teukolsky formalism—devised in 1972 by Saul Teukolsky, now a professor at Caltech and Cornell.

Another study from the LVK, submitted to Physical Review Letters today, places limits on a predicted third, higher-pitch tone in the GW250114 signal, and performs some of the most stringent tests yet of general relativity's accuracy in describing merging black holes.

"A decade of improvements allowed us to make this exquisite measurement," Chatziioannou says. "It took both of our detectors, in Washington and Louisiana, to do this. I don't know what will happen in 10 more years, but in the first 10 years, we have made tremendous improvements to LIGO's sensitivity. This not only means we are accelerating the rate at which we discover new black holes, but we are also capturing detailed data that expand the scope of what we know about the fundamental properties of black holes."

Jenne Driggers, detection lead senior scientist at LIGO Hanford, adds, "It takes a global village to achieve our scientific goals. From our exquisite instruments, to calibrating the data very precisely, vetting and providing assurances about the fidelity of the data quality, searching the data for astrophysical signals, and packaging all that into something that telescopes can read and act upon quickly, there are a lot of specialized tasks that come together to make LIGO the great success that it is."

Pushing the Limits

LIGO and Virgo have also unveiled neutron stars over the past decade. Like black holes, neutron stars form from the explosive deaths of massive stars, but they weigh less and glow with light. Of note, in August of 2017, LIGO and Virgo witnessed an epic collision between a pair of neutron stars—a kilonova—that sent gold and other heavy elements flying into space and drew the gaze of dozens of telescopes around the world, which captured light ranging from high-energy gamma rays to low-energy radio waves. The "multi-messenger" astronomy event marked the first time that both light and gravitational waves had been captured in a single cosmic event. Today, the LVK continues to alert the astronomical community to potential neutron star collisions, who then use telescopes to search the skies for signs of kilonovae.

"The LVK has made big strides in recent years to make sure we're getting high quality data and alerts out to the public in under a minute, so that astronomers can look for multi-messenger signatures from our gravitational-wave candidates," Driggers says.

Other LVK scientific discoveries include the first detection of collisions between one neutron star and one black hole; asymmetrical mergers, in which one black hole is significantly more massive than its partner black hole; the discovery of the lightest black holes known, challenging the idea that there is a "mass gap" between neutron stars and black holes; and the most massive black hole merger seen yet with a merged mass of 225 solar masses. For reference, the previous record-holder for the most massive merger had a combined mass of 140 solar masses.

Even in the decades before LIGO began taking data, scientists were building foundations that made the field of gravitational-wave science possible. Breakthroughs in computer simulations of black hole mergers, for example, allow the team to extract and analyze the feeble gravitational-wave signals generated across the universe.

LIGO's technological achievements, beginning as far back as the 1980s, include several far-reaching innovations, such as a new way to stabilize lasers using the so-called Pound–Drever–Hall technique. Invented in 1983 and named for contributing physicists Robert Vivian Pound, the late Ronald Drever of Caltech (a founder of LIGO), and John Lewis Hall, this technique is widely used today in other fields, such as the development of atomic clocks and quantum computers. Other innovations include cutting-edge mirror coatings that almost perfectly reflect laser light; "quantum squeezing" tools that enable LIGO to surpass sensitivity limits imposed by quantum physics; and new AI methods that could further hush certain types of unwanted noise.

"What we are ultimately doing inside LIGO is protecting quantum information and making sure it doesn't get destroyed by external factors," Mavalvala says. "The techniques we are developing are pillars of quantum engineering and have applications across a broad range of devices, such as quantum computers and quantum sensors."

In the coming years, the scientists and engineers of LVK hope to further fine tune their machines, expanding their reach deeper and deeper into space. They also plan to use the knowledge they have gained to build another gravitational-wave detector, LIGO India. Having a third LIGO observatory would greatly improve the precision with which the LVK network can localize gravitational-wave sources.

Looking farther into the future, the team is working on a concept for an even larger detector, called Cosmic Explorer, which would have arms 40 kilometers long (the twin LIGO observatories have 4-kilometer arms). A European project, called Einstein Telescope, also has plans to build one or two huge underground interferometers with arms of more than 10-kilometers long. Observatories on this scale would allow scientists to hear the earliest black hole mergers in the universe.

"Just ten short years ago, LIGO opened our eyes for the first time to gravitational waves and changed the way humanity sees the cosmos," says Aamir Ali, a program director in the NSF Division of Physics, which has supported LIGO since its inception. "There's a whole universe to explore through this completely new lens and these latest discoveries show LIGO is just getting started."

The LIGO-Virgo-KAGRA Collaboration

LIGO is funded by the US National Science Foundation and operated by Caltech and MIT, which togetherconceived and built the project. Financial support for the Advanced LIGO project was led by NSF with Germany (Max Planck Society), the United Kingdom (Science and Technology Facilities Council), and Australia (Australian Research Council) making significant commitments and contributions to the project. More than 1,600 scientists from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration. Additional partners are listed at my.ligo.org/census.php.

The Virgo Collaboration is currently composed of approximately 1,000 members from 175 institutions in 20 different (mainly European) countries. The European Gravitational Observatory (EGO) hosts the Virgo detector near Pisa in Italy, and is funded by Centre National de la Recherche Scientifique (CNRS) in France, the National Institute of Nuclear Physics (INFN) in Italy, the National Institute of Subatomic Physics (Nikhef) in the Netherlands, The Research Foundation – Flanders (FWO), and the Belgian Fund for Scientific Research (F.R.S.–FNRS). A list of the Virgo Collaboration groups can be found at: https://www.virgo-gw.eu/about/scientific-collaboration/. More information is available on the Virgo website at https://www.virgo-gw.eu.

Written by Whitney Clavin/Caltech

Journal

Physical Review Letters

Researchers uncover potential biosignatures on Mars

Texas A&M University

image:
Rocks in the Bright Angel Formation. NASA’s Mars Perseverance rover acquired this image using its Right Mastcam-Z camera. Mastcam-Z is a pair of cameras located high on the rover’s mast. This image was acquired on May 29, 2024 (Sol 1164) at the local mean solar time of 12:40:40.
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Credit: NASA/JPL-Caltech/ASU

A new study co-authored by Texas A&M University geologist Dr. Michael Tice has revealed potential chemical signatures of ancient Martian microbial life in rocks examined by NASA’s Perseverance rover.

The findings, published by a large international team of scientists, focus on a region of Jezero Crater known as the Bright Angel formation — a name chosen from locations in Grand Canyon National Park because of the light-colored Martian rocks. This area in Mars’ Neretva Vallis channel contains fine-grained mudstones rich in oxidized iron (rust), phosphorus, sulfur and — most notably — organic carbon. Although organic carbon, potentially from non-living sources like meteorites, has been found on Mars before, this combination of materials could have been a rich source of energy for early microorganisms.

“When the rover entered Bright Angel and started measuring the compositions of the local rocks, the team was immediately struck by how different they were from what we had seen before,” said Tice, a geobiologist and astrobiologist in the Department of Geology and Geophysics. “They showed evidence of chemical cycling that organisms on Earth can take advantage of to produce energy. And when we looked even closer, we saw things that are easy to explain with early Martian life but very difficult to explain with only geological processes.”

Tice went on to explain that “living things do chemistry that generally occurs in nature anyway given enough time and the right circumstances. To the best of our current knowledge, some of the chemistry that shaped these rocks required either high temperatures or life, and we do not see evidence of high temperatures here. However, these findings require experiments and ultimately laboratory study of the sample here on Earth in order to completely rule out explanations without life.”

The team published its findings in Nature.

A window into Mars’ watery past

The Bright Angel formation is composed of sedimentary rocks deposited by water, including mudstones (fine-grained sedimentary rocks made of silt and clay) and layered beds that suggest a dynamic environment of flowing rivers and standing water. Using Perseverance’s suite of instruments, including the SHERLOC and PIXL spectrometers, scientists detected organic molecules and small arrangements of minerals that appear to have formed through “redox reactions,” chemical processes involving the transfer of electrons. On Earth, those processes are often driven by biological activity.

Among the most striking features are tiny nodules and “reaction fronts”— nicknamed “poppy seeds” and “leopard spots” by the rover team — enriched in ferrous iron phosphate (likely vivianite) and iron sulfide (likely greigite). These minerals commonly form in low-temperature, water-rich environments and are often associated with microbial metabolisms.

“It’s not just the minerals, it’s how they are arranged in these structures that suggests that they formed through the redox cycling of iron and sulfur,” Tice said. “On Earth, things like these sometimes form in sediments where microbes are eating organic matter and ‘breathing’ rust and sulfate. Their presence on Mars raises the question: could similar processes have occurred there?”

Organic matter and redox chemistry

The SHERLOC instrument detected a Raman spectral feature known as the G-band, a signature of organic carbon, in several Bright Angel rocks. The strongest signals came from a site called “Apollo Temple,” where both vivianite and greigite were most abundant.

“This co-location of organic matter and redox-sensitive minerals is very compelling,” said Tice. “It suggests that organic molecules may have played a role in driving the chemical reactions that formed these minerals.”

Tice notes it’s important to understand that “organic” does not necessarily mean formed by living things.

“It just means having a lot of carbon-carbon bonds,” he explained. “There are other processes that can make those besides life. The kind of organic matter detected here could have been produced by abiotic processes or it could have been produced by living things. If produced by living things, it would have to have been degraded by chemical reactions, radiation or heat to produce the G-band that we observe now.”

The study outlines two possible scenarios: one in which these reactions occurred abiotically (driven by geochemical processes) and another in which microbial life may have affected the reactions, as it does on Earth. Strikingly, although some features of the nodules and reaction fronts could be produced by abiotic reactions between organic matter and iron, the known geochemical processes that could have produced the features associated with sulfur usually only work at relatively high temperatures.

“All the ways we have of examining these rocks on the rover suggest that they were never heated in a way that could produce the leopard spots and poppy seeds,” said Tice. “If that’s the case, we have to seriously consider the possibility that they were made by creatures like bacteria living in the mud in a Martian lake more than three billion years ago.”

While the team emphasizes that the evidence is not definitive proof of past life, the findings meet NASA’s criteria for “potential biosignatures” — features that warrant further investigation to determine whether they are biological or abiotic in origin.

A sample worth returning

Perseverance collected a core sample from the Bright Angel formation, named “Sapphire Canyon,” which is now stored in a sealed tube carried by the rover. This sample is among those prioritized for return to Earth in a potential future mission.

“Bringing this sample back to Earth would allow us to analyze it with instruments far more sensitive than anything we can send to Mars,” said Tice. “We’ll be able to look at the isotopic composition of the organic matter, the fine-scale mineralogy, and even search for microfossils if they exist. We’d also be able to perform more tests to determine the highest temperatures experienced by these rocks, and whether high temperature geochemical processes might still be the best way to explain the potential biosignatures.”

Tice, who has long studied ancient microbial ecosystems on Earth, said the parallels between Martian and terrestrial processes are striking — with one important difference.

“What’s fascinating is how life may have been making use of some of the same processes on Earth and Mars at around the same time,” he said. “We see evidence of microorganisms reacting iron and sulfur with organic matter in the same way in rocks of the same age on Earth, but we’d never be able to see exactly the same features that we see on Mars in the old rocks here. Processing by plate tectonics has heated all our rocks too much to preserve them this way. It’s a special and spectacular thing to be able to see them like this on another planet.”

Perseverance rover reached the Bright Angel site on Mars by navigating through a dune field, bypassing large boulders. The rover is now investigating this area’s unique geological features to understand Mars’ past environmental conditions and support future human exploration.

Credit

NASA/JPL-Caltech

Texas A&M University astrogeologist Dr. Michael Tice

Credit

Texas A&M University

Journal

Nature

DOI

10.1038/s41586-025-09413-0

Article Title

Redox-driven mineral and organic associations in Jezero Crater, Mars

Article Publication Date

10-Sep-2025

Potential biosignatures' found in ancient Mars lake

A new study suggests a habitable past and signs of ancient microbial processes on Mars - and Imperial scientists provided crucial context.

Imperial College London

A new study suggests a habitable past and signs of ancient microbial processes on Mars - and Imperial scientists provided crucial context.

Led by NASA and featuring key analysis from Imperial College London, the work has uncovered a range of minerals and organic matter in Martian rocks that point to an ancient history of habitable conditions and potential biological processes on the Red Planet.

An international team, including researchers from the Department of Earth Science and Engineering (ESE) at Imperial, propose that these geological features within the so-called Bright Angel formation in Mars's Jezero Crater are closely connected to organic carbon, and could be a compelling potential biosignature of past life.

Professor Sanjeev Gupta, Professor of Earth Science in ESE, and Academic Co-director of Imperial Global India, said: "This is a very exciting discovery of a potential biosignature but it does not mean we have discovered life on Mars. We now need to analyse this rock sample on Earth to truly confirm if biological processes were involved or not."

Promising signs

A core component of NASA’s Mars 2020 mission, the Perseverance Rover has been exploring the 45-kilometre-wide Jezero Crater since 2021, a site chosen because it once held a huge lake and a river delta – environments that are considered prime targets in the search for signs of past life. Its key goal is to collect and store the first set of selected rock and soil samples that will be brought back to Earth for detailed analysis.

The new study, published in Nature, focuses on a distinctly light-toned outcrop in the crater, dubbed ‘Bright Angel’, located within an ancient river valley which provided water to the Jezero lake.

While driving through the valley, called Neretva Vallis, Perseverance came across a thick succession of fine-grained mudstones and muddy conglomerates. Here, it conducted a detailed analysis of these rocks, using instruments such as the Planetary Instrument for X-ray Lithochemistry (PIXL) and Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals (SHERLOC).

An unexpected lake

By mapping the types and distributions of different sedimentary rocks at Bright Angel, ESE researchers (including Professor Gupta and Dr Robert Barnes, a Research Associate in ESE, who were both funded by the UK Space Agency), were able to reconstruct the environment in which these mudstones were deposited.

Their analysis revealed a range of sedimentary structures and textures indicative of lake margin and lake bed environments, including a composition rich in minerals like silica and clays – the opposite to a river scenario, where fast-moving water would carry these tiny particles away.

This pointed to a surprising conclusion: they had found lake deposits in the bottom of a river valley.

Co-author Alex Jones, a PhD researcher in ESE and collaborating scientist with the NASA Perseverance team, who has conducted a detailed analysis of the ancient lake environment, said: "This is unusual but very intriguing, as we wouldn’t expect to find such deposits in Neretva Vallis. What our sedimentological and stratigraphic work has done is indicate a past, low-energy lake environment – and that is precisely the kind of habitable environment we have been looking for on the mission."

The finding may suggest a period in the history of Jezero Crater where the valley itself was flooded, giving rise to this potentially habitable lake.

Alex, who is an Imperial President’s Scholar and did his undergraduate degree in Earth and Planetary Science at ESE, added: "I'm thrilled to be involved in such a discovery and contributing to Perseverance operations during my PhD. It’s also pretty cool to apply my terrestrial geologic field experience I gained as a student to investigate such an exciting unit at Jezero!"

Compelling context

With the lake habitat scenario pinned down, the Perseverance science team turned their attention to the mudstones themselves. It was inside these rocks that they discovered a group of tiny nodules and reaction fronts, with chemical analysis revealing that these millimetre-scale structures are highly enriched in iron-phosphate and iron-sulfide minerals (likely vivianite and greigite).

These appear to have formed through redox reactions involving organic carbon, a process that could have been driven by either abiotic or – interestingly – biological chemistry. Importantly, this sets the stage for everything that happened next: the formation of this specific type of oxidised, iron- and phosphorus-rich sediment was the essential prerequisite for creating the ingredients for subsequent reactions.

Since these ingredients mirror by-products of microbial metabolism seen on Earth, it can be considered a compelling potential biosignature, raising the possibility that there was once microbial life on Mars.

A question for Earth labs

Ultimately, the only way for the true origin of these structures to be determined is by returning the samples to Earth, a possibility that rests on when future missions will manage to successfully collect the samples from Mars’ surface.

Fortunately, Perseverance has already drilled and cached a core sample from the Bright Angel outcrop, named ‘Sapphire Canyon’, which, along with others collected by the rover, is awaiting the Mars Sample Return mission – a joint NASA-ESA endeavour aiming to bring them to Earth in the 2030s.

Once in terrestrial laboratories, samples like Sapphire Canyon will be analysed with instruments far more sensitive than those on the rover by scientists from around the world. Only then will we determine the precise origin of these features and whether they are the result of unique abiotic chemistry, or constitute evidence of past microbial life on Mars.

"This discovery is a huge step forward – the samples we helped characterise are among the most convincing we have," said Professor Gupta.

"The work was an impressive international effort and highlights the power of collaboration and advanced robotics in planetary exploration."

Matthew Cook, Head of Space Exploration at the UK Space Agency, said: "This exciting discovery represents a significant step forward in our understanding of Mars and the potential for ancient life beyond Earth. The chemical signatures identified in these Martian rocks are the first of their kind to potentially reflect biological processes that we see on Earth and provide more compelling evidence that Mars may have once harboured the conditions necessary for microbial life.

"Professor Sanjeev Gupta and his team at Imperial College London, supported through UK Space Agency funding, have made an invaluable contribution to this ground-breaking research, demonstrating the world-leading UK exploration science by leading the establishment of the geological context for the research.

"While we must remain scientifically cautious about definitive claims of ancient life, these findings represent the most promising evidence yet discovered. The upcoming Rosalind Franklin Mars rover mission, built here in the UK, will be crucial in helping us answer whether samples similar to those observed in this study represent genuine biological processes, bringing us closer to answering: are we alone in the Universe?"

Journal

Nature

DOI

10.1038/s41586-025-09413-0

An exploding black hole could reveal the foundations of the universe

UMass Amherst physicists think we could see such an explosion in the next 10 years—and it would ‘revolutionize physics and rewrite the history of the universe’

University of Massachusetts Amherst

Primordial Black Holes — image:
This artist's concept takes a fanciful approach to imagining small primordial black holes. In reality, such tiny black holes would have a difficult time forming the accretion disks that make them visible here.
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Credit: NASA's Goddard Space Flight Center

AMHERST, Mass. — Physicists have long believed that black holes explode at the end of their lives, and that such explosions happen—at most—only once every 100,000 years. But new research published in Physical Review Letters by physicists at the University of Massachusetts Amherst has found a more than 90% probability that one of these black-hole explosions might be seen within the decade, and that, if we are prepared, our current fleet of space and earthbound telescopes could witness the event.

Such an explosion would be strong evidence of a theorized but never observed kind of black hole, called a “primordial black hole,” that could have formed less than a second after the Big Bang occurred, 13.8 billion years ago. Furthermore, the explosion would give us a definitive catalog of all the subatomic particles in existence, including the ones we have observed, such as electrons, quarks and Higgs bosons, the ones that we have only hypothesized, like dark matter particles, as well as everything else that is, so far, entirely unknown to science. This catalog would finally answer one of humankind’s oldest questions: from where did everything in existence come?

We know that black holes exist, and we have a good understanding of their life cycle: an old, large star runs out of fuel, implodes in a massively powerful supernova and leaves behind an area of spacetime with such intense gravity that nothing, not even light, can escape. These black holes are incredibly heavy and are essentially stable.

But, as physicist Stephen Hawking pointed out in 1970, another kind of black hole—a primordial black hole (PBH), could be created not by the collapse of a star but from the universe’s primordial conditions shortly after the Big Bang. PBHs, like the standard black holes, are so massively dense that almost nothing can escape them—which is what makes them “black.” However, despite their density, PBHs could be much lighter than the black holes we have so far observed. Furthermore, Hawking also showed that black holes have a temperature and could, in theory, slowly emit particles via what is now known as “Hawking radiation” if they got hot enough.

“The lighter a black hole is, the hotter it should be and the more particles it will emit. As PBHs evaporate, they become ever lighter, and so hotter, emitting even more radiation in a runaway process until explosion. It’s that Hawking radiation that our telescopes can detect,” says Andrea Thamm, co-author and assistant professor of physics at UMass Amherst.

Yet, while we should be able to, no one has ever directly observed a PBH.

“We know how to observe this Hawking radiation,” says Joaquim Iguaz Juan, a postdoctoral researcher in physics at UMass Amherst. “We can see it with our current crop of telescopes, and because the only black holes that can explode today or in the near future are these PBHs, we know that if we see Hawking radiation, we are seeing an exploding PBH.”

Though physicists since Hawking’s time have thought that the chances of seeing an exploding PBH are infinitesimally slight, Iguaz Juan notes that “our job as physicists is to question the received assumptions, to ask better questions and come up with more precise hypotheses.”

The team’s new hypothesis? Get ready now to see the explosion. “We believe that there is up to a 90% chance of witnessing an exploding PBH in the next 10 years,” says Aidan Symons, one of the paper’s co-authors and a graduate student in physics at UMass Amherst.

In its work, the team explores a “dark-QED toy model.” This is essentially a copy of the usual electric force as we know it, but which includes a very heavy, hypothesized version of the electron, which the team calls a “dark electron.”

The team then reconsidered long-held assumptions about the electrical charge of black holes. Standard black holes have no charge, and it was assumed that PBHs are likewise electrically neutral.

“We make a different assumption,” says Michael Baker, co-author and an assistant professor of physics at UMass Amherst. “We show that if a primordial black hole is formed with a small dark electric charge, then the toy model predicts that it should be temporarily stabilized before finally exploding.” Taking all known experimental data into account, they find that we could then potentially observe a PBH explosion not once every 100,000 years as previously thought, but once every 10 years.

“We’re not claiming that it’s absolutely going to happen this decade,” says Baker, “but there could be a 90% chance that it does. Since we already have the technology to observe these explosions, we should be ready.”

Iguaz Juan adds, “this would be the first-ever direct observation of both Hawking radiation and a PBH. We would also get a definitive record of every particle that makes up everything in the universe. It would completely revolutionize physics and help us rewrite the history of the universe.”

About the University of Massachusetts Amherst

The flagship of the commonwealth, the University of Massachusetts Amherst is a nationally ranked public land-grant research university that seeks to expand educational access, fuel innovation and creativity and share and use its knowledge for the common good. Founded in 1863, UMass Amherst sits on nearly 1,450-acres in scenic Western Massachusetts and boasts state-of-the-art facilities for teaching, research, scholarship and creative activity. The institution advances a diverse, equitable, and inclusive community where everyone feels connected and valued—and thrives, and offers a full range of undergraduate, graduate and professional degrees across 10 schools and colleges and 100 undergraduate majors.

Primordial black holes [VIDEO]

This artist's concept takes a fanciful approach to imagining small primordial black holes. In reality, such tiny black holes would have a difficult time forming the accretion disks that make them visible here.

Credit

NASA's Goddard Space Flight Center

Journal

Physical Review Letters

DOI

10.1103/nwgd-g3zl

Article Title

Could We Observe an Exploding Black Hole in the Near Future?

Article Publication Date

10-Sep-2025

Hungry star is eating its cosmic twin at rate never seen before

Greedy white dwarf star not too far from Earth is devouring its closest celestial companion

University of Southampton

Greedy star snacking on its cosmic twin — image:
Double star V Sagittae - 10,000 light years from earth - is burning bright because greedy white dwarf is gorging on its larger twin
view more
Credit: University of Southampton

A greedy white dwarf star not far from Earth is devouring its closest celestial companion at a rate never seen before, space scientists have discovered.

Their study found the double star, named V Sagittae, is burning unusually bright as the super-dense white dwarf is gorging on its larger twin in a feeding frenzy.

Experts think the stars are locked in an extraterrestrial tango as they orbit each other every 12.3 hours, gradually pulling each other closer.

They say it could cause a massive explosion so bright it would be seen by the naked eye from Earth, some 10,000 lightyears away.

The findings were made by an international team of astronomers involving Professor Phil Charles from University of Southampton, led by Dr Pasi Hakala from the University of Turku in Finland with Dr Pablo Rodríguez Gil from the Spanish Instituto de Astrofisica de Canarias and University of La Laguna.

Southampton’s Professor Charles said their results crack a mystery about the star pair which has perplexed astronomers for a century.

He added: "V Sagittae is no ordinary star system – it's the brightest of its kind and has baffled experts since it was first discovered in 1902.

“Our study shows that this extreme brightness is down to the white dwarf sucking the life out of its companion star, using the accreted matter to turn it into a blazing inferno.

“It’s a process so intense that it's going thermonuclear on the white dwarf’s surface, shining like a beacon in the night sky.”

The new study was published in the Monthly Notices of the Royal Astronomical Society.

Researchers captured the cosmic carnage using the powerful European Southern Observatory’s Very Large Telescope in Chile – and made another discovery.

They found a ring of gas, like a giant halo, is encircling both stars, a consequence of the huge amounts of energy being generated by the hungry white dwarf.

This unexpected ring, formed from the debris of the messy feast, gives us a clue that could change what we know about how stars live and die, said lead author Dr Pasi Hakala from the University of Turku.

He added: “The white dwarf cannot consume all the mass being transferred from its hot star twin, so it creates this bright cosmic ring.

“The speed at which this doomed stellar system is lurching wildly, likely due to the extreme brightness, is a frantic sign of its imminent, violent end.”

Dr Rodríguez-Gil from Spain’s Instituto de Astrofisica de Canarias added: “The matter accumulating on the white dwarf is likely to produce a nova outburst in the coming years, during which V Sagittae would become visible with the naked eye.

“But when the two stars finally smash into each other and explode, this would be a supernova explosion so bright it’ll be visible from Earth even in the daytime."

Read the study at doi.org/10.48550/arXiv.2507.22637.

ENDS
472 WORDS

Journal

Monthly Notices of the Royal Astronomical Society

DOI

10.48550/arXiv.2507.22637

Method of Research

Meta-analysis

Subject of Research

Not applicable

Article Title

V Sge: Supersoft Source or Exotic Hot Binary? I. An X-Shooter campaign in the high state

Article Publication Date

10-Sep-2025

Predicting the green glow of aurorae on the red planet

Europlanet

image:
An artist’s impression of how the aurora might appear in the sky above the Perseverance rover.
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Credit: Alex McDougall-Page, University of Strathclyde/AstrollCareers.

Planetary scientists believe they can now predict the green glow of an aurora in the night sky above Mars, and they have the images to prove it.

The first observations of a visible-light aurora from the surface of the Red Planet were made by NASA’s Perseverance Mars rover in 2024. Now, presenting at the Europlanet Science Congress–Division of Planetary Science (EPSC–DPS) joint meeting in Helsinki this week, Dr Elise Wright Knutsen of the University of Oslo will reveal a second snapshot of the aurora by Perseverance and, more importantly, the tools to predict when an aurora will occur on Mars.

"The fact that we captured the aurora again demonstrates that our method for predicting aurorae on Mars and capturing them works," said Knutsen, who was also the science lead for the first image of a martian aurora seen from the ground.

Aurorae are produced when a burst of energetic particles in the solar wind, belched out by a coronal mass ejection (CME) from the Sun, collide with molecules in the atmosphere, causing them to glow. Mars’s aurorae glow green as a result of the charged particles colliding with oxygen atoms high above the Red Planet, and could be bright enough that astronauts on Mars would be able to see them with the naked eye. Furthermore, because Mars does not have a magnetic field to direct the charged particles to the magnetic poles, which is where we generally see aurorae on Earth, the martian aurorae are seen all across the night-side of the planet at the same as a glow in the sky. This is called ‘diffuse’ aurora.

The same radiation that causes the aurora could also potentially be dangerous to astronauts without warning that they must take shelter, so having some idea of when a powerful solar storm will hit Mars is crucial if humans are going to one day survive on the surface.

Nonetheless, predicting aurorae on Mars is a complex business. Observations have to be planned and uploaded to the rover three days ahead once a CME bursts out in the direction of Mars. This means a lot of guesswork as to which solar storms will produce an aurora.

Knutsen’s team made eight attempts to view the aurora with Perseverance’s SuperCam and MastCam cameras between 2023 and 2024, and they found it to be a process of trial and error. The first three attempts saw nothing, but by retrospectively analysing conditions as measured by NASA’s MAVEN and the ESA’s Mars Express orbiters, Knutsen and her colleagues realised that the velocities of those CMEs had likely not been fast enough to create a solar wind disturbance at Mars.

"The faster the CME, the more likely it is to accelerate particles towards Mars that create aurorae, and the stronger the solar wind disturbance around Mars, the more likely it is that those particles make it into Mars’s nightside atmosphere," said Knutsen. "Later, we progressively targeted faster, more intense CMEs, and that’s when we found our first two detections."

The final three CMEs also didn’t produce aurorae, even though they met the criteria that Knutsen was looking for.

"The last three non-detections are more curious," she said. "Statistically there is also a degree of randomness to these things, so sometimes we’re just unlucky. This perhaps isn’t that surprising, since predicting the aurora on Earth down to minute precision isn’t an exact science either."

Aurorae on Mars have previously been observed from orbit in ultraviolet light by ESA’s Mars Express and NASA’s MAVEN missions. Now, with the addition of visible-light detections, there is a growing dataset of observations for improving the accuracy of the aurora predictions. With further observations to come, they will hopefully help solve some ongoing mysteries about how the auroral lights are triggered on Mars.

"There is still much we don’t understand about how aurora occur on Mars as, unlike Earth, there is no global magnetic field to guide energetic solar particles onto the nightside where the aurora can be seen," said Knutsen. "Comparing the timing of solar wind disturbances, the arrival of solar energetic particles and the intensity and timing of aurora will advance our knowledge in this area."

Four images from Perseverance’s Mastcam-Z. The left hand-side images show both detections of the aurora, on 18 March and 18 May 2024. On the right are non-detections with comparable sky illumination (from Mars’s moons) to show the contrast in colours between a night with aurora and a night with no aurora. The March event was about twice as intense as the May event. The sky was also much dustier in May, which led to fewer stars being visible. The sky is generally much brighter and warmer in color in March due to Phobos, Mars’s largest moon, being in the sky. The coloured boxes show (from top to bottom): the theoretical aurora color for these images, the average sky colour, and the bottom boxes show the sky colour with the aurora signal removed or added, for left and right column respectively. This is to show what the colour of the sky would have been, theoretically, with no aurora that night, or with aurora for the comparison images. If all conditions were identical, then the two bottom boxes should diagonally have the same color, which worked close to perfectly for the May event. Below the images is the spectra from the rover’s SuperCam that identifies the green glow as the 557.7nm atomic oxygen auroral emission, indicated by the vertical green line. The solid lines are the real measurements for the two detections, while the dashed lines show our aurora model, demonstrating that the calculations estimating the aurora’s brightness from the surface with the measured dust amount corresponds very well with the observed aurora intensity.

Credit

Elise Wright Knutsen et al.

Look out for the keyhole: How to find the safest spots to deflect a hazardous asteroid

Europlanet

image:
One of the keyhole probability maps of the asteroid Bennu, The crosshair corresponds to the location on the surface that minimises the asteroid impact hazard after deflection. The maps assume a 25-metre targeting uncertainty for a kinetic impactor mission. As a result, deflection sites that could result in the kinetic impactor missing as a result of this uncertainty are not considered and form a grey boundary around the targetable region of the asteroid.
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Credit: Rahil Makadia.

Selecting the right spot to smash a spacecraft into the surface of a hazardous asteroid to deflect it must be done with great care, according to new research presented at the EPSC-DPS2025 Joint Meeting this week in Helsinki. Slamming into its surface indiscriminately runs the risk of knocking the asteroid through a 'gravitational keyhole' that sends it back around to hit Earth at a later date.

"Even if we intentionally push an asteroid away from Earth with a space mission, we must make sure it doesn't drift into one of these keyholes afterwards. Otherwise, we'd be facing the same impact threat again down the line," said Rahil Makadia, a NASA Space Technology Graduate Research Opportunity Fellow at the University of Illinois at Urbana-Champaign, who is presenting the findings at the EPSC-DPS2025 meeting.

NASA's DART, the Double Asteroid Redirection Test mission, struck the small asteroid Dimorphos, which is in orbit around the larger asteroid Didymos, in September 2022. DART was a 'kinetic impactor' – effectively a projectile that slammed into the asteroid with enough energy to nudge it into a new orbit, thereby proving that it is possible to deflect an asteroid that could be on a collision course with Earth.

A European Space Agency mission called Hera will follow-up on the DART impact when it reaches Didymos and Dimorphos in December 2026.

Where DART struck on Dimorphos was of relatively little concern, since the Didymos system is too massive to be deflected onto a collision course with Earth. However, for another hazardous asteroid orbiting the Sun, even a small variation in its orbit could send it through a gravitational keyhole.

The keyhole effect revolves around a small region of space where a planet's gravity can modify a passing asteroid's orbit such that it returns on a collision course with that planet at a later date. In this way, a gravitational keyhole unlocks more dangerous orbits.

Should a kinetic impactor mission similar to DART nudge a hazardous asteroid so that it passes through a gravitational keyhole, then it only postpones the danger.

"If an asteroid passed through one of these keyholes, its motion through the Solar System would steer it onto a path that causes it to hit Earth in the future," said Makadia.

The trick, therefore, is to find the best spot on the surface of an asteroid to impact with a spacecraft so that the chances of pushing it through the keyhole are minimised.

Each point on the surface of an asteroid has a different probability of sending the asteroid through a gravitational keyhole after deflection by a kinetic impactor. Makadia's team has therefore developed a technique for computing probability maps of an asteroid's surface. Their method uses the results from DART as a guide, although each asteroid, with its own characteristics, will be subtly different.

The asteroid's shape, surface topology (hills, craters etc), rotation and mass all must be determined first. Ideally this would be done with a space mission to rendezvous with the asteroid, producing high-resolution images and data. However, this might not be possible for all threatening asteroids, particularly if the time between discovery and impact on Earth is short.

“Fortunately, this entire analysis, at least at a preliminary level, is possible using ground-based observations alone, although a rendezvous mission is preferred,” said Makadia.

By computing the subsequent trajectory of the asteroid following a kinetic impact, and seeing which trajectories would be the most dangerous, scientists can calculate where the safest location to strike on the asteroid's surface will be.

"With these probability maps, we can push asteroids away while preventing them from returning on an impact trajectory, protecting the Earth in the long run," said Makadia.

An artwork of NASA’s DART mission, which was a kinetic impactor designed to test whether it is possible to deflect an asteroid.

Credit

NASA/Johns Hopkins APL.

Study questions ocean origin of organics in Enceladus’s plumes

Europlanet

image:
An artist’s impression of plumes erupting onto the surface of Enceladus. Its fellow moon Titan is seen in the sky, and the distant Sun beyond.
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Credit: ESA/Science Office.

Organic molecules detected in the watery plumes that spew out from cracks in the surface of Enceladus could be formed through exposure to radiation on Saturn’s icy moon, rather than originating from deep within its sub-surface ocean. The findings, presented during the EPSC–DPS2025 Joint Meeting in Helsinki this week, have repercussions for assessing the habitability of Enceladus’s ocean.

‘While the identification of complex organic molecules in Enceladus’s environment remains an important clue in assessing the moon’s habitability, the results demonstrate that radiation-driven chemistry on the surface and in the plumes could also create these molecules,’ said Dr Grace Richards, of the Istituto Nazionale di Astrofisica e Planetologia Spaziale (INAF) in Rome, who is presenting the results at the meeting.

The plumes were discovered in 2005 by NASA’s Cassini spacecraft. They emanate from long fractures called ‘tiger stripes’ that are located in Enceladus’s south polar region. The water comes from a sub-surface ocean, and the energy to heat the ocean and produce the plumes is the result of gravitational tidal forces from massive Saturn flexing Enceladus’s interior.

Cassini flew through the plumes, ‘tasting’ some of the molecules within them and finding them to be rich in salts as well as containing a variety of organic compounds. As organic compounds, dissolved in a subsurface ocean of water, could build into prebiotic molecules that are the precursors to life, these findings were of great interest to astrobiologists.

However, results of experiments by Richards and her colleagues show that the exposure to radiation trapped in Saturn’s powerful magnetosphere could trigger the formation of these organic compounds on Enceladus’s icy surface instead. This calls into question their astrobiological relevance.

Richards, with funding from Europlanet, visited facilities at the HUN-REN Institute for Nuclear Research in Hungary, where she and colleagues simulated the composition of ice on the surface and in the walls of Enceladus’s tiger stripes. This ice contained water, carbon dioxide, methane and ammonia and was cooled to -200 degrees Celsius. Richards’s team then bombarded the ice with ions – atoms and molecules stripped of an electron – to replicate the radiation environment around Enceladus. The ions reacted with the icy components, creating a whole swathe of molecular species, including carbon monoxide, cyanate and ammonium. They also produced molecular precursors to amino acids, chains of which form proteins that drive metabolic reactions, repair cells and convey nutrients in lifeforms.

Some of these compounds have previously been detected on the surface of Enceladus, but others have also been identified in the plumes.

‘Molecules considered prebiotic could plausibly form in situ through radiation processing, rather than necessarily originating from the subsurface ocean,’ said Richards. ‘Although this doesn’t rule out the possibility that Enceladus’s ocean may be habitable, it does mean we need to be cautious in making that assumption just because of the composition of the plumes.’

Understanding how to differentiate between ocean-derived organics and molecules formed by radiation interacting with the surface and the tiger stripes will be highly challenging. More data from future missions will be required, such as a proposed Enceladus mission that is currently under consideration as part of the Voyage 2050 recommendations for the European Space Agency (ESA)’s science programme up until the middle of the century.

Enceladus, imaged by the Cassini spacecraft.

Credit

NASA/JPL/Space Science Institute.

Enceladus’s plumes seen spraying up from the tiger stripes.

Credit

NASA/JPL/Space Science Institute.

Wednesday, September 10, 2025

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Clear Signal Sheds Light on Black Holes - Infographic

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The video plays each detection twice. The first round is played at the original frequencies, in which the gravitational-wave frequencies have been converted directly into sound waves. In the second round, the pitch has been increased by 30 percent to make the chirp easier to hear.

Listen for the low “whoosh” rising out of the background static—that's the sound of space-time itself rippling. Notice how much quieter the background noise is behind GW250114 compared to GW150914, an indication of how dramatically LIGO’s sensitivity has improved over the past decade.

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Perseverance rover reached the Bright Angel site on Mars by navigating through a dune field, bypassing large boulders. The rover is now investigating this area’s unique geological features to understand Mars’ past environmental conditions and support future human exploration.

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Texas A&M University astrogeologist Dr. Michael Tice

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Promising signs

An unexpected lake

Compelling context

A question for Earth labs

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An artwork of NASA’s DART mission, which was a kinetic impactor designed to test whether it is possible to deflect an asteroid.

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Enceladus, imaged by the Cassini spacecraft.

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Enceladus’s plumes seen spraying up from the tiger stripes.

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