SPACE
New cosmological constraints on the nature of dark matter
IMAGE: DARK MATTER FLUCTUATIONS IN THE LENS SYSTEM MG J0414+0534. THE WHITISH BLUE COLOR REPRESENTS THE GRAVITATIONALLY LENSED IMAGES OBSERVED BY ALMA. THE CALCULATED DISTRIBUTION OF DARK MATTER IS SHOWN IN ORANGE; BRIGHTER REGIONS INDICATE HIGHER CONCENTRATIONS OF DARK MATTER AND DARK ORANGE REGIONS INDICATE LOWER CONCENTRATIONS. view more
CREDIT: ALMA(ESO/NAOJ/NRAO), K. T. INOUE ET AL.
New research has revealed the distribution of dark matter in never before seen detail, down to a scale of 30,000 light-years. The observed distribution fluctuations provide better constraints on the nature of dark matter.
Mysterious dark matter accounts for most of the matter in the Universe. Dark matter is invisible and makes itself know only through its gravitational effects. Dark matter has never been isolated in a laboratory, so researchers must rely on “natural experiments” to study it.
One type of natural experiment is a gravitational lens. Sometimes by random chance, two objects at different distances in the Universe will lie along the same line-of-sight when seen from Earth. When this happens, the spatial curvature caused by the matter around the foreground object acts like a lens, bending the path of light from the background object and making a lensed image. However, it is difficult to achieve the high resolution to detect clumps of dark matter which are less massive than galaxies in natural experiments, so the exact nature of dark matter has been poorly constrained.
A team of Japanese researchers led by Professor Kaiki Taro Inoue at Kindai University used ALMA (Atacama Large Millimeter/submillimeter Array) to study the gravitational lens system known as MG J0414+0534 in the direction of the constellation Taurus. In this system, the foreground object forms not one, but four images of the background object due to the gravitational force of a massive galaxy acting on the light. With the help of the bending effect and their new data analysis method, the team was able to detect fluctuations in the dark matter distribution along the line-of-sight in higher resolution than ever before, down to a scale of 30,000 light-years.
A conceptual diagram of the gravitational lens system MG J0414+0534. Dark matter associated with the lensing galaxy is shown in pale blue and white. Dark matter in intergalactic space is shown in orange. Solid lines show the actual paths of the radio waves which are bent by gravity. Dotted lines show the apparent observed positions of the lensed images.
CREDIT
NAOJ, K. T. Inoue
The new constraints provided by the observed distribution are consistent with models for slow moving, or “cold,” dark matter particles.
In the future the team plans to further constrain the nature of dark matter with additional observations.
JOURNAL
The Astrophysical Journal
METHOD OF RESEARCH
Observational study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
ALMA Measurement of 10 kpc-scale Lensing Power Spectra towards the Lensed Quasar MG J0414+0534
ARTICLE PUBLICATION DATE
7-Sep-2023
NASA’s Swift learns a new trick, spots a snacking black hole
IMAGE: IN THIS ARTIST'S CONCEPT, A SUPERMASSIVE BLACK HOLE PULLS A STREAM OF GAS OFF A STAR THAT PASSES TOO CLOSE. view more
CREDIT: NASA’S GODDARD SPACE FLIGHT CENTER/CHRIS SMITH (USRA/GESTAR)
Using NASA’s Neil Gehrels Swift Observatory, which launched in 2004, scientists have discovered a black hole in a distant galaxy repeatedly nibbling on a Sun-like star. The object heralds a new era of Swift science made possible by a novel method for analyzing data from the satellite’s X-ray Telescope (XRT).
“Swift’s hardware, software, and the skills of its international team have enabled it to adapt to new areas of astrophysics over its lifetime,” said Phil Evans, an astrophysicist at the University of Leicester in the United Kingdom and longtime Swift team member. “Neil Gehrels, the mission’s namesake, oversaw and encouraged many of those transitions. Now, with this new ability, it’s doing even more cool science.”
Evans led a study about the unlucky star and its hungry black hole, collectively called Swift J023017.0+283603 (or Swift J0230 for short), which was published on Sept. 7 in Nature Astronomy.
When a star strays too close to a monster black hole, gravitational forces create intense tides that break the star apart into a stream of gas. The leading edge swings around the black hole, and the trailing edge escapes the system. These destructive episodes are called tidal disruption events. Astronomers see them as flares of multiwavelength light created when the debris collides with a disk of material already orbiting the black hole.
Recently, astronomers have been investigating variations on this phenomena, which they call partial or repeating tidal disruptions.
During these events, every time an orbiting star passes close to a black hole, the star bulges outward and sheds material, but survives. The process repeats until the star loses too much gas and finally breaks apart. The characteristics of the individual star and black hole system determine what kind of emission scientists observe, creating a wide array of behaviors to categorize.
Previous examples include an outburst that occurred every 114 days, potentially caused by a giant star orbiting a black hole with 78 million times the Sun’s mass. Another recurred every nine hours around a black hole with 400,000 times the Sun’s mass, likely caused by an orbiting stellar cinder called a white dwarf.
On June 22, 2022, the XRT captured Swift J0230 for the first time. It lit up in a galaxy around 500 million light-years away in the northern constellation Triangulum. Swift’s XRT observed nine additional outbursts from the same location roughly every few weeks.
Evans and his team propose that Swift J0230 is a repeating tidal disruption of a Sun-like star orbiting a black hole with over 200,000 times the Sun’s mass. They estimate the star loses around three Earth masses of material on each pass. This system provides a bridge between other types of suspected repeating disruptions and allowed scientists to model how interactions between different star types and black hole sizes affect what we observe.
“We searched and searched for the event brightening in the data collected by Swift’s Ultraviolet/Optical Telescope,” said Alice Breeveld, a research fellow at the University College London’s Mullard Space Science Laboratory (MSSL) who has worked on the instrument since before the satellite launched. “But there wasn’t any sign of it. The galaxy’s variability was entirely in X-rays. That helped rule out some other potential causes.”
Swift J0230’s discovery was possible thanks to a new, automated search of XRT observations, developed by Evans, called the Swift X-ray Transient Detector.
After the instrument observes a portion of the sky, the data is transmitted to the ground, and the program compares it to previous XRT snapshots of the same spot. If that portion of the X-ray sky has changed, scientists get an alert. In the case of Swift J0230, Evans and his colleagues were able to rapidly coordinate additional observations of the region.
Swift was originally designed to study gamma-ray bursts, the most powerful explosions in the cosmos. Since the satellite launched, however, scientists have recognized its ability to study a whole host of celestial objects, like tidal disruptions and comets.
“Swift J0230 was discovered only about two months after Phil launched his program,” said S. Bradley Cenko, the mission’s principal investigator at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “It bodes well for the detector’s ability to identify other transient events and for Swift’s future exploring new spaces of science.”
Goddard manages the Swift mission in collaboration with Penn State, the Los Alamos National Laboratory in New Mexico, and Northrop Grumman Space Systems in Dulles, Virginia. Other partners include Leicester, MSSL, Brera Observatory in Italy, and the Italian Space Agency.
JOURNAL
Nature Astronomy
ARTICLE TITLE
Monthly quasi-periodic eruptions from repeated stellar disruption by a massive black hole
ARTICLE PUBLICATION DATE
7-Sep-2023
Ravenous black hole consumes three Earths’-worth of star every time it passes
Massive burst of X-rays detected by University of Leicester astronomers indicates material three times the mass of Earth burning up in a black hole
IMAGE: NOW YOU DON’T SEE IT, NOW YOU DO! X-RAY IMAGES OF THE SAME LOCATION ON THE SKY BEFORE (LEFT) AND AFTER (RIGHT) SWIFT J0230 ERUPTED. THESE IMAGES WERE TAKEN WITH THE X-RAY TELESCOPE ON-BOARD THE SWIFT SATELLITE. view more
CREDIT: PHIL EVANS (UNIVERSITY OF LEICESTER) / NASA SWIFT
A star like our own Sun in a nearby galaxy is gradually being eaten away by a small but ravenous black hole, losing the equivalent mass of three Earths every time it passes close.
The discovery by University of Leicester astronomers is reported today (7 September) in Nature Astronomy and provides a ‘missing link’ in our knowledge of black holes disrupting orbiting stars. It suggests a whole menagerie of stars in the process of being consumed that still lie undiscovered.
The team was supported by the UK Space Agency and the UK Science and technology Facilities Council (STFC).
The astronomers were alerted to the star by a bright X-ray flash that seemed to come from the centre of the nearby galaxy 2MASX J02301709+2836050, around 500 million light-years away from the Milky Way. Named Swift J0230, it was spotted the moment it happened for the first time using a new tool developed by the scientists for the Neil Gehrels Swift Observatory. They rapidly scheduled further Swift observations of it, finding that instead of decaying away as expected, it would shine brightly for 7-10 days and then abruptly switch off, repeating this process roughly every 25 days.
Similar behaviour has been observed in what are termed quasi-periodic eruptions and periodic nuclear transients, where a star has material ripped away by a black hole as its orbit takes it close by, but they differ in how often they erupt, and in whether it is in X-rays or optical light that the explosion is predominant. The regularity of Swift J0230’s emissions fell between the two, suggesting that it forms the ‘missing link’ between the two types of outburst.
Using the models proposed for these two classes of event as a guide, the scientists concluded that the Swift J0230 outburst represents a star of a similar size to our own sun in an elliptical orbit around a low-mass black hole at the centre of its galaxy. As the star’s orbit takes it close to the intense gravitational pull of the black hole, material equivalent to the mass of three Earths is wrenched from the atmosphere of the star and heated up as it falls into the black hole. The intense heat, around 2 million degrees Celsius, releases a huge amount of X-rays which were first picked up by the Swift satellite.
Lead author Dr Phil Evans of the University of Leicester School of Physics and Astronomy said: “This is the first time we've seen a star like our Sun being repeatedly shredded and consumed by a low mass black hole. So-called ‘repeated, partial tidal disruption’ events are themselves quite a new discovery and seem to fall into two types: those that outburst every few hours, and those that outburst every year or so. This new system falls right into the gap between these, and when you run the numbers, you find the types of objects involved fall nicely into place too.”
Dr Rob Eyles-Ferris, who works with Dr Evans on the Swift satellite, recently completed his PhD at Leicester, which included the study of stars being disrupted by black holes. He explains: “In most of the systems we’ve seen in the past the star is completely destroyed. Swift J0230 is an exciting addition to the class of partially-disrupted stars as it shows us that the two classes of these objects already found are really connected, with our new system giving us the missing link.”
Dr Kim Page from the University of Leicester, who worked on the data analysis for the study, said: “Given that we found Swift J0230 within a few months of enabling our new transient-hunting tool, we expect that there are a lot more objects like this out there, waiting to be uncovered.”
Dr Chris Nixon is a theoretical astrophysicist who recently moved from the University of Leicester to the University of Leeds. He led the theoretical interpretation of this event. His research is funded by the UK Science and Technology Facilities Council and the Leverhulme Trust.
They estimate that the black hole is around 10,000 to 100,000 times the mass of our sun, which is quite small for the supermassive black holes usually found at the centre of galaxies. The black hole at the centre of our own galaxy is thought to be 4 million solar masses, while most are in the region of 100 million solar masses.
It is the first discovery to be made using the new transient detector for the Swift satellite, developed by the University of Leicester team and running on their computers. When an extreme event takes place, causing an X-ray burst in a region of the sky where there were previously no X-rays, astronomers call it an astronomical X-ray transient. Despite the extreme events they herald, these events are not easy to find, or at least, not quickly – and so this new tool was developed to look for new types of transients in real time.
Dr Evans adds: “This type of object was essentially undetectable until we built this new facility, and soon after it found this completely new, never-before-seen event. Swift is nearly 20 years old and it's suddenly finding brand new events that we never knew existed. I think it shows that every single time you find a new way of looking at space, you learn something new and find there's something out there you didn't know about before.”
Dr Caroline Harper, Head of Space Science at the UK Space Agency, said: “This is yet another exciting discovery from the world-leading Swift mission - a low mass black hole taking ‘bites’ from a Sun-like star whenever it orbits close enough.
“The UK Space Agency has been working in partnership with NASA on this mission for many years; the UK led on the development of hardware for two of the key science instruments and we provided funding for the Swift Science Data Centre, which we continue to support. We look forward to even more insights from Swift about gamma ray bursts throughout the cosmos, and the massive events that cause them, in the future.”
An optical image of the galaxy in which the new event occurred, taken from archival PanSTARRS data. The X-ray object was located to somewhere inside the white circle, which is about the size a pinhead 100m away would appear. The position of a 2 year old supernova is also shown.
CREDIT
Daniele B. Malesani / PanSTARRS
JOURNAL
Nature Astronomy
ARTICLE TITLE
‘Recurring X-ray eruptions from a galaxy nucleus: a candidate repeating stellar disruption around a supermassive black hole’
ARTICLE PUBLICATION DATE
7-Sep-2023
Study hints at the existence of the closest black holes to Earth in the Hyades star cluster
Black holes are one of the most mysterious and fascinating phenomena in the Universe
Peer-Reviewed PublicationIMAGE: IMAGE OF THE HYADES STAR CLUSTER view more
CREDIT: JOSE MTANOUS
A paper published in the journal Monthly Notices of the Royal Astronomical Society hints at the existence of several black holes in the Hyades cluster — the closest open cluster to our solar system — which would make them the closest black holes to Earth ever detected. The study results from a collaboration between a group of scientists led by Stefano Torniamenti, from the University of Padua (Italy), with the significant participation of with Mark Gieles, ICREA professor at the Faculty of Physics, the Institute of Cosmos Sciences of the University of Barcelona (ICCUB) and the Institute of Space Studies of Catalonia (IEEC), and Friedrich Anders (ICCUB-IEEC).
Specifically, the finding took place during a research stay of the expert Stefano Torniamenti at the ICCUB, one of the research units that make up the IEEC.
Black holes in the Hyades star cluster?
Since their discovery, black holes have been one of the most mysterious and fascinating phenomena in the Universe and have become the object of study for researchers all over the world. This is particularly true for small black holes because they have been observed during the detection of gravitational waves. Since the detection of the first gravitational waves in 2015, experts have observed many events that correspond to mergers of low-mass black hole pairs.
For the published study, the team of astrophysicists used simulations that track the motion and evolution of all the stars in the Hyades — located at a distance from the Sun of about 45 parsecs or 150 light-years — to reproduce their current state.
Open clusters are loosely bound groups of hundreds of stars that share certain properties such as age and chemical characteristics. The simulation results were compared with the actual positions and velocities of the stars in the Hyades, which are now known precisely from observations made by the European Space Agency's (ESA) Gaia satellite.
"Our simulations can only simultaneously match the mass and size of the Hyades if some black holes are present at the centre of the cluster today (or until recently)", says Stefano Torniamenti, postdoctoral researcher at the University of Padua and first author of the paper.
The observed properties of the Hyades are best reproduced by simulations with two or three black holes at present, although simulations where all the black holes have been ejected (less than 150 million years ago, roughly the last quarter of the cluster's age) can still give a good match, because the evolution of the cluster could not erase the traces of its previous black hole population.
The new results indicate that the Hyades-born black holes are still inside the cluster, or very close to the cluster. This makes them the closest black holes to the Sun, much closer than the previous candidate (namely the black hole Gaia BH1, which is 480 parsecs from the Sun).
In recent years, the breakthrough of the Gaia space telescope has made it possible for the first time to study the position and velocity of open cluster stars in detail and to identify individual stars with confidence.
"This observation helps us understand how the presence of black holes affects the evolution of star clusters and how star clusters in turn contribute to gravitational wave sources", says Mark Gieles, a member of the UB Department of Quantum Physics and Astrophysics and host of the first author in Barcelona. "These results also give us insight into how these mysterious objects are distributed across the galaxy”.
The new study is the result of close collaboration between the University of Padova, ICUBB-IEEC, the University of Cambridge (United Kingdome), the European Southern Observatory (ESO) and the National Sun Yat-sen University (China).
JOURNAL
Monthly Notices of the Royal Astronomical Society
METHOD OF RESEARCH
Observational study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Stellar-mass black holes in the Hyades star cluster?”
Webb reveals new structures within iconic supernova
IMAGE: WEBB’S NIRCAM (NEAR-INFRARED CAMERA) CAPTURED THIS DETAILED IMAGE OF SN 1987A (SUPERNOVA 1987A), WHICH HAS BEEN ANNOTATED TO HIGHLIGHT KEY STRUCTURES. AT THE CENTER, MATERIAL EJECTED FROM THE SUPERNOVA FORMS A KEYHOLE SHAPE. JUST TO ITS LEFT AND RIGHT ARE FAINT CRESCENTS NEWLY DISCOVERED BY WEBB. BEYOND THEM AN EQUATORIAL RING, FORMED FROM MATERIAL EJECTED TENS OF THOUSANDS OF YEARS BEFORE THE SUPERNOVA EXPLOSION, CONTAINS BRIGHT HOT SPOTS. EXTERIOR TO THAT IS DIFFUSE EMISSION AND TWO FAINT OUTER RINGS. IN THIS IMAGE BLUE REPRESENTS LIGHT AT 1.5 MICRONS (F150W), CYAN 1.64 AND 2.0 MICRONS (F164N, F200W), YELLOW 3.23 MICRONS (F323N), ORANGE 4.05 MICRONS (F405N), AND RED 4.44 MICRONS (F444W). view more
CREDIT: CREDITS: NASA, ESA, CSA, M. MATSUURA (CARDIFF UNIVERSITY), R. ARENDT (NASA’S GODDARD SPACEFLIGHT CENTER & UNIVERSITY OF MARYLAND, BALTIMORE COUNTY), C. FRANSSON (STOCKHOLM UNIVERSITY), AND J. LARSSON (KTH ROYAL INSTITUTE OF TECHNOLOGY). IMAGE PROCESSING: A. PAGAN
NASA’s James Webb Space Telescope has begun the study of one of the most renowned supernovae, SN 1987A (Supernova 1987A). Located 168,000 light-years away in the Large Magellanic Cloud, SN 1987A has been a target of intense observations at wavelengths ranging from gamma rays to radio for nearly 40 years, since its discovery in February of 1987. New observations by Webb’s NIRCam (Near-Infrared Camera) provide a crucial clue to our understanding of how a supernova develops over time to shape its remnant.
This image reveals a central structure like a keyhole. This center is packed with clumpy gas and dust ejected by the supernova explosion. The dust is so dense that even near-infrared light that Webb detects can’t penetrate it, shaping the dark “hole” in the keyhole.
A bright, equatorial ring surrounds the inner keyhole, forming a band around the waist that connects two faint arms of hourglass-shaped outer rings. The equatorial ring, formed from material ejected tens of thousands of years before the supernova explosion, contains bright hot spots, which appeared as the supernova’s shock wave hit the ring. Now spots are found even exterior to the ring, with diffuse emission surrounding it. These are the locations of supernova shocks hitting more exterior material.
While these structures have been observed to varying degrees by NASA’s Hubble and Spitzer Space Telescopes and Chandra X-ray Observatory, the unparalleled sensitivity and spatial resolution of Webb revealed a new feature in this supernova remnant – small crescent-like structures. These crescents are thought to be a part of the outer layers of gas shot out from the supernova explosion. Their brightness may be an indication of limb brightening, an optical phenomenon that results from viewing the expanding material in three dimensions. In other words, our viewing angle makes it appear that there is more material in these two crescents than there actually may be.
Webb’s NIRCam (Near-Infrared Camera) captured this detailed image of SN 1987A (Supernova 1987A), which has been annotated to highlight key structures. At the center, material ejected from the supernova forms a keyhole shape. Just to its left and right are faint crescents newly discovered by Webb. Beyond them an equatorial ring, formed from material ejected tens of thousands of years before the supernova explosion, contains bright hot spots. Exterior to that is diffuse emission and two faint outer rings. In this image blue represents light at 1.5 microns (F150W), cyan 1.64 and 2.0 microns (F164N, F200W), yellow 3.23 microns (F323N), orange 4.05 microns (F405N), and red 4.44 microns (F444W).
CREDIT
Credits: NASA, ESA, CSA, M. Matsuura (Cardiff University), R. Arendt (NASA’s Goddard Spaceflight Center & University of Maryland, Baltimore County), C. Fransson (Stockholm University), and J. Larsson (KTH Royal Institute of Technology). Image Processing: A. Pagan
Webb’s NIRCam (Near-Infrared Camera) captured this detailed image of SN 1987A (Supernova 1987A). At the center, material ejected from the supernova forms a keyhole shape. Just to its left and right are faint crescents newly discovered by Webb. Beyond them an equatorial ring, formed from material ejected tens of thousands of years before the supernova explosion, contains bright hot spots. Exterior to that is diffuse emission and two faint outer rings. In this image blue represents light at 1.5 microns (F150W), cyan 1.64 and 2.0 microns (F164N, F200W), yellow 3.23 microns (F323N), orange 4.05 microns (F405N), and red 4.44 microns (F444W).
CREDIT
Credits: NASA, ESA, CSA, M. Matsuura (Cardiff University), R. Arendt (NASA’s Goddard Spaceflight Center & University of Maryland, Baltimore County), C. Fransson
The high resolution of these images is also noteworthy. Before Webb, the now-retired Spitzer telescope observed this supernova in infrared throughout its entire lifespan, yielding key data about how its emissions evolved over time. However, it was never able to observe the supernova with such clarity and detail.
Despite the decades of study since the supernova’s initial discovery, there are several mysteries that remain, particularly surrounding the neutron star that should have been formed in the aftermath of the supernova explosion. Like Spitzer, Webb will continue to observe the supernova over time. Its NIRSpec (Near-Infrared Spectrograph) and MIRI (Mid-Infrared Instrument) instruments will offer astronomers the ability to capture new, high-fidelity infrared data over time and gain new insights into the newly identified crescent structures. Further, Webb will continue to collaborate with Hubble, Chandra, and other observatories to provide new insights into the past and future of this legendary supernova.
The James Webb Space Telescope is the world's premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
Hot Jupiter blows its top
Stampede2 simulations help capture helium gas clouds escaping distant planet
Peer-Reviewed PublicationIMAGE: THE PLANET HAT-P-32B IS LOSING SO MUCH OF ITS ATMOSPHERIC HELIUM THAT THE TRAILING GAS TAILS ARE AMONG THE LARGEST STRUCTURES YET KNOWN ANY PLANET OUTSIDE OUR SOLAR SYSTEM. SIMULATION ‘SLICE’ THROUGH THE ORBITAL PLANE APPROXIMATING THE HAT-P-32 A + B SYSTEM. view more
CREDIT: ZHANG ET AL., SCI. ADV. 9, EADF8736 (2023).
A planet about 950 light years from Earth could be the Looney Tunes’ Yosemite Sam equivalent of planets, blowing its atmospheric ‘top’ in spectacular fashion.
The planet called HAT-P-32b is losing so much of its atmospheric helium that the trailing gas tails are among the largest structures yet known of an exoplanet, a planet outside our solar system, according to observations by astronomers.
Three-dimensional (3D) simulations on the Stampede2 supercomputer of the Texas Advanced Computing Center (TACC) helped model the flow of the planet’s atmosphere, based on data from the Hobby-Eberly Telescope of The University of Texas at Austin's McDonald Observatory. The scientists hope to widen their planet-observing net and survey 20 additional star systems to find more planets losing their atmosphere and learn about their evolution.
“We have monitored this planet and the host star with long time series spectroscopy, observations made of the star and planet over a couple of nights. And what we found is there's a gigantic helium gas tail that is associated with the planet. The tail is large — about 53 times the planet’s radius — formed by gas that’s escaping from the planet,” said Zhoujian Zhang, a postdoctoral fellow in the Department of Astronomy & Astrophysics, University of California Santa Cruz.
Zhang is the lead author in a study on the helium tail detected from HAT-P 32b that was published in Science Advances June 2023. The science team used data from the Habitable Planet Finder spectrograph, an instrument on the Hobby-Eberly telescope, which provides high spectral resolution of light in near infrared wavelengths.
The planet HAT-P-32b was discovered in 2011 using spectroscopic data from the Hungarian-made Automated Telescope Network. It’s known as a ‘hot Jupiter,’ a gas giant similar to our neighboring planet Jupiter, but with a radius twice as large. This hot Jupiter hugs closely in orbit to its host star, about three percent the distance from the Earth to the Sun. Its orbital period — what we consider a year here on Earth — is only 2.15 days, and this proximity to the star scorches it with both long and short wave radiation.
The main motivation for the scientists’ interest in studying hot Jupiters is their pursuit of the mystery of the Neptunian desert, the inexplicable relative scarcity on average of intermediate-mass planets, or sub-Jupiters, with short orbital periods.
“One of the potential explanations is that maybe the planets are losing their mass,” Zhang offered. “If we can capture planets in the process of losing their atmosphere, then we can study how fast the planet is losing their mass and what are the mechanisms that cause their atmosphere to escape from the planet. It's good to have some examples to see like the HAT-P-32b process in action.”
The light analyzed in the study comes from the star HAT-P-32 A. It’s slightly hotter and similar in size to our own sun. The analyzed light is not just straight starlight. As the planet passes in front of the star, for just a couple of hours the starlight gets filtered the most by the planet’s gassy atmosphere. This filtering, called absorption, reveals features of the transiting planet, in this case huge outflows of helium when the spectra were analyzed.
Zhang and colleagues used a technique called transmission spectroscopy to separate the starlight into its component frequencies, like a prism separates sunlight into a rainbow spectrum. Gaps in the spectrum indicate light being absorbed by elements in the gaseous atmosphere of HAT-P-32b.
“What we see in our data is that when the planet is transiting the star, we see there's deeper helium absorption lines. The helium absorption is stronger than what we expect from the stellar atmosphere. This excess helium absorption should be caused by the planet’s atmosphere. When the planet is transiting, its atmosphere is so huge that it blocks part of the atmosphere that absorbs the helium line, and that causes this excess absorption. That's how we discovered the HAT-P-32b to be an interesting planet,” Zhang said.
It got more interesting as they developed 3D hydrodynamical simulations of the HAT-P-32b and host star, led by Antonija Oklopčić, Anton Pannekoek Institute for Astronomy, University of Amsterdam; and Morgan MacLeod, Institute for Theory and Computation, Harvard-Smithsonian Center for Astrophysics, Harvard University.
The models examined the interactions between the planetary outflow and stellar winds in the tidal gravitational field of the extrasolar system. The models showed columnar tails of planetary outflow both leading and trailing the planet along its orbital path with excess helium absorption even far from the transit points that matched observations. What is more, the models suggest complete loss of the atmosphere in about 4 x 10e10 Earth years.
The Stampede2 supercomputer at the Texas Advanced Computing Center.
CREDIT
TACC
“We made use of TACC's Stampede2 system's Intel Skylake nodes for our calculations,” MacLeod said. “This computation involves tracking flow as it accelerates from a slow-moving subsonic 'atmosphere' near the planet to a supersonic wind as it moves further away. The HAT-P-32b system was identified to have a large-scale outflow similar in size to the planet's orbit around the star. Taken together, these requirements suggest the need for a stable, high-accuracy algorithm for solving three-dimensional gas dynamics.”
The modelers utilized the Athena++ hydrodynamic software and a custom problem setup to do their calculation on Stampede2. With it they solve the equations of gas dynamics in a rotating frame of reference that matches the planet's orbital motion. Athena++ is a Eulerian code -- the flow is discretized with volume elements -- and they used nested layers of mesh refinement to capture the large-scale star-planet system along with the much smaller scale of the atmosphere near the planet's surface.
“Using the TACC HPC systems is a joy,” MacLeod said. “A few things go into this -- the first, and most important is the level of support. Whenever I have a problem, I can call the support line, get help, and get back to doing the science that I am best at. Secondly, the vast majority of my time goes into developing and validating model results, rather than running a single, full-scale calculation. The TACC systems are incredibly well set up for this reality, and it hugely speeds up the pace of development. Being able to run test calculations through the development queues or submit larger calculations of a range of sizes in the lead up to an eventual final model is crucial and effective in these environments.”
Looking ahead, the scientists hope to continue to develop sophisticated 3D models that capture effects such as atmospheric mixing of gases and even winds within the atmosphere on more distant worlds hundreds and even thousands of light years away.
“Now is the time to have supercomputers with the computational power to make this happen," Zhang said. "We need the computers to make real predictions based on recent advances in the theory and to explain the data. Supercomputers bridge the model and the data."
“The best thing we can do is watch the night sky and try to recreate what we see through computer modeling," MacLeod concluded. "Our universe is complicated. This means we need to have access to the absolute best supercomputing systems."
The study, Giant tidal tails of helium escaping the hot Jupiter HAT- P-32 b, was published June 7, 2023, in the journal Science Advances. The study authors are Zhoujian Zhang of UCSC; Caroline V. Morley, Michael Gully-Santiago, Jessica Luna, Quang H. Tran, Daniel M. Krolikowski, William D. Cochran, Brendan P. Bowler, Michael Endl, Gudmundur Stefánsson, Benjamin M. Tofflemire, Gregory R. Zeimann of UT Austin; Morgan MacLeod of Harvard University; Antonija Oklopčić of University of Amsterdam; Joe P. Ninan of Tata Institute of Fundamental Research; Suvrath Mahadevan of The Pennsylvania State University; Andrew Vanderburg of MIT. Funding came from the NASA Exoplanets Research Program grant number 80NSSC20K0257; National Science Foundation grant 2108801; NASA Hubble Fellowship grants HST-HF2- 51522.001-A. Support also came from NSF grants AST-1006676, AST-1126413, AST-1310875, AST-1310885, AST 2009889, AST 2009982, ATI 2009955, and AAG 2108512 and the Heising-Simons Foundation via grant 2017- 0494.
JOURNAL
Science Advances
METHOD OF RESEARCH
Computational simulation/modeling
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Giant tidal tails of helium escaping the hot Jupiter HAT-P-32 b
How does “MAD” accretion form around a black hole?
IMAGE: AN ILLUSTRATION OF THE BLACK HOLE X-RAY BINARY MAXI J1820+070 WITH A MAGNETICALLY ARRESTED DISK FORMED AROUND THE BLACK HOLE view more
CREDIT: YOU BEI
An international scientific team has revealed for the first time the magnetic field transport processes in the accretion flow of a black hole and the formation of a "MAD"—a magnetically arrested disk—in the vicinity of a black hole.
The researchers made the discovery while conducting multi-wavelength observational studies of an outburst event of the black hole X-ray binary MAXI J1820+070, using Insight-HXMT, China's first X-ray astronomical satellite, as well as multiple telescopes.
Key to their discovery was the observation that the radio emission from the black hole jet and the optical emission from the outer region of the accretion flow lag behind the hard X-rays from the hot gas in the inner region of the accretion flow (i.e., the hot accretion flow) by about eight days and 17 days, respectively.
These findings were published in Science on Aug. 31.
The study was led by Assoc. Prof. YOU Bei from Wuhan University, Prof. CAO Xinwu from Zhejiang University and Prof. YAN Zhen from the Shanghai Astronomical Observatory (SHAO) of the Chinese Academy of Sciences.
The process of a black hole capturing gas is known as "accretion", and the gas falling into the black hole is referred to as an accretion flow. The viscous processes within the accretion flow effectively release gravitational potential energy, with a portion of the energy being converted into multi-wavelength radiation. This radiation can be observed by ground-based and space telescopes, allowing us to "see" the black hole.
However, there are "unseen" magnetic fields around the black hole. As the black hole accretes gas, it also drags the magnetic field inwards. Previous theories suggested that as the accreting gas continuously brings in weak external magnetic fields, the magnetic field progressively strengthens towards the inner region of the accretion flow. The outward magnetic force on the accretion flow increases and counteracts the inward gravitational pull from the black hole. Therefore, in the inner region of the accretion flow near the black hole, when the magnetic field reaches a certain strength, the accreted matter becomes trapped by the magnetic field and cannot freely fall into the black hole. This phenomenon is known as a magnetically arrested disk.
The MAD theory was proposed many years ago and has successfully explained some observational phenomena related to black hole accretion. However, no direct observational evidence for the existence of a MAD was available, and MAD formation and magnetic transport mechanisms remained mysteries.
In addition to the supermassive black holes at the centers of nearly every galaxy, there are also many more stellar-mass black holes in the universe. Astronomers have detected stellar-mass black holes in many binary star systems in the Milky Way. These black holes generally have a mass about ten times that of the Sun. Most of the time, these black holes are in a quiescent state, emitting extremely weak electromagnetic radiation. However, they occasionally enter an outburst period that can last for several months or even years, producing bright X-rays. As a result, these types of binary star systems are often referred to as black hole X-ray binaries.
In this study, the researchers performed a multi-wavelength data analysis of the outburst of the black hole X-ray binary MAXI J1820+070. They observed that the hard X-ray emission exhibited a peak that was followed by a peak in radio emission eight days later. Such a long delay between radio emission from the jet and the hard X-rays from the hot accretion flow is unprecedented.
These observations indicate that the weak magnetic field in the outer region of the accretion disk is carried into the inner region by the hot gas, and the radial extent of the hot accretion flow rapidly expands as the accretion rate decreases. The greater the radial extent of the hot accretion flow, the greater the increase in the magnetic field. This leads to a rapid strengthening of the magnetic field near the black hole, resulting in the formation of a MAD approximately eight days after the peak of the hard X-ray emission.
"Our study for the first time reveals the process of magnetic field transport in the accretion flow and the process of MAD formation in the vicinity of the black hole. This represents the direct observational evidence for the existence of a magnetically arrested disk," said Assoc. Prof. YOU Bei, first author and co-corresponding author of the study.
Additionally, the research team observed an unprecedented delay (about 17 days) between the optical emission from the outer region of the accretion flow and the hard X-rays from the hot accretion flow. Through numerical simulations of the outburst of the black hole X-ray binary, it was discovered that as the outburst approaches the end, the irradiation of hard X-rays causes more accreting material from the far outer region to fall towards the black hole due to instability. This leads to an optical flare in the outer region of the accretion flow, with the peak occurring about 17 days after the peak of the hard X-rays from the hot accretion flow.
"Due to the universality of black hole accretion physics, where accretion processes for black holes of different mass scales follow the same physical laws, this research will advance the understanding of scientific questions related to large-scale magnetic field formation, jet powering, and acceleration mechanisms for accreting black holes of different mass scales," said Prof. CAO Xinwu, co-corresponding author of the study.
Similar phenomena to those observed in MAXI J1820+070 are expected to be observed in more accreting black hole systems in the near future, noted Prof. YAN Zhen, co-corresponding author of the study.
Multi-wavelength light curves (showing the change in brightness over time) of the black hole X-ray binary MAXI J1820+070
Schematic representation of accretion flow, magnetic field, and jet evolution
CREDIT
SHAO
JOURNAL
Science
ARTICLE TITLE
Observations of a black hole x-ray binary indicate formation of a magnetically arrested disk
Unprecedented gamma-ray burst explained by long-lived jet
First large-scale numerical simulation of black hole-neutron star merger matches puzzling observations
Peer-Reviewed PublicationVIDEO: FULL SIMULATION OF THE LARGE-SCALE EVOLUTION OF A JET FROM A BLACK HOLE-NEUTRON STAR MERGER. view more
CREDIT: ORE GOTTLIEB/NORTHWESTERN UNIVERSITY
Last year, Northwestern University researchers reported new observational evidence that long gamma-ray bursts (GRBs) can result from the merger of a neutron star with another compact object (either another neutron star or black hole) — a finding that was previously believed to be impossible.
Now, another Northwestern team offers a potential explanation for what generated the unprecedented and incredibly luminous burst of light.
After developing the first numerical simulation that follows the jet evolution in a black hole-neutron star merger out to large distances, the astrophysicists discovered that the post-merger black hole can launch jets of material from the swallowed neutron star.
But the key ingredients are the mass of the violent whirlpool of gas (or accretion disk) surrounding the black hole and the strength of the disk’s magnetic field. In massive disks, when the magnetic field is strong, the black hole launches a short-duration jet that is much brighter than anything ever seen in observations. When the massive disk has a weaker magnetic field, however, the black hole launches a jet with the same luminosity and long duration as the mysterious GRB (dubbed GRB211211A) spotted in 2021 and reported in 2022.
Not only does the new discovery help explain the origins of long GRBs, it also gives insight into the nature and physics of black holes, their magnetic fields and accretion disks.
The study will be published Thursday (Aug. 31) in the Astrophysical Journal.
“So far, no one else has developed any numerical works or simulations that consistently follow a jet from the compact-object merger to the formation of the jet and its large-scale evolution,” said Northwestern’s Ore Gottlieb, who co-led the work. “The motivation for our work was to do this for the first time. And what we found just so happened to match observations of GRB211211A.”
“Neutron-star mergers are a captivating multi-messenger phenomena, which result in both gravitational and electromagnetic waves,” said Northwestern’s Danat Issa, who co-led the work with Gottlieb. “However, simulating these events poses a challenge due to the vast spatial and temporal scale separations involved as well as the diverse physics operating across these scales. For the first time, we have succeeded in comprehensively modeling the entire sequence of the neutron star merger process.”
During the research, Gottlieb was a CIERA Fellow at Northwestern’s Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA); now he is a Flatiron Research Fellow at the Flatiron Institute’s Center for Computational Astrophysics. Issa is a graduate student in the Department of Physics and Astronomy at Northwestern’s Weinberg College of Arts and Sciences and member of CIERA. Issa is advised by paper co-author Alexander Tchekhovskoy, an associate professor of physics and astronomy at Weinberg and member of CIERA.
Curious kilonova
When astronomers first spotted GRB211211A in December 2021, they initially assumed that the 50-second-long event was generated from the collapse of a massive star. But, as they examined the long GRB’s late-time emission, called the afterglow, they uncovered evidence of a kilonova, a rare event that only occurs after the merger of a neutron star with another compact object.
The finding (published in Nature in December 2022) upended the long-established, long-accepted belief that only supernovae could generate long GRBs.
“GRB 211211A reignited interest in the origin of long-duration GRBs that are not associated with massive stars, but likely originating from compact binary mergers,” Gottlieb said.
From pre-merger to long GRB
To further reveal what occurs during compact-merger events, Gottlieb, Issa and their collaborators sought to simulate the whole process — from before the merger all the way through to the end of the GRB event, when the GRB-producing jets shut off. Because it is such an incredibly computationally expensive feat, the entire scenario had never been modeled before. Gottlieb and Issa overcame that challenge by dividing the scenario into two simulations.
First, the researchers ran a simulation of the pre-merger phase. Then, they took the output from the first simulation and plugged it into the post-merger simulation.
“Because the space-time used by the two simulations is different, this remap was not as straightforward as we had hoped, but Danat figured it out,” Tchekhovskoy said.
“The daisy chaining of the two simulations allowed us to make the computation much less expensive,” Gottlieb said. “The physics is very complicated in the pre-merger stage because there are two objects. It gets much simpler after the pre-merger because there is only one black hole.”
In the simulation, the compact objects first merged to create a more massive black hole. The black hole’s intense gravity pulled the now-destroyed neutron star’s debris toward it. Before the debris fell into the black hole, some of the debris first swirled around the black hole as an accretion disk. In the configuration studied, the emerging disk was particularly massive with one-tenth the mass of our sun. Then, when the mass fell into the black hole from the disk, it powered the black hole to launch a jet that accelerated to near light speed.
Disk properties matter
A surprise emerged as the researchers adjusted the strength of the massive disk’s magnetic field. Whereas a strong magnetic field resulted in a short, incredibly bright GRB, a weak magnetic field generated a jet that matched observations of long GRBs.
“The stronger the magnetic field, the shorter is its lifetime,” Gottlieb said. “Weak magnetic fields produce weaker jets that the newly formed black hole can sustain for a longer time. A key ingredient here is the massive disk that can maintain, together with weak magnetic fields, a GRB consistent with observations and comparable to the luminosity and long duration of GRB211211A. Although we found this specific binary system to give rise to a long GRB, we also expect that other binary mergers that produce massive disks will lead to a similar outcome. It’s simply a question of the post-merger disk mass.”
Of course, “long” is relative in this scenario. GRBs are divided into two classes. GRBs with durations less than two seconds are considered short. If a GRB is two seconds or longer, then it’s considered long. Even events this brief are still exceptionally difficult to model.
“A major portion of this disk material ultimately gets consumed by the black hole, with the whole process lasting mere seconds,” Issa said. “Here lies the main challenge: It is very difficult to capture the evolution of these mergers, using simulations on supercomputers, over a span of several seconds.”
Next up: Neutrinos
Now that Gottlieb and Issa have successfully and comprehensively modeled the full sequence of the merger, they are excited to continue to update and improve their models.
“My current efforts are directed towards enhancing the physical accuracy of the simulations,” Issa said. “This involves the incorporation of neutrino cooling, a vital component that holds the potential to significantly influence the dynamics of the merger process. Furthermore, the inclusion of neutrinos serves as a critical step towards achieving a more accurate assessment of the nuclear composition of the material ejected as a consequence of these mergers. Through this approach, my goal is to provide a more comprehensive and accurate picture of neutron star mergers.”
The study, “Large-scale evolution of seconds-long relativistic jets from black hole-neutron star mergers,” was supported by NASA, the National Science Foundation and the U.S. Department of Energy.
GRB 211211A’s location, circled in red, captured using three filters on Hubble’s Wide Field Camera 3.
CREDIT
NASA, ESA, Rastinejad et al. (2022)
JOURNAL
The Astrophysical Journal
METHOD OF RESEARCH
Computational simulation/modeling
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Large-scale evolution of seconds-long relativistic jets from black hole-neutron star mergers
New giant planet evidence of possible planetary collisions
IMAGE: IMPACT SIMULATION view more
CREDIT: JINGYAO DOU
A Neptune-sized planet denser than steel has been discovered by an international team of astronomers, who believe its composition could be the result of a giant planetary clash.
TOI-1853b's mass is almost twice that of any other similar-sized planet known and its density is incredibly high, meaning that it is made up of a larger fraction of rock than would typically be expected at that scale.
In the study, published today in Nature, scientists led by Luca Naponiello of University of Rome Tor Vergata and the University of Bristol suggest that this is the result of planetary collisions. These huge impacts would have removed some of the lighter atmosphere and water leaving a multitude of rock behind.
Senior Research Associate and co author Dr Phil Carter from Bristol’s School of Physics, explained: “We have strong evidence for highly energetic collisions between planetary bodies in our solar system, such as the existence of Earth's Moon, and good evidence from a small number of exoplanets.
“We know that there is a huge diversity of planets in exoplanetary systems; many have no analog in our solar system but often have masses and compositions between that of the rocky planets and Neptune/Uranus (the ice giants).
“Our contribution to the study was to model extreme giant impacts that could potentially remove the lighter atmosphere and water/ice from the original larger planet in order to produce the extreme density measured.
“We found that the initial planetary body would likely have needed to be water-rich and suffer an extreme giant impact at a speed of greater than 75 km/s in order to produce TOI-1853b as it is observed.”
This planet provides new evidence for the prevalence of giant impacts in the formation of planets throughout the galaxy. This discovery helps to connect theories for planet formation based on the solar system to the formation of exoplanets. The discovery of this extreme planet provides new insights into the formation and evolution of planetary systems.
Postgraduate student and co author Jingyao Dou said: “This planet is very surprising! Normally we expect planets forming with this much rock to become gas giants like Jupiter which have densities similar to water.
“TOI-1853b is the size of Neptune but has a density higher than steel. Our work shows that this can happen if the planet experienced extremely energetic planet-planet collisions during its formation.
Now the team plan detailed follow-up observations of TOI-1853b to attempt to detect any residual atmosphere and examine its composition.
Associate Professor and co author Dr Zoë Leinhardt concluded: “We had not previously investigated such extreme giant impacts as they are not something we had expected. There is much work to be done to improve the material models that underlie our simulations, and to extend the range of extreme giant impacts modelled.”
The simulations were performed using the computational facilities of the Advanced Computing Research Centre, University of Bristol. Funders include Science and Technology Facilities Council (STFC) and China Scholarship Council.
Graphic of TOI-1853b
CREDIT
Luca Naponiello
Paper:
‘A super-massive Neptune-sized planet’ by Luca Naponiello, Jingyao Dou, Zoe Leinhardt, Philip Carter et al. in Nature.
JOURNAL
Nature
METHOD OF RESEARCH
Computational simulation/modeling
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
A super-massive Neptune-sized planet
Hunting for supermassive black holes in the early universe
IMAGE: A SUPERMASSIVE BLACK HOLE (SMBH; THE SMALL BLACK DOT AT THE CENTER) ABSORBS SURROUNDING MATERIAL, WHICH FORMS A SPIRAL DISK-LIKE SHAPE AS IT FLOWS IN. THE GRAVITATIONAL ENERGY OF THE MATERIAL IS CONVERTED TO RADIATION AND EMITTED AWAY FROM THE DISK. SMBHS WITH SUCH SHINING OUTSKIRTS ARE CALLED “QUASARS”. view more
CREDIT: YOSHIKI MATSUOKA
Supermassive black holes (SMBHs) – black holes with masses exceeding a million times that of the Sun – are known to prevail in the universe today. However, it is not clear yet when, where, and how they formed during the 13.8 billion years of cosmic history. Observations in the past few decades have revealed that every galaxy harbors a SMBH in the center, and that the black hole mass is almost always one-thousandth of the host galaxy mass. This close relationship implies that galaxies and SMBHs have co-evolved together. Revealing the origin of SMBHs is thus crucial not only to understand SMBHs themselves, but also to elucidate the formation processes of galaxies, the major constituents of the visible universe.
A key to addressing this issue lies in the early universe, where the time elapse since the Big Bang (i.e., the beginning of the universe) was less than a billion years. Thanks to the finite speed of light, we can look back at the past by observing the distant universe. Did SMBHs already exist when the universe was only a billion years old or less? Is it possible for a black hole to acquire such a large mass (exceeding a million solar masses and sometimes reaching billions of solar masses) in such a short time? If so, what are the underlying physical mechanisms and conditions? In order to close in on the origin of SMBHs, we need to observe them and compare their properties with predictions from theoretical models. And in order to do so, we first need to find where they are in the sky.
We used the Subaru Telescope at the top of Maunakea, Hawaii, for the present study. One of the biggest advantages of Subaru is its widefield observing capability, which is particularly suited for our purpose. Since SMBHs do not emit light, we looked for a special class called “quasars” – SMBHs with shining outskirts where the infalling material releases gravitational energy. We observed a wide sky area equivalent to 5000 times the full moon, and successfully discovered 162 quasars residing in the early universe. In particular, 22 of them lived in the era when the universe was less than 800 million years old – the most ancient period in which quasars have been recognized to date. The large number of quasars we discovered has allowed us to determine the most fundamental measure called the “luminosity function”, which describes the space density of quasars as a function of radiation energy. We found that quasars were forming very rapidly in the early universe, while the overall shape of the luminosity function (except for the amplitude) remained unchanged over time. This characteristic behavior of the luminosity function provides strong constraints on theoretical models, which could ultimately reproduce all the observables and describe the origin of SMBHs.
On the other hand, the universe was known to have experienced a major phase transition called “cosmic reionization” in its early stage. Past observations suggest that the whole intergalactic space was ionized in this event. The source of the ionization energy is still under debate, with radiation from quasars being considered as a promising candidate. By integrating the above luminosity function, we found that quasars emit 1028 photons per second in a unit volume of 1 light-year on a side in the early universe. This is less than 1% of the photons needed to maintain the ionized state of the intergalactic space at that time, and thus indicates that quasars made only a minor contribution to cosmic reionization. Other energy sources are critically needed, which, according to other recent observations, may be the integrated radiation from massive hot stars in forming galaxies.
An example of the night-sky photograph we took with the Subaru Telescope. The tiny red dot at the center of the magnified image represents the light from a distant quasar, which existed when the universe was 800 million years old (13 billion light-years away).
CREDIT
National Astronomical Observatory of Japan
Luminosity function describes the space density (Φ on the vertical axis) as a function of radiation energy (M1450 on the horizontal axis). We plot the luminosity functions of quasars observed when the age of the universe was 0.8 (red dots), 0.9 (green diamonds), 1.2 (blue squares), and 1.5 (black triangles) billion years. The curves represent the best-fit functional forms. The space density of quasars rose steeply over time, while the shape of the luminosity function remains almost unchanged.
CREDIT
The Astrophysical Journal Letters, 949, L42, 2023
JOURNAL
The Astrophysical Journal Letters
