It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
IMAGE: RESEARCHERS USED THE ATACAMA COSMOLOGY TELESCOPE TO CREATE THIS NEW MAP OF THE DARK MATTER. THE ORANGE REGIONS SHOW WHERE THERE IS MORE MASS; PURPLE WHERE THERE IS LESS OR NONE. THE TYPICAL FEATURES ARE HUNDREDS OF MILLIONS OF LIGHT YEARS ACROSS. THE WHITISH BAND SHOWS WHERE CONTAMINATING LIGHT FROM DUST IN OUR MILKY WAY GALAXY, MEASURED BY THE PLANCK SATELLITE, OBSCURES A DEEPER VIEW. THE NEW MAP USES LIGHT FROM THE COSMIC MICROWAVE BACKGROUND (CMB) ESSENTIALLY AS A BACKLIGHT TO SILHOUETTE ALL THE MATTER BETWEEN US AND THE BIG BANG. “IT’S A BIT LIKE SILHOUETTING, BUT INSTEAD OF JUST HAVING BLACK IN THE SILHOUETTE, YOU HAVE TEXTURE AND LUMPS OF DARK MATTER, AS IF THE LIGHT WERE STREAMING THROUGH A FABRIC CURTAIN THAT HAD LOTS OF KNOTS AND BUMPS IN IT,” SAID SUZANNE STAGGS, DIRECTOR OF ACT AND PRINCETON'S HENRY DEWOLF SMYTH PROFESSOR OF PHYSICS. “THE FAMOUS BLUE AND YELLOW CMB IMAGE IS A SNAPSHOT OF WHAT THE UNIVERSE WAS LIKE IN A SINGLE EPOCH, ABOUT 13 BILLION YEARS AGO, AND NOW THIS IS GIVING US THE INFORMATION ABOUT ALL THE EPOCHS SINCE.”view more
CREDIT: ACT COLLABORATION
For millennia, humans have been fascinated by the mysteries of the cosmos.
Unlike ancient philosophers imagining the universe’s origins, modern cosmologists use quantitative tools to gain insights into the universe’s evolution and structure. Modern cosmology dates back to the early 20th century, with the development of Albert Einstein’s theory of general relativity.
Now, researchers from the Atacama Cosmology Telescope (ACT) collaboration have created a groundbreaking new image that reveals the most detailed map of dark matter distributed across a quarter of the entire sky, extending deep into the cosmos. What’s more, it confirms Einstein’s theory of how massive structures grow and bend light, over the entire 14-billion-year life span of the universe.
“We have mapped the invisible dark matter across the sky to the largest distances, and clearly see features of this invisible world that are hundreds of millions of light-years across, says Blake Sherwin, professor of cosmology at the University of Cambridge, where he leads a group of ACT researchers. “It looks just as our theories predict.”
Despite making up 85% of the universe and influencing its evolution, dark matter has been hard to detect because it doesn’t interact with light or other forms of electromagnetic radiation. As far as we know dark matter only interacts with gravity.
To track it down, the more than 160 collaborators who have built and gathered data from the National Science Foundation’s Atacama Cosmology Telescope in the high Chilean Andes observe light emanating following the dawn of the universe’s formation, the Big Bang—when the universe was only 380,000 years old. Cosmologists often refer to this diffuse light that fills our entire universe as the “baby picture of the universe,” but formally, it is known as the cosmic microwave background radiation (CMB).
The team tracks how the gravitational pull of large, heavy structures including dark matter warps the CMB on its 14-billion-year journey to us, like how a magnifying glass bends light as it passes through its lens.
“We’ve made a new mass map using distortions of light left over from the Big Bang,” says Mathew Madhavacheril, assistant professor in the Department of Physics and Astronomy at the University of Pennsylvania. “Remarkably, it provides measurements that show that both the ‘lumpiness’ of the universe, and the rate at which it is growing after 14 billion years of evolution, are just what you’d expect from our standard model of cosmology based on Einstein's theory of gravity.”
Sherwin adds, “our results also provide new insights into an ongoing debate some have called ‘The Crisis in Cosmology,’”explaining that this crisis stems from recent measurements that use a different background light, one emitted from stars in galaxies rather than the CMB. These have produced results that suggest the dark matter was not lumpy enough under the standard model of cosmology and led to concerns that the model may be broken. However, the team’s latest results from ACT were able to precisely assess that the vast lumps seen in this image are the exact right size.
“When I first saw them, our measurements were in such good agreement with the underlying theory that it took me a moment to process the results,” says Cambridge Ph.D. student Frank Qu, part of the research team. “It will be interesting to see how this possible discrepancy between different measurements will be resolved.”
“The CMB lensing data rivals more conventional surveys of the visible light from galaxies in their ability to trace the sum of what is out there,” says Suzanne Staggs, director of ACT and Henry DeWolf Smyth Professor of Physics at Princeton University. “Together, the CMB lensing and the best optical surveys are clarifying the evolution of all the mass in the universe.”
“When we proposed this experiment in 2003, we had no idea the full extent of information that could be extracted from our telescope,” says Mark Devlin, the Reese Flower Professor of Astronomy at the University of Pennsylvania and the deputy director of ACT. “We owe this to the cleverness of the theorists, the many people who built new instruments to make our telescope more sensitive, and the new analysis techniques our team came up with.”
ACT, which operated for 15 years, was decommissioned in September 2022. Nevertheless, more papers presenting results from the final set of observations are expected to be submitted soon, and the Simons Observatory will conduct future observations at the same site, with a new telescope slated to begin operations in 2024. This new instrument will be capable of mapping the sky almost 10 times faster than ACT.
The Atacama Cosmology Telescope in Northern Chile, supported by the National Science Foundation, operated from 2007-2022. The project is led by Princeton University and the University of Pennsylvania -- Director Suzanne Staggs at Princeton, Deputy Director Mark Devlin at Penn -- with 160 collaborators at 47 institutions.
CREDIT
Mark Devlin, Deputy Director of the Atacama Cosmology Telescope and the Reese Flower Professor of Astronomy at the University of Pennsylvania
Research by the Atacama Cosmology Telescope collaboration has culminated in a groundbreaking new map of dark matter distributed across a quarter of the entire sky, reaching deep into the cosmos. Findings provide further support to Einstein’s theory of general relativity, which has been the foundation of the standard model of cosmology for more than a century, and offer new methods to demystify dark matter.
CREDIT
Debra Kellner
Research by the Atacama Cosmology Telescope collaboration has culminated in a groundbreaking new map of dark matter distributed across a quarter of the entire sky, reaching deep into the cosmos. Findings provide further support to Einstein’s theory of general relativity, which has been the foundation of the standard model of cosmology for more than a century, and offer new methods to demystify dark matter.
CREDIT
Lucy Reading-Ikkanda, Simons Foundation
Learn more at https://act.princeton.edu/. This research will be presented at "Future Science with CMB x LSS," a conference running from April 10-14 at Yukawa Institute for Theoretical Physics, Kyoto University. This work was supported by the U.S. National Science Foundation (AST-0408698, AST-0965625 and AST-1440226 for the ACT project, as well as awards PHY-0355328, PHY-0855887 and PHY-1214379), Princeton University, the University of Pennsylvania, and a Canada Foundation for Innovation award. Team members at the University of Cambridge were supported by the European Research Council.
Tuesday, October 24, 2023
Biggest ever supercomputer simulation to investigate universe’s evolution Nina Massey, PA Science Correspondent Mon, 23 October 2023
Astronomers have carried out the biggest ever computer simulations, from the Big Bang to the present day, to investigate how the universe evolved.
The project, dubbed Flamingo, calculated the evolution of all components of the universe – ordinary matter, dark matter and dark energy – according to the laws of physics.
As the simulations progress, virtual galaxies and galaxy clusters emerge in detail.
Facilities such as the Euclid Space Telescope recently launched by the European Space Agency (ESA) and Nasa’s James Webb Space Telescope collect data on galaxies, quasars and stars.
Researchers hope the simulations will allow them to compare the virtual universe with observations of the real thing being captured by new high-powered telescopes.
This could help scientists understand if the standard model of cosmology – used to explain the evolution of the universe – is a good description of reality.
Flamingo research collaborator Professor Carlos Frenk, Ogden Professor of Fundamental Physics, at the Institute for Computational Cosmology, Durham University, said: “Cosmology is at a crossroads.
“We have amazing new data from powerful telescopes some of which do not, at first sight, conform to our theoretical expectations.
“Either the standard model of cosmology is flawed or there are subtle biases in the observational data.
“Our super precise simulations of the universe should be able to tell us the answer.”
Past simulations, which have been compared to observations of the universe, have focused on cold dark matter – believed to be a key component of the structure of the cosmos.
However, astronomers now say that the effect of ordinary matter, which makes up only 16% of all matter in the universe, and neutrinos, tiny particles that rarely interact with normal matter, also need to be taken into account when trying to understand the universe’s evolution.
Principal investigator Professor Joop Schaye, of Leiden University, said: “Although the dark matter dominates gravity, the contribution of ordinary matter can no longer be neglected since that contribution could be similar to the deviations between the models and the observations.”
Researchers ran simulations at a powerful supercomputer in Durham over the past two years.
The simulations took more than 50 million processor hours on the Cosmology Machine (COSMA 8) supercomputer, hosted by the Institute for Computational Cosmology, Durham University, on behalf of the UK’s DiRAC High-Performance Computing facility.
In order to make the simulations possible, the researchers developed a new code, called SWIFT, which distributes the computational work over thousands of central processing units (CPUs, sometimes as many as 65,000).
Flamingo is a project of the Virgo Consortium for cosmological supercomputer simulations. The acronym stands for full-hydro large-scale structure simulations with all-sky mapping for the interpretation of next generation observations.
Funding for the project came from the European Research Council, the UK’s Science and Technology Facilities Council, the Netherlands Organisation for Scientific Research and the Swiss National Science Foundation.
The research is published in the journal Monthly Notices of the Royal Astronomical Society.
The aim is to compare the virtual universe with what we know of the real thing, including new information being captured by high-powered telescopes – which sometimes does not quite match what is expected.
This could help scientists understand if the current theory of how the universe evolved – known as the Standard Model of Cosmology – is a good description of reality.
The project, dubbed Flamingo, calculated the evolution of all components of the universe – ordinary matter, dark matter and dark energy – according to the laws of physics.
As the simulations progress, virtual galaxies and galaxy clusters emerge in detail.
Facilities such as the Euclid Space Telescope, recently launched by the European Space Agency (ESA), and Nasa’s James Webb Space Telescope collect data on galaxies, quasars and stars.
‘Cosmology is at a crossroads,’ said Flamingo research collaborator Professor Carlos Frenk, from Durham University.
‘We have amazing new data from powerful telescopes some of which do not, at first sight, conform to our theoretical expectations.
‘Either the standard model of cosmology is flawed or there are subtle biases in the observational data.
‘Our super precise simulations of the universe should be able to tell us the answer.’
Past simulations, which have been compared to observations of the universe, have focused on cold dark matter – believed to be a key component of the structure of the cosmos.
However, astronomers now say that the effect of ordinary matter, which makes up only 16% of all matter in the universe – including the Earth and everyone on it – and neutrinos, tiny particles that rarely interact with normal matter, also need to be taken into account when trying to understand the universe’s evolution.
Researchers have been running simulations at a powerful supercomputer in Durham over the past two years.
The simulations took more than 50 million processor hours on the Cosmology Machine (COSMA 8) supercomputer, hosted by the Institute for Computational Cosmology, Durham University, on behalf of the UK’s DiRAC High-Performance Computing facility.
Flamingo is a project of the Virgo Consortium for cosmological supercomputer simulations. The acronym stands for full-hydro large-scale structure simulations with all-sky mapping for the interpretation of next generation observations.
Funding for the project came from the European Research Council, the UK’s Science and Technology Facilities Council, the Netherlands Organisation for Scientific Research and the Swiss National Science Foundation.
PARIS, France – 24 November 2025 – The 6th COSPAR Symposium has concluded in Nicosia, bringing together over 300 scientists, agency leaders, and industry pioneers from 50+ countries. Hosted by the Cyprus Space Exploration Organisation (CSEO) with the support of Chief Scientist Demetris Skourides, the event consolidated COSPAR’s role as an international platform for dialogue in space science as well as Cyprus’s growing influence in the global space sector.
Key highlights included the Space Agency Leaders Roundtable, the release of the Heliophysics Guidelines, the introduction of COSPAR’s Space Exploration Roadmap, and ground-breaking scientific announcements such as that from George Spyrou, unveiling AI-driven bioinformatics discoveries for astronaut health, and from Eija Tanskanen presenting new insights on space weather risks.
Global Guidelines on “Space Weather” and Heliophysics The symposium saw the official release of the COSPAR Heliophysics Guidelines, a set of unified global principles for the scientific study of the Sun and its effects. Heliophysics is the science that studies solar and magnetospheric physics, space physics and aeronomy, and space weather, the latter posing a significant threat to modern life. A severe solar storm, on the scale of the 1859 “Carrington Event”, could today cripple power grids, knock out satellite communications and GPS, and effectively shut down the internet, causing trillions of dollars in damage and bringing global society to a standstill. To prevent such a “digital Carrington event”, coordinated global action is essential. The new guidelines, announced in Nicosia, create a “common language” for scientists and space agencies worldwide to share data, coordinate observations, and improve forecasting of these dangerous solar events. Jean-Claude Worms, COSPAR Executive Director, stated, “In an era where our reliance on technology is absolute, understanding space weather is not just an academic pursuit—it is a global necessity. These guidelines, supported by the world’s leading space science institutions, represent a critical step in building a united front to protect our planet.” The initiative was supported by a powerful consortium including China’s National Space Science Center, the Space Studies Board of the US’ National Academies of Science, Engineering, and Medicine, the Solar Physics Division of the American Astronomical Society (SPD-AAS), the Space Physics and Aeronomy Section of the American Geophysical Union (SPA-AGU), the Cyprus Space Exploration Organisation (CSEO), and Italy’s INAF, with NASA and the Canadian Space Agency also evaluating adoption.
C-SpaRC Discoveries: Unlocking the Secrets of Space Hazards The Bioinformatics Workshop and Press Conference was a media spotlight for C-SpaRC, COSPAR’s International Space Innovation Centre in Cyprus. Eija Tanskanen, Director of the Sodankylä Geophysical Observatory, one of the C-SpaRC consortium partners, presented a discovery that challenges conventional wisdom on space weather. Her research demonstrated that the most severe space hazard effects occur not during the peak of the 11-year solar cycle (sunspot maxima), but during its declining phase, with impacts that are more regional and stronger than previously understood. This discovery has profound implications for the safety of satellites, power grids, and the planning of future human exploration missions. George Spyrou, the Bioinformatics ERA Chair at the Cyprus Institute of Neurology & Genetics, also a C-SpaRC consortium partner, revealed how his team is pioneering “computational drug repurposing”. He explained how they use AI to analyze genetic changes caused by microgravity in human heart and muscle cells, successfully identifying existing medicines that can be repurposed to protect astronauts from health risks like cardiovascular damage and muscle atrophy, with direct applications for patients on Earth. He also unveiled the H-SPAR DB, a powerful human spaceflight database and analysis platform developed entirely in Cyprus to accelerate global research in space health.
Industry, Innovation, MoUs and Public Engagement The week showed COSPAR fulfilling its role as a dynamic platform for space scientists worldwide to exchange knowledge and collaborate without barriers. The Symposium fostered global partnerships, with landmark MoUs signed between CSEO and Japan’s IHI Corporation, focusing on satellite-enabled technology—VHF Data Exchange System for sustainable shipping, and between CSEO and India’s Pixxel, for jointly developing advanced Earth Observation solutions for the European Union market. This transformed the discussions of the Symposium into concrete, high-value collaborations, underscoring the event’s role as a true nexus for global space innovation and business. Public engagement was a cornerstone, with the well-attended Nicosia Space Science Street Festival and a Public Outreach and Education Weekend of hands-on workshops, empowering educators and inspiring future scientists. At the Closing Ceremony COSPAR medals were awarded to CSEO President George A. Danos and Chief Scientist Demetris Skourides, recognizing their leadership. COSPAR Executive Director Jean-Claude Worms highlighted the symposium’s success in advancing space science and collaboration. The Symposium served as a fertile ground for forging collaborations that will directly impact the future of the global space economy and reinforce Cyprus’s role as an international innovation hub. The Symposium concluded with a handover to Italy for the 46th COSPAR Scientific Assembly in Florence, Italy, 1-9 August 2026, marking the continued momentum of global space innovation. For more details, contact: leigh.fergus@cosparhq.cnes.fr
About COSPAR: COSPAR, the largest international scientific society dedicated to promoting global cooperation in space research, was established in 1958. It serves as a neutral platform for scientific dialogue among scientists from around the world. Today, COSPAR comprises 46 national scientific institutions and 13 international scientific unions, with 14,000 space scientists actively participating in its activities, including attending assemblies, contributing to panels and roadmaps, and publishing in its journals. COSPAR’s core mission is to facilitate dialogue and encourage international collaboration among space stakeholders across the globe. It operates through scientific commissions, panels and task groups that encompass all disciplines of space science, from Earth and atmospheric sciences to planetary science, astrophysics, solar and space plasma physics, and life and microgravity sciences. A recent focus has been on strengthening ties between science and industry. This was achieved by forming the Committee on Industry Relations, which includes 15 leading aerospace companies worldwide. The Committee advises COSPAR on integrating industry capabilities into its activities, ensuring mutual benefits for both science and industry. COSPAR website: https://cospar.world
About CSEO: The Cyprus Space Exploration Organisation (CSEO), a leading space research institute, officially represents the country in top international organisations, including COSPAR, the International Astronomical Union (IAU) and the International Astronautical Federation (IAF). CSEO spearheaded Cyprus’s entry into the NASA Artemis Accords and the European Space Agency (ESA), starting this effort back in 2012. It coordinates the International Space Innovation Centre (C-SpaRC), one of only two COSPAR Centres of Excellence worldwide, driving a mission to promote space research, innovation, and education to position Cyprus as a key player on the global space stage, with key international partners including NASA and Lockheed Martin. Symposium website: http://www.cospar2025.org
With sincere thanks to our sponsors & partners The success of the COSPAR 2025 Symposium was made possible through the generous support of our sponsors and partners. The Local Organising Committee and COSPAR extend their deepest gratitude to: • Grand Sponsor: Lockheed Martin • Grand National Sponsor: Research & Innovation Foundation (RIF) • National Sponsor: Deputy Ministry of Tourism, Republic of Cyprus • Gold Sponsor: JAXA (Japan Aerospace Exploration Agency) • Bronze Sponsor: Northrop Grumman • Partner: Space Generation Advisory Council (SGAC) • Media Sponsor: Cyprus News Agency (CNA) • Supporters: Invest Cyprus, Euro Moon Mars, ILEWG (International Lunar Exploration Working Group
Endings and beginnings: ACT releases its final data, shaping the future of cosmology
Three papers published in JCAP presenting the sixth and final data release of the Atacama Cosmology Telescope offer a new map of the “infant” Universe, confirm the “Hubble tension,” and rule out a set of extended cosmological models.
The same area as in figure 8 of the paper, but this time showing polarization vectors overlaid on a total intensity map. Both the map and vectors are from an ACT DR6+Planck f090+f150 coadd to maximize S/N, but in polarization ACT completely dominates. The theoretical TE correlation is quite low and has a scale-dependent sign, so no clear visual correspondence between the intensity and polarization fields is expected.
Credit: the Atacama Cosmology Telescope collaboration
There’s always a touch of melancholy when a chapter that has absorbed years of work comes to an end. In the case of the Atacama Cosmology Telescope (ACT), those years amount to nearly twenty — and now the telescope has completed its mission. Yet some endings are also important beginnings, opening new paths for the entire scientific community.
The three papers just published in the Journal of Cosmology and Astroparticle Physics (JCAP) by the ACT Collaboration describe and contextualize in detail the sixth and final major ACT data release — perhaps the most important one — marking significant advances in our understanding of the Universe’s evolution and its current state.
ACT’s data clarify several key points: the measurement of the Hubble constant (the number that indicates the current rate of cosmic expansion — the Universe’s “speedometer”) obtained from observations at very large cosmological distances is confirmed, and it remains markedly different from the value derived from the nearby Universe. This is both a problem and a remarkable discovery: it confirms the so-called “Hubble tension,” which challenges the model we use to describe the cosmos.
ACT’s observations also rule out many of the so-called extended models — theoretical alternatives to the standard cosmological model. That’s another “problem,” since it narrows the range of possibilities, but it also represents a new, cleaner starting point: time to stop pursuing these models and look elsewhere.
Last but not least, ACT provides new polarization maps of the cosmic microwave background — the Universe’s “fossil light” — which complement Planck’s temperature maps, but with much higher resolution. “When we compare them, it’s a bit like cleaning your glasses,” says Erminia Calabrese, cosmologist at Cardiff University, ACT collaboration member and coordinator of one of the three papers.
The three papers published in JCAP are:
Sigurd Naess, Yilun Guan, Adriaan J. Duivenvoorden, Matthew Hasselfield, Yuhan Wang and the Atacama Cosmology Telescope collaboration - The Atacama Cosmology Telescope: DR6 maps
Thibaut Louis, Adrien La Posta, Zachary Atkins, Hidde T. Jense and the Atacama Cosmology Telescope collaboration - The Atacama Cosmology Telescope: DR6 power spectra, likelihoods and ΛCDM parameters
Erminia Calabrese, J. Colin Hill, Hidde T. Jense, Adrien La Posta and the Atacama Cosmology Telescope collaboration - The Atacama Cosmology Telescope: DR6 constraints on extended cosmological models
The sixth ACT data release was made available in March as a preprint, and the collaboration’s three official papers have now been published in JCAP following peer review. ACT is operated by the namesake collaboration, an international consortium of more than 100 researchers from universities and research institutes around the world, who have jointly authored these new studies.
Planck and ACT: “Sibling” and Complementary Telescopes
The Planck satellite, operated by the European Space Agency (ESA), was launched in 2009 with the goal of mapping the cosmic microwave background (CMB) with extremely high precision. Cosmologists often describe this radiation as the Universe’s “fossil light,” emitted during the earliest stages of cosmic evolution. Its observations allowed scientists to reconstruct the composition, age, and geometry of the primordial Universe.
Planck was a landmark mission, but it left some gaps—several of which have now been filled thanks to ACT’s work. Unlike Planck, which was a satellite in orbit, ACT is a ground-based telescope located at about 5,000 meters of altitude in Chile’s Atacama Desert. While Planck focused mainly on measuring the temperature of the CMB, ACT also observed its polarization—especially in this latest data release.
Cosmological tension confirmed
One of ACT’s most important results so far is confirming one of today’s biggest headaches in cosmology: the so-called Hubble tension.
Put simply: we know the Universe is expanding, and we can estimate its current expansion rate (we’ve also learned this expansion is accelerating) from observations. The snag is that the value inferred using data from extremely distant epochs like the CMB differs from the value obtained by observing much closer astronomical objects. “Our new results demonstrate that the Hubble constant inferred from the ACT CMB data agrees with that from Planck - not only from the temperature data, but also from the polarization, making the Hubble discrepancy even more robust," explains Colin Hill, cosmologist at Columbia University and co-lead of one of the papers This may sound like an even bigger problem, but it’s actually a crucial finding: scientists now know there really is an issue with the model we use to describe the Universe (see box: the ΛCDM model), assuming the expansion rate measured from nearby objects stays unchanged.
Extended models “fail the test”
If that weren’t enough, ACT goes further in telling us we “have a problem.” Over recent decades, precisely because of the Hubble tension, many “extended” versions of the standard model have been proposed to try to resolve the discrepancy.
In one of the three new papers, led by Calabrese, the main extended models (“there are about thirty,” she notes) were tested against the new data.
The result? “They’re gone,” she admits, adding: “We assessed them completely independently. We weren’t trying to knock them down, only to study them. And the result is clear: the new observations, at new scales and in polarization, have virtually removed the scope for this kind of exercise.”
Again, sweeping away a set of theories that aimed to fix a problem might not sound exciting. “It does shrink the theoretical ‘playground’ a bit,” Calabrese concedes. But it’s good news: it means cleaning house, narrowing the viable paths forward, and no longer spending energy on what are evidently dead ends.
Sharper maps
With this latest ACT release, scientists have obtained a much sharper image of the “infant” Universe than the one provided by Planck. “This is mainly because ACT has a larger diameter — six meters compared to Planck’s one and a half meters — and sharpness increases with mirror size,” explains Sigurd Naess of the University of Oslo, one of the paper leads. “But it's also because ACT’s images of the polarized light are much more sensitive than Planck's.’ One of the three new papers presents this new map, while another compresses these maps into angular power spectra, crucial for cosmological studies.
This doesn’t mean that Planck’s results are now obsolete. On the contrary, as Louis, points out, “the real importance of the new data is that they are complementary to the previous ones and together contribute to an extremely rich composite picture.”
Far from being the end of a project, ACT’s sixth and final data release marks a new beginning — one that will hopefully bring us closer to understanding our Universe and solving some of its biggest remaining mysteries. “We want the community to keep using and exploring these data,” says Erminia Calabrese. “We’ve provided the first interpretation, in which we have great expertise after years of work on this instrument. Now we’re delighted to hand the data over to the community for future and ongoing explorations.”
To learn more:
The Cosmic Microwave Background
The Cosmic Microwave Background (CMB) is the oldest light in the Universe — a faint glow filling the entire sky, originating about 380,000 years after the Big Bang. It is the remnant of the moment when the Universe cooled enough to become transparent, allowing light to travel freely through space. Studying it helps scientists understand what the cosmos was like and how it has evolved from its origins to the present day. Instruments that have observed it are COBE, WMAP, Planck and, more recently, ACT and the South Pole Telescope.
The ΛCDM Model
The ΛCDM model is the standard theoretical framework of cosmology — the one that best describes how the Universe is structured and how it has evolved. Λ (Lambda) stands for dark energy, a mysterious force driving the accelerated expansion of the Universe, while CDM stands for Cold Dark Matter, an invisible form of matter that does not emit light but whose gravity holds galaxies together. Along with a small amount of “normal” matter (made of atoms, like us and the stars), these components explain nearly everything we observe in the cosmos.
4 deg ×4 deg stacks of T, Qr , Ur , E and B on peaks in T for Planck SMICA (row 1), an ACT night-only coadd map (row 2), an ACT+Planck day+night coadd map (row 3), and a beam-less, noise-less simulation (row 4). These stacks are closely related to the CMB autocorrelation function, and give a simple way to illustrate the causal structure of the surface of last scattering. The outermost circle at 1.2 deg represents the autocorrelation of the 0.6 deg sound horizon at the surface of last scattering. The images are normalized to give the outer ring an amplitude of 1 (Ur and B where there is no ring use the same normalization as (Qr and E respectively). Peak detection was done separately for each map, and beam deconvolution was performed. See appendix H for details on the peak detection and stacking procedure.
Credit
The Atacama Cosmology Telescope collaboration
Average of the 4 splits for PA5 f090 night-time data covering the 3600 square degree area 255◦ > RA > 120◦,−5.5◦ < dec < 21.5◦ illustrating the deficit of large-scale power in total intensity (T) and the presence of instrumental pickup in all Stokes components. The pickup shows up as broad horizontal stripes. The color range is ±500µK in T and ±50µK in Q and U.
Credit
The Atacama Cosmology Telescope collaboration
The same maps after removing spherical harmonics coefficients with m<5; or equivalently, removing 2D Fourier modes with |â„“x|<5. The pickup is no longer visible, revealing the CMB T and E-modes, and the correlated noise structure in polarization.
An international collaboration of physicists including researchers at Washington University in St. Louis has made measurements to better understand how matter falls into black holes and how enormous amounts of energy and light are released in the process.
The scientists pointed a balloon-borne telescope called XL-Calibur at a black hole, Cygnus X-1, located about 7,000 light-years from Earth. “The observations we made will be used by scientists to test increasingly realistic, state-of-the-art computer simulations of physical processes close to the black hole,” said Henric Krawczynski, the Wilfred R. and Ann Lee Konneker Distinguished Professor in Physics and a fellow at WashU’s McDonnell Center for the Space Sciences.
The star of the show, XL-Calibur, measures the polarization of light — that is, the direction of electromagnetic field vibrations. Information about the direction of these vibrations will give scientists vital clues in determining the shape of the extremely hot gas and material violently orbiting black holes.
The observations and analysis of the data from Cygnus X-1 was published recently in The Astrophysical Journal and include the most precise measurement yet of the hard X-ray polarization from that black hole. The paper was co-authored by a collaboration incorporating many of Krawczynski’s WashU physics colleagues, including graduate student Ephraim Gau and postdoctoral research associate Kun Hu, who were very involved in the research as corresponding authors.
“If we try to find Cyg X-1 in the sky, we’d be looking for a really tiny point of X-ray light,” Gau said. “Polarization is thus useful for learning about all the stuff happening around the black hole when we can’t take normal pictures from Earth.”
This round of observations came from XL-Calibur’s trip from Sweden to Canada in July 2024.
The XL-Calibur team also recently published their measurements of polarized hard X-ray emission from the Crab pulsar and wind nebula, one of the brightest persistent sources of celestial X-rays.
Krawczynski said XL-Calibur accomplished many technical records during its 2024 flight, which included the measurements of both Cyg X-1 and the Crab pulsar.
“Collaborating with colleagues at WashU, as well as other groups in the U.S. and Japan, on XL-Calibur has been extremely rewarding,” said Mark Pearce, an XL-Calibur collaborator and a professor at KTH Royal Institute of Technology in Sweden. “Our observations of Crab and Cyg X-1 clearly show that the XL-Calibur design is sound. I very much hope that we can now build on these successes with new balloon flights.”
In the next round, the team hopes to shed light on (or capture light from) even more black holes, in addition to neutron stars, when the telescope embarks from Antarctica in 2027.
“Combined with the data from NASA satellites such as IXPE, we may soon have enough information to solve longstanding questions about black hole physics in the next few years,” added Krawczynski, the project’s primary investigator.
Saturn's moon Mimas, imaged by the Cassini spacecraft. A new study shows how such small ice moons could sustain a liquid ocean beneath an icy shell, and how that could give rise to surface features.
Credit: By NASA / JPL-Caltech / Space Science Institute - This image or video was catalogued by Jet Propulsion Laboratory of the United States National Aeronautics and Space Administration (NASA) under Photo ID: PIA12570., Public Domain, https://commons.wikimedia.org/w/index.php?curid=10371541
The outer planets of the Solar System are swarmed by ice-wrapped moons. Some of these, such as Saturn’s moon Enceladus, are known to have oceans of liquid water between the ice shell and the rocky core and could be the best places in our solar system to look for extraterrestrial life. A new study published Nov. 24 in Nature Astronomy sheds light on what could be going on beneath the surface of these worlds and provides insights into how their diverse geologic features may have formed.
“Not all of these satellites are known to have oceans, but we know that some do,” said Max Rudolph, associate professor of earth and planetary sciences at the University of California, Davis and lead author on the paper. “We’re interested in the processes that shape their evolution over millions of years and this allows us to think about what the surface expression of an ocean world would be.”
From mountains to earthquakes, Earth’s surface geology is powered by the movement and melting of rock deep inside the planet. On icy moons, geology is driven by the action of water and ice.
These worlds are heated by tidal forces from the planet they orbit. The moons orbiting a planet can interact, leading to periods of higher and lower heating. Higher heating can melt and thin the ice layer; when heating decreases, the ice gets thicker.
Rudolph and colleagues had previously looked at what happens when the ice shell gets thicker. They found that because ice has a greater volume than liquid water, freezing would put pressure on the ice shell, which could cause features such as the “tiger stripes” of Enceladus.
But what happens when the opposite happens and the ice shell melts from the bottom? That could actually cause the ocean to boil, the researchers conclude.
That’s because as ice melts into less-dense liquid water, pressure drops. Rudolph and colleagues calculated that at least on the smallest icy moons, such as Saturn’s Mimas and Enceladus, or Miranda, a moon of Uranus, the pressure could drop low enough to reach the triple point at which ice, liquid water and water vapor can all co-exist.
Images of Miranda from the Voyager 2 space probe show distinct areas of ridges and cliffs called coronae. Ocean boiling could explain how these features formed.
Mimas is less than 250 miles across and pitted with craters, including a very large crater earning it the nickname “Death Star.” It appears to be geologically dead, Rudolph said, but a wobble in its movement suggests an ocean is present. Because Mimas’ ice shell is not expected to break as a result of ice shell thinning, the presence of an ocean can be reconciled with a geologically dead surface.
The size of these moons is important. On larger ice moons, such as Titania, another moon of Uranus, the drop in pressure from melting ice would cause the ice shell to crack before the triple point for water is reached, the team calculated. The authors find that Titania’s geology could be the product of a period of ice shell thinning followed by re-thickening.
Just as geology on Earth helps us understand why our planet looks the way it does after billions of years of change, understanding geological processes on these moons can help us see why they have the features that they do, Rudolph said.
Coauthors on the paper are: Michael Manga, UC Berkeley; Alyssa Rhoden, Southwest Research Institute, Boulder; and Matthew Walker, Planetary Science Institute, Tucson. The work was supported in part by NASA.
