SPACE/COSMOS
Even black holes have bad hair days
New EHT images reveal unexpected polarization flips at M87* that are giving scientists insight into the year-by-year evolution of a supermassive black hole’s ring
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New images from the Event Horizon Telescope (EHT) collaboration have revealed a dynamic environment with changing polarization patterns in the magnetic fields of the supermassive black hole M87*. As shown in the images above, while M87*’s magnetic fields appeared to spiral in one direction in 2017, they settled in 2018 and reversed direction in 2021. The cumulative effects of this polarization change over time suggests that M87* and its surrounding environment are constantly evolving.
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Credit: Credit: EHT Collaboration
The Event Horizon Telescope (EHT) collaboration has unveiled new, detailed images of M87*, the supermassive black hole at the center of the galaxy M87, that reveal a dynamic environment with changing polarization patterns near the black hole. The new images, constructed and validated by researchers from the University of Waterloo and the Perimeter Institute for Theoretical Physics, show how the environment around the black hole may be changing more than we previously thought.
In 2017, the EHT observed a spiralling polarization pattern that is the signature of a large-scale twisted magnetic structure, confirming long-held ideas about how black holes interact with, and impact, their environments. But in 2018, the polarization all but disappeared. In 2021, the meager remnant began to spiral in the opposite direction. Astrophysicists are now wrestling with a solitary question: why?
Blockbuster movies tell us that black holes are fantastic traps where things go in and never get out. But M87* is showing us that black holes can also take energetic material from their surroundings, caught up in a powerful electromagnetic field, and launch it outward in spectacular fashion. M87*’s jet starts near the event horizon, eventually reaching 90 per cent the speed of light. These new observations offer the first tentative hint of connective tissue between the chaotic ring of plasma around the black hole and the engine at the base of this powerful jet. But exactly how black holes perform this magic trick, and what it means for the fundamental nature of gravity, is only beginning to be revealed.
“Black holes hold their mysteries tight, but we are now prying the answers from their grasp,” says Dr. Avery Broderick, a professor in the Department of Physics and Astronomy at Waterloo, and associate faculty at Perimeter Institute. “Our team at Waterloo was central to reconstructing the images from the EHT data, and determining what we can be confident is real and what could be merely an instrumental artefact. We have been at the forefront of understanding how EHT images, and especially their evolution, can reveal the astrophysical dramas unfolding on gravity's most extreme stage.”
Year after year, the EHT collaboration goes back to M87* to capture moments that show how it is evolving, knowing that each time, they will gain more insight into its long-guarded secrets.
“What’s remarkable is that while the ring size has remained consistent over the years, confirming the black hole’s shadow predicted by Einstein’s theory, the polarization pattern changes significantly,” says Dr. Paul Tiede (BSc ’15, MMath ’18, PhD ’21), an astronomer at the Center for Astrophysics | Harvard & Smithsonian, and a graduate of Waterloo and Perimeter. “This tells us that the magnetized plasma swirling near the event horizon is far from static; it’s dynamic and complex, pushing our theoretical models to the limit.”
The stability of M87*’s shadow can be taken as evidence that “black holes have no hair,” a decades-old metaphor meaning that black holes are simple geometric objects with no descriptive parameters beyond their mass, spin and charge.
“It’s one of the reasons why they're so interesting as gravitational objects. You can make very crisp, clear predictions, and all the astrophysical phenomena don't seem to matter a lot,” Broderick says. “But the stuff around it can have hair, and these magnetic fields are a striking example. We’ve had a clear sense for what kind of magnetic hairstyles should be allowed for a long time, but now we’re seeing that, like with humans, you can get a lot of different hairstyles over four years.”
Back in 2009, Broderick wrote the first paper to propose imaging M87*, exploring what we could learn about black holes, their jets and their accretion disks by observing the variability of their magnetic fields. Now, the team has taken that idea and turned it into a reality.
“That first paper talked about how the polarization of M87* could reveal information about the magnetic fields within,” Broderick says. “Now we're rapidly moving on toward extracting information about how jets accelerate and what that implies about how they're powered. This is a very exciting time for the EHT and the upcoming data we have.”
With three years of observations under their belts, the EHT has no plans to stop. Future observations will only improve as new telescopes get added to the array, making future multi-year analyses even more detailed. And if one thing is certain, it’s that M87*’s ever-changing hairdo will keep black-hole watchers coming back for more.
New images from the Event Horizon Telescope (EHT) collaboration have revealed a dynamic environment with changing polarization patterns in the magnetic fields of the supermassive black hole M87*. As shown in the images above, while M87*’s magnetic fields appeared to spiral in one direction in 2017, they settled in 2018 and reversed direction in 2021. The cumulative effects of this polarization change over time suggests that M87* and its surrounding environment are constantly evolving.
Credit
EHT Collaboration
Journal
Astronomy and Astrophysics
Method of Research
Observational study
Subject of Research
Not applicable
Article Title
Horizon-scale variability of from 2017--2021 EHT observations
Article Publication Date
16-Sep-2025
Astronomers discover rare Einstein cross with fifth image, revealing hidden dark matter
Scientists find a rare cosmic pattern that will help them learn more about the invisible matter that holds the universe together
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A rare cosmic configuration: An Einstein Cross with five points of light, instead of the usual four, has been discovered by scientists.
view moreCredit: Nicolás Lira Turpaud (ALMA Observatory) & adapted from Cox et al. 2025
When Rutgers theoretical astrophysicist Charles Keeton first saw an unusual picture shared by his colleague, he was intrigued.
“Have you ever seen an Einstein Cross with an image in the middle?” his colleague Andrew Baker asked, referring to a rarely seen cosmic configuration.
Keeton hadn’t. The implications were enormous.
“I said, well, that’s not supposed to happen,” said Keeton, the Vice Provost for Experiential Learning at Rutgers University-New Brunswick. “You can’t get a fifth image in the center unless something unusual is going on with the mass that’s bending the light.”
An “Einstein Cross” is a rarely seen cosmic configuration, in which the light from a distant galaxy is bent by the gravity of galaxies in front of it, creating four images. But the extra image in this Einstein Cross pointed to “something unusual,” which turned out to be a massive, hidden halo of dark matter. The existence of this invisible structure could only be inferred through careful computer modeling and analysis.
The discovery, made by an international team that includes Keeton, Baker and Rutgers graduate student Lana Eid, is now being published in The Astrophysical Journal.
Dark matter makes up most of the matter in the universe, but it can’t be seen directly. “We only know it’s there because of how it affects the things we can see, like the way it bends light from distant galaxies,” said Baker, a Distinguished Professor in the Department of Physics and Astronomy in the School of Arts and Sciences and a co-author of the study. “This discovery gives us a rare chance to study that invisible structure in detail.”
The first step toward that discovery was taken in France.
“We were like, ‘What the heck?’” said Pierre Cox, a French astronomer, Research Director at the French National Centre for Scientific Research and the study’s lead author, who first spotted the anomaly in data from the Northern Extended Millimeter Array (NOEMA) of radio telescopes in the French Alps.
“It looked like a cross, and there was this image in the center,” Cox said. “I knew I had never seen that before.”
The team was studying a distant, dusty galaxy called HerS-3. Using NOEMA and the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, they saw that the light from HerS-3 split into five rather than four images. At first, they thought it might be a glitch in the data. But the fifth image wouldn’t go away.
“We tried to get rid of it,” Cox said. “We thought it was a problem with the instrument. But it was real.”
Computer modeling of the gravitational lens by Keeton and Eid showed that the four visible foreground galaxies causing the gravitational bending couldn’t explain the details of the five-image pattern. Only with the addition of a large, invisible mass, in this case, a dark matter halo, could the model match the observations.
“We tried every reasonable configuration using just the visible galaxies, and none of them worked,” said Keeton, also a professor in the Department of Physics and Astronomy and a co-author of the study. “The only way to make the math and the physics line up was to add a dark matter halo. That’s the power of modeling. It helps reveal what you can’t see.”
The unusual configuration doesn’t just look cool: the scientists said it’s scientifically valuable. The lensing effect magnifies the background galaxy, allowing astronomers to study its structure in greater detail than usual. It also offers a rare chance to learn about the dark matter that surrounds the foreground galaxies.
“This system is like a natural laboratory,” Cox said. “We can study both the distant galaxy and the invisible matter that’s bending its light.”
Eid, a Rutgers graduate student pursuing her doctoral degree and a co-author of the study, said her involvement in the research project has been exciting from beginning to end.
“I was thrilled to join this project as a graduate student, especially since it involved a fascinating lensing system that grew more intriguing as our models evolved,” Eid said. “Collaborating across continents and time zones taught me the value of diverse expertise and research styles in fully understanding a new discovery.”
The team has even predicted that more features, such as outflowing gas from the galaxy, could be visible in future observations. If those predictions are confirmed, it would be a powerful validation of their models. If not, it would still teach them something new.
“This is a falsifiable prediction,” Keeton said. “If we look and don’t see it, we’ll have to go back to the drawing board. That’s how science works.”
Baker said the discovery was critically enabled by both international collaboration and U.S. federal support for science. “ALMA in Chile and the Very Large Array (VLA) in New Mexico are supported by the National Science Foundation, and the Hubble Space Telescope is supported by NASA; all played vital roles in this work,” he said. “We hope they will continue to enable such discoveries well into the future.”
Explore more of the ways Rutgers research is shaping the future
Journal
The Astrophysical Journal
Method of Research
Observational study
Subject of Research
Not applicable
Article Title
HerS-3: An Exceptional Einstein Cross Reveals a Massive Dark Matter Halo
Article Publication Date
16-Sep-2025
NYUAD scientists use AI to forecast harmful solar winds days in advance
Breakthrough improves early warnings to protect satellites and power grids
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Courtesy of NASA/SDO and the AIA, EVE, and HMI science teams
view moreCredit: Courtesy of NASA/SDO and the AIA, EVE, and HMI science teams
Scientists at NYU Abu Dhabi (NYUAD) have developed an artificial intelligence (AI) model that can forecast solar wind speeds up to four days in advance, significantly more accurately than current methods. The study is published in The Astrophysical Journal Supplement Series.
Solar wind is a continuous stream of charged particles released by the Sun. When these particles speed up, they can cause “space weather” events that disrupt Earth's atmosphere and drag satellites out of orbit, damage their electrons, and interfere with power grids. In 2022, a strong solar wind event caused SpaceX to lose 40 Starlink satellites, showing the urgent need for better forecasting.
The NYUAD team, led by Postdoctoral Associate Dattaraj Dhuri and Co-Principal Investigator at the Center for Space Science (CASS) Shravan Hanasoge, trained their AI model using high-resolution ultraviolet (UV) images from NASA’s Solar Dynamics Observatory, combined with historical records of solar wind. Instead of analyzing text, like today’s popular AI language models, the system analyzes images of the Sun to identify patterns linked to solar wind changes. The result is a 45 percent improvement in forecast accuracy compared to current operational models, and a 20 percent improvement over previous AI-based approaches.
“This is a major step forward in protecting the satellites, navigation systems, and power infrastructure that modern life depends on,” said Dhuri, lead author of the study. “By combining advanced AI with solar observations, we can give early warnings that help safeguard critical technology on Earth and in space.”
The breakthrough demonstrates how AI can solve one of space science’s toughest challenges: predicting the solar wind. With more reliable forecasts, scientists and engineers can better prepare for space weather events, strengthening resilience against disruptions to critical infrastructure.
NYU Abu Dhabi has established more than 90 faculty labs and projects, producing over 9,200 internationally recognized research publications. Times Higher Education ranks NYU among the world’s top 35 universities, making NYUAD the highest globally ranked university in the UAE.
Journal
The Astrophysical Journal Supplement Series
Method of Research
Observational study
Subject of Research
Not applicable
Article Title
A Multimodal Encoder–Decoder Neural Network for Forecasting Solar Wind Speed at L1
Article Publication Date
18-Sep-2025
Mapping the Universe, faster and with the same accuracy
A new JCAP study tests an “emulator” to reconstruct the large-scale structure of the cosmos
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Two ‘fans’ corresponding to the two main areas DESI has observed, above and below the plane of our Milky Way (see this map). DESI is mounted on the U.S. National Science Foundation Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory (KPNO), a Program of NSF NOIRLab. DESI has made the largest 3D map of our Universe to date and uses it to study dark energy. Earth is at the center of the two fans, where bluer points indicate more distant objects. This is a still from an animated rotation of the DESI Year-3 data map.
view moreCredit: DESI Collaboration/DOE/KPNO/NOIRLab/NSF/AURA/R. Proctor https://kpno.noirlab.edu/images/noirlab2512ab/
Jf you think a galaxy is big, compare it to the size of the Universe: it’s just a tiny dot which, together with a huge number of other tiny dots, forms clusters that aggregate into superclusters, which in turn weave into filaments threaded with voids—an immense 3D skeleton of our Universe.
If that gives you vertigo and you’re wondering how one can understand or even “see” something so vast, the answer is: it isn’t easy. Scientists combine the physics of the Universe with data from astronomical instruments and build theoretical models, such as EFTofLSS (Effective Field Theory of Large-Scale Structure). Fed with observations, these models describe the “cosmic web” statistically and allow its key parameters to be estimated.
Models like EFTofLSS, however, demand a lot of time and computing resources. Since the astronomical datasets at our disposal are growing exponentially, we need ways to lighten the analysis without losing precision. This is why emulators exist: they “imitate” how the models respond, but operate much faster.
Since this is a kind of “shortcut,” what’s the risk of losing accuracy? An international team including, among others, INAF (Italy), The University of Parma (Italy) and the University of Waterloo (Canada) has published in the Journal of Cosmology and Astroparticle Physics (JCAP) a study testing the emulator Effort.jl, which they designed. It shows that Effort.jl delivers essentially the same correctness as the model it imitates—sometimes even finer detail—while running in minutes on a standard laptop instead of a supercomputer.
“Imagine wanting to study the contents of a glass of water at the level of its microscopic components, the individual atoms, or even smaller: in theory you can. But if we wanted to describe in detail what happens when the water moves, the explosive growth of the required calculations makes it practically impossible,” explains Marco Bonici, a researcher at the University of Waterloo and first author of the study. “However, you can encode certain properties at the microscopic level and see their effect at the macroscopic level, namely the movement of the fluid in the glass. This is what an effective field theory does, that is, a model like EFTofLSS, where the water in my example is the Universe on very large scales and the microscopic components are small-scale physical processes.”
The theoretical model statistically explains the structure that gives rise to the data collected: the astronomical observations are fed to the code, which computes a “prediction.” But this requires time and substantial compute. Given today’s data volume—and what is expected from surveys just begun or coming soon (such as DESI, which has already released its first batch of data, and Euclid)—it’s not practical to do this exhaustively every time.
“This is why we now turn to emulators like ours, which can drastically cut time and resources,” Bonici continues. An emulator essentially mimics what the model does: its core is a neural network that learns to associate the input parameters with the model’s already-computed predictions. The network is trained on the model’s outputs and, after training, can generalize to combinations of parameters it hasn’t seen. The emulator doesn’t “understand” the physics itself: it knows the theoretical model’s responses very well and can anticipate what it would output for a new input. Effort.jl’s originality is that it further reduces the training phase by building into the algorithm knowledge we already have about how predictions change when parameters change: instead of making the network “re-learn” these, it uses them from the start. Effort.jl also uses gradients—i.e., “how much and in which direction” predictions change if you tweak a parameter by a tiny amount—another element that helps the emulator learn from far fewer examples, cutting compute needs and allowing it to run on smaller machines.
A tool like this needs extensive validation: if the emulator doesn’t know the physics, how sure are we that its shortcut yields correct answers (i.e., the same ones the model would give)? The newly published study answers exactly this, showing that Effort.jl’s accuracy—on both simulated and real data—is in close agreement with the model. “And in some cases, where with the model you have to trim part of the analysis to speed things up, with Effort.jl we were able to include those missing pieces as well,” Bonici concludes. Effort.jl thus emerges as a valuable ally for analyzing upcoming data releases from experiments like DESI and Euclid, which promise to greatly deepen our knowledge of the Universe on large scales.
The study “Effort.jl: a fast and differentiable emulator for the Effective Field Theory of the Large Scale Structure of the Universe” by Marco Bonici, Guido D’Amico, Julien Bel and Carmelita Carbone is available in the Journal of Cosmology and Astroparticle Physics (JCAP).
Journal
Journal of Cosmology and Astroparticle Physics
Method of Research
Data/statistical analysis
Article Title
Effort.jl: a fast and differentiable emulator for the Effective Field Theory of the Large Scale Structure of the Universe
Article Publication Date
16-Sep-2025
$4M grant from the John Templeton Foundation funds a new frontier in cosmology
A team that includes astrophysicists, computer scientists, artists and philosophers from USC, UC Riverside and Carnegie Observatories, embarks on an ambitious project to better understand our universe — and maybe even knowledge itself.
image:
Illuminating the Dark. Mysterious dark matter and neutrinos, formed moments after the Big Bang, are the focus of a new cosmological collaboration between USC, UC Riverside and the Carnegie Science Observatories.
view moreCredit: Martzi C. Campos/USC School of Cinematic Arts
Only about 5% of the universe consists of particles and forces well understood by modern physics. The rest remains a puzzle — one that involves dark matter, an invisible substance that shapes galaxies and cosmic structures, as well as ubiquitous but poorly understood particles called neutrinos, which were produced moments after the Big Bang.
With a $4 million grant from the John Templeton Foundation, a team of scholars from USC, the University of California, Riverside, and the Carnegie Science Observatories will establish a research hub to better understand these mysterious components of the cosmos.
The new Lyman-Alpha forest Research Collaboration (LARC) will develop cutting-edge computer models to simulate the birth of structure in the universe, testing different theories about how galaxies form. Comparing these computer-grown models of the universe to observations of the real thing will help reveal quantum properties of the universe’s hidden constituents, including dark matter and neutrino particles.
Vera Gluscevic, associate professor of physics and astronomy at the USC Dornsife College of Letters, Arts and Sciences, will serve as the collaboration lead with Simeon Bird, associate professor of astrophysics at UC Riverside, as co-lead.
“At its core, LARC is designed to pursue the deepest questions about our universe and the essence of human knowledge: What is the fundamental nature of matter? What forces shape physical reality? What is the meaning of ‘discovery’ when AI and simulation guide the pursuit of truth?” says Gluscevic.
Bird says the collaboration assembles a uniquely qualified group of scholars to tackle these questions. “The most exciting part is the team, experts in a vast range of disciplines, including theoretical and observational astrophysics, philosophy, computer science, and even interactive data visualization” he says. “I am especially excited to work with computer scientists to make better simulations of the Universe, which will help us understand where it comes from and what it’s made of.”
To boldly go …
Among the main goals of the LARC team is to use pioneering observations of hydrogen gas in space, created by scientists Drew Newman and Gwen Rudie at Carnegie Observatories, to trace dark matter. “Thanks to new observations with large telescopes, we can now map the three-dimensional structure of intergalactic gas. With the LARC team, we’ll create new ways to use these exciting maps to learn about the hidden universe,” said Newman.
LARC also includes Aiichiro Nakano, professor of computer science, physics and astronomy, and quantitative and computational biology at USC Dornsife and the USC Viterbi School of Engineering, and Christian Shelton, professor of computer science and engineering at UC Riverside. Both use artificial intelligence techniques to recognize useful patterns in computer simulations, and speed them up. This enables astrophysicists to compare simulations to real data collected by telescopes and space missions.
In doing so, they raise an important philosophical question, one which the group also plans to tackle.
Historically, scientific understanding meant formulating theories simple enough to be grasped and explained by humans. Now, the sheer volume and complexity of astronomical data challenge this traditional approach, as many insights come from computer-generated models beyond direct human intuition. What does it mean to “understand” the universe when our knowledge comes from computer-generated models?
To dig into this conundrum, a team of philosophers, led by Dmitri Gallow, associate professor of philosophy at USC Dornsife, will examine how new scientific methods such as these may change our understanding of how we produce scientific conclusions and generate knowledge.
“Using AI to understand a system as complex as the universe poses significant rewards — but also significant risks,” Gallow says. “We need to think carefully about how to responsibly learn from AI.”
The art of science
The public will get a chance to try their hand at this cosmic exploration, as well. Martzi Campos, assistant professor of cinematic arts, and game lab research associate Sean Bouchard, both with the USC School of Cinematic Arts, will produce a 3D interactive visual, which will be displayed in the Visualization Lab on the Carnegie Observatories campus, as well as educational games for the public using the hub’s work as inspiration.
The wide scope of this project is in keeping with the ambitions of John Templeton himself, a maverick investor who launched the foundation with the aim of funding advances in scientific discovery and inspiring awe and wonder for the universe.
“Understanding the fundamental nature of dark matter and neutrino particles would present a seismic advance in science, likely opening whole new directions of research in particle physics and cosmology,” Gluscevic says. “And, if we can help redefine the formal process of ‘discovery’ in the era of AI and computer simulation, we may enable future research to proceed on firmer ground and at greater speed than ever.”
Reconsidering the cosmological constant
UChicago astrophysicists’ physics-based models suggest dark energy may be evolving
Dark energy—the term used to describe whatever is causing the universe to expand at an increasing rate—is one of the universe’s greatest mysteries. The widely accepted theory at the present moment suggests that dark energy is constant, with the energy of empty space driving cosmic acceleration. However, last year, findings from the Dark Energy Survey (DES) and Dark Energy Spectroscopic Instrument (DESI) sparked excitement within the cosmology community by hinting that dark energy may actually be evolving. “This would be our first indication that dark energy is not the cosmological constant introduced by Einstein over 100 years ago but a new, dynamical phenomenon,” said Josh Frieman, Professor Emeritus of Astronomy and Astrophysics.
A new paper published in Physical Review D in September, by Frieman and Anowar Shajib, a NASA Hubble Fellowship Program Einstein Fellow in Astronomy and Astrophysics, combines current data from a multitude of probes, finding that dynamical models of evolving dark energy can better explain the data than the cosmological constant.
Shajib’s primary research focuses on observational cosmology and galaxy evolution, using strong gravitational lensing to measure the Hubble constant and constrain dark energy parameters. Frieman’s observational cosmology research leverages large cosmic surveys such as the Sloan Digital Sky Survey (SDSS) and the DES, with a particular emphasis on exploring the origin and evolution of the universe as well as understanding the nature of dark energy.
We spoke with Shajib and Frieman about the new models described in their paper, the implications of these results, and what’s next.
Why is dark energy significant in the study of the universe?
Frieman: We now know precisely how much dark energy there is in the universe, but we have no physical understanding of what it is. The simplest hypothesis is that it is the energy of empty space itself, in which case it would be unchanging in time, a notion that goes back to Einstein, Lemaitre, de Sitter, and others in the early part of the last century. It’s a bit embarrassing that we have little to no clue what 70 percent of the universe is. And whatever it is, it will determine the future evolution of the universe.
What recent findings led cosmologists to consider that dark energy may be evolving?
Shajib: Although there has been interest in the dynamical nature of dark energy since its discovery in the ’90s to resolve some observational discrepancies, until recently, most of the major and robust datasets were consistent with a non-evolving dark energy model, which is accepted as the standard cosmology. However, interest in evolving dark energy was vigorously rekindled last year from the combination of supernovae, baryon acoustic oscillation, and cosmic microwave background data from the DES, DESI, and Planck experiments. This combination of datasets indicated a strong discrepancy with the standard, non-evolving model of dark energy. The interesting feature of non-evolving dark energy is that its density stays constant through time even though space is expanding. However, for the evolving dark energy model, dark energy density will change with time.
Frieman: The data from these surveys allow us to infer the history of cosmic expansion—how fast the universe has been expanding at different epochs in the past. If dark energy evolves in time, that history will be different than if dark energy is constant. The cosmic expansion history results suggest that over the last several billion years or so, the density of dark energy has decreased by about 10 percent—not much, and much less than the densities of other matter and energy, but still significant.
What was the goal of this study, and what were the overall findings?
Shajib and Frieman: The goal of this study is to compare the predictions of a physical model for evolving dark energy with the latest data sets and to infer the physical properties of dark energy from this comparison. The evolving dark energy “model” used in most previous data analyses is just a mathematical formula that isn’t constrained to behave as physical models do. In our paper, we directly compare physics-based models for evolving dark energy to the data and find that these models describe the current data better than the standard, non-evolving dark energy model. We also show that near-future surveys such as DESI and the Vera Rubin Observatory Legacy Survey of Space and Time (LSST) will be able to definitively tell us whether these models are correct or if, instead, dark energy really is constant.
Describe the models presented and why they better explain the behavior of dark energy compared to existing models.
Frieman: These models are based on particle physics theories of hypothetical particles called axions. Axions were first predicted by physicists in the 1970s, who sought to explain certain observed features of strong interactions. Today, axions are considered plausible candidates for dark matter, and experiments worldwide are actively searching for them, including physicists at Fermilab and the University of Chicago.
The models in our paper are based on a different, ultra-light version of the axion that would act as dark energy, not dark matter. In these models, dark energy would, in fact, be constant for the first several billion years of cosmic history, but the axion would then start to evolve—like a ball on a sloping field that’s released from rest and starts to roll—and its density would slowly decrease, which is what the data appear to prefer. So the data suggest the existence of a new particle in nature that’s about 38 orders of magnitude lighter than the electron.
What are the implications of these findings for understanding cosmic expansion?
Shajib: In these models, the dark energy density decreases with time. Dark energy is the reason for the universe’s accelerated expansion, so if its density decreases, the acceleration will also decrease with time. If we consider the very far future of the universe, different characteristics of dark energy can lead to different outcomes. Two extremes of these outcomes are a Big Rip, where the accelerated expansion itself accelerates to the point that it rips everything apart, even atoms, and a Big Crunch, where the universe stops expanding at some point and recollapses, which will look like a reverse Big Bang. Our models suggest that the universe will avoid both of these extremes: it will undergo accelerated expansion for many billions of years, yielding a cold, dark universe—a Big Freeze.
Could these results have other, less apparent implications?
Frieman: The only practical implications I can imagine are the technologies we need to develop to explore these ideas further—building new telescopes, launching new satellites, or developing novel detectors, for example. Such developments are likely to have much more of an impact on our lives than events happening trillions of years in the future.
What excites you the most about these results?
Shajib: For this paper, we gathered all the major data sets—from the DES, DESI, SDSS, Time-Delay COSMOgraphy, Planck, and Atacama Cosmology Telescope—and combined them to get the most constraining measurement of dark energy to date. All these measurements come from extensive experiments, so in a way, they represent the collective knowledge that the cosmological community has gathered as a whole.
Frieman: When we began working on the DES in 2003, our goal was to constrain the properties of dark energy to determine whether it was constant or changing. For two decades, the data indicated that it was constant. We almost gave up on that question because the data consistently supported the assumption. However, we now have the first hint in over 20 years that dark energy might be changing, and if it is evolving, it must be something new, which would change our understanding of fundamental physics. That feeling is reminiscent of where we were at the beginning. It could still turn out that these hints are incorrect, but we may be on the cusp of answering that question, and that’s quite exciting.
Citation: “Scalar field dark energy models: Current and forecast constraints.” Anowar J. Shajib and Joshua A. Frieman, Phys. Rev. D 112, 063508.
Fly through Gaia’s 3D map of stellar nurseries
European Space Agency
image:
On this artist impression of the Milky Way, based on data from the European Space Agency’s Gaia telescope, the location of the new star-formation map is shown.
The star-formation region that is mapped out (contoured by a circle) reaches out to 4000 light-years from our Sun. The Sun is located at the centre of this region.
view moreCredit: ESA/Gaia/DPAC, S. Payne-Wardenaar, L. McCallum et al (2025)
Scientists created the most accurate three-dimensional map of star-formation regions in our Milky Way galaxy, based on data from the European Space Agency’s Gaia space telescope. This map will teach us more about these obscure cloudy areas, and the hot young stars that shape them.
It is notoriously difficult to map and study regions in space where stars form because they are usually hidden from view by thick clouds of gas and dust, whose distances cannot be directly measured.
Gaia can’t see these clouds directly, but it can measure stellar positions and the so-called ‘extinction’ of stars. This means it can see how much light from stars is blocked by dust. From this, scientists can create 3D maps showing where the dust is, and use those maps to figure out how much ionised hydrogen gas is present – a telltale sign of star formation.
Extremely bright, young stars
The new 3D map of star-forming regions in the Milky Way is based on Gaia observations of 44 million ‘ordinary’ stars and 87 O-type stars. The map extends to a distance of 4000 light-years from us, with the Sun at the centre.
O stars are rare stars: they are young, massive, and extremely bright and hot. They shine bright in ultraviolet light. These light rays are so energetic that they can strip electrons away from hydrogen atoms when hitting them. In this way, they ‘ionise’ the hydrogen gas around the hot stars, meaning it becomes a mixture of charged particles [1]. This is one way that astronomers can identify regions in space where stars are being born.
Many telescopes have observed these regions, so we have a good idea of what they look like from our point of view. But no one really knew what they look like in three dimensions, or from an outside perspective.
The Milky Way from above
Imagine that you are looking at the Milky Way from another galaxy. No spacecraft can travel beyond our galaxy, so we can’t take an actual photo. Fortunately, the Gaia mission is creating the most accurate multi-dimensional map of the Milky Way, giving astronomers the data to infer what it would look like.
Gaia’s sky maps – in all three spatial coordinates (3D) plus three velocities (moving towards and away from us, and across the sky) – have revealed the precise motions and positions of millions of nearby stars. With this, the telescope has already revolutionised our view of the solar neighbourhood, allowing scientists to comprehensively map the stars and interstellar material near the Sun in a way they were unable to do before.
“Gaia provides the first accurate view of what our section of the Milky Way would look like from above,” explains Lewis McCallum, astronomer at the University of St Andrews, UK, and first author of two scientific papers explaining the new 3D model.
“There has never been a model of the distribution of the ionised gas in the local Milky Way that matches other telescope’s observations of the sky so well. That’s why we are confident that our top-down view and fly-through movies are a good approximation of what these clouds would look like in 3D.”
Lewis’s new map includes 3D views of the Gum Nebula, the North American Nebula, the California Nebula, and the Orion-Eridanus superbubble. It allows us to fly around, through, and above these areas containing stellar nurseries.
Giant cavity of interstellar matter
With the map, scientists can learn more about how the giant O stars energise gas in our galaxy, and how far out their influence reaches. Lewis and his colleagues already noticed that some of the clouds in the star-forming regions seem to have broken open, and streams of gas and dust are likely venting into a giant cavity.
“This map nicely shows how radiation of massive stars ionises the surrounding interstellar medium and how dust and gas interact with this radiation. The 3D model provides a detailed look at the processes that shape our local galactic environment and helps astronomers understand interactions between the warm and cold components of the local Universe," explained Sasha Zeegers, ESA Research Fellow and an expert on interstellar dust.
In the future, this map will span an even larger area of the Milky Way. “It required huge computational power to generate the map out to ‘just’ 4000 light-years from the Sun in high resolution [2]. We hope that the map can be expanded further out once Gaia has released its new set of data,” says Lewis.
“Gaia’s distance measurements of the nearby hot stars, and the 3D maps of dust – obtained from measuring the extinction and positions of millions of ordinary stars using Gaia data – are both crucial ingredients of this new map. Gaia’s fourth data release will contain data of even better quality and quantity, making it possible to further advance our knowledge of star-forming regions,” confirms Johannes Sahlmann, ESA’s Gaia Project Scientist.
Scientists created the most accurate 3D map of star-formation regions in our Milky Way galaxy, based on data from the European Space Agency’s Gaia space telescope.
The star-formation region that is mapped out (contoured by a circle) reaches out to 4000 light-years from our Sun. The Sun is located at the centre of this region.
This is a still image of the animation showing Gaia’s star-formation map in 3D.
In this animation we fly around the star-formation map in our Milky Way galaxy. The areas that are mapped reach out to 4000 light-years from our Sun. They are shown as reddish clouds.
This map will teach us more about these obscure cloudy areas, and the hot young stars that shape them.
This is a still image of the animation showing Gaia’s star-formation map in 3D.
In this animation we fly around the star-formation map in our Milky Way galaxy. The areas that are mapped reach out to 4000 light-years from our Sun. They are shown as reddish clouds.
This map will teach us more about these obscure cloudy areas, and the hot young stars that shape them.
Fly through Gaia’s 3D map of stellar nurseries [VIDEO]
Scientists created the most accurate 3D map of star-formation regions in our Milky Way galaxy, based on data from the European Space Agency’s Gaia space telescope.
The star-formation region that is mapped out (contoured by a circle) reaches out to 4000 light-years from our Sun. The Sun is located at the centre of this region.
The star-formation map is plotted on an artist impression of our Milky Way, based on Gaia data.
Scientists created the most accurate 3D map of star-formation regions in our Milky Way galaxy, based on data from the European Space Agency’s Gaia space telescope.
This map will teach us more about these obscure cloudy areas, and the hot young stars that shape them.
In this animation we fly around the star-formation map in our Milky Way galaxy. The areas that are mapped reach out to 4000 light-years from our Sun. They are shown as reddish clouds.
Credit
ESA/Gaia/DPAC, S. Payne-Wardenaar, L. McCallum et al (2025)
Notes for editors
[1] Such an ionised hydrogen cloud is called a HII region by astronomers. A characteristic signal that can be picked up from these regions is the ‘hydrogen-alpha’ or ‘H-alpha’ spectral line at a wavelength of 656.3 nm.
[2] The work from Lewis McCallum and his team is based on earlier work published by Edenhofer et al in 2024, who created a dust map of our local galaxy. The new map presented today includes this previous map, and combined it with the hot (O) stars to visualise the ionised (star-forming) regions.
Two scientific papers by L. McCallum et al are published in Monthly Notices of the Royal Astronomical Society. https://academic.oup.com/mnrasl/article/540/1/L21/8085153 https://academic.oup.com/mnras/article/541/3/2324/8172009
Contact:
ESA Media relations
media@esa.int
Journal
Monthly Notices of the Royal Astronomical Society
ByDr. Tim Sandle
SCIENCE EDITOR
September 15, 2025
A lichen that grows like powder dusted on a rock.
NASA’s next phase of space exploration includes a human settlement on Mars. The costs and logistics are immense. One area where costs can be reduced is with construction. Instead of transporting all the construction materials from Earth to the red planet, using Martian soil to construct a site on Mars is seen by many scientists as the optimal approach.
Primarily, this involves finding a means to produce sulphur concrete, a material of a potential strength to be similar or higher levels of conventional Earth-based cementitious concrete.
Synthetic lichen system
A new self-growing technology carries the ability to assist future colonists with Martian architecture by using living biomaterials to 3D print structures. This is based on a new synthetic lichen system which uses fungi and bacteria to grow building materials directly from Martian soil. Moreover, this could occur autonomously and without human intervention.
Natural lichen is composed of algae or cyanobacteria living symbiotically with fungi. Lichens have properties different from those of their component organisms. They come in many colours, sizes, and forms and are sometimes plant-like, but are not plants.
The technology is being researched at Texas A&M University and the University of Nebraska-Lincoln. Here researchers have used bio-manufacturing engineered living materials as part of the NASA Innovative Advanced Concepts programme. The basis of the technology is to exploit the planet’s regolith (loose, fragmented surface material such as dust, sand and rocks). This is to provide the technological basis to build in the most demanding environments with restricted resources.
A variety of methods for bonding Martian regolith particles have previously been applied, including magnesium-based, sulphur-based, and a geopolymer creations. However, all such methods require significant human assistance and are generally regarded as unfeasible due to the expected lack of human resources on Mars.
This has led other research approaches to consider microbe-mediated self-growing technology. Various designs have been developed, such as bacterial biomineralization to bind sand particles into masonry, ureolytic bacteria to promote the production of calcium carbonate to make bricks, and an exploration of the use of fungal mycelium as a bonding agent.
While this microbe-mediated self-growing technology is very promising, the current practices are not completely autonomous since the microbes being used are limited to a single species or strain. This means that their survivability requires a continuous supply of nutrients, meaning outside intervention is needed.
The Texas A&M approach uses a synthetic community, making use of the advantages of multiple species. This system eliminates the need for external nutrient supplies. This design uses heterotrophic filamentous fungi as bonding material producers. The organisms can promote large amounts of biominerals as well as being able to survive harsh conditions. These fungi are paired with photoautotrophic diazotrophic cyanobacteria to create a synthetic lichen system.
Sulphur-based concrete
The diazotrophic cyanobacteria fix carbon dioxide and dinitrogen from the atmosphere and convert them into oxygen and organic nutrients to help the survival and growth of filamentous fungi as well as increasing the concentration of carbonate ions by photosynthetic activities.
The filamentous fungi bind metal ions onto fungal cell walls and serve as nucleation sites for biomineral production, as well as enhance the growth of cyanobacteria by providing them water, minerals, and carbon dioxide. Both components secrete biopolymers that enhance the adhesion and cohesion among Martian regolith and precipitated particles to create a consolidated body. Because the system grows with only Martian regolith simulant, air, light and an inorganic liquid medium, no human intervention is required.
Mycelial materials are currently commercially produced, known for creating insulators and fire retardant.
Studies have shown how these coculture systems display robust growth solely based on Martian regolith simulants, air, light, and an inorganic liquid medium without any additional carbon or nitrogen sources.
The research appears in the Journal of Manufacturing Science and Engineering, with the research paper titled “Bio-Manufacturing of Engineered Living Materials for Martian Construction: Design of the Synthetic Community.”
The ATREIDES program in search of lost exo-Neptunes
A team of astronomers led by UNIGE is launching a major research program on Neptunes to better understand the mechanisms of formation and evolution of planetary systems.
An international team led by the University of Geneva (UNIGE), including scientists from the National Centre of Competence in Research PlanetS, the University of Warwick, and the Canary Islands Institute of Astrophysics, has launched an ambitious program to map exoplanets located around the Neptunian Desert. The goal: to better understand the formation and evolution of planetary systems. This collaboration, known as ATREIDES, has delivered its first results with the observation of the TOI-421 planetary system. Analysis of this system reveals a surprisingly inclined orbital architecture, offering new insights into the chaotic history of these distant worlds. This inaugural study has been published in the journal Astronomy & Astrophysics.
What are the physical mechanisms that govern the formation and evolution of planetary systems? To address this broad question, a group of scientists led by the UNIGE Department of Astronomy decided to focus on a specific class of exoplanets: exo-Neptunes, planets outside our solar system that are about 20 times more massive than Earth.
Over the past decade, scientists have made major discoveries about the distribution of exoplanets. Exo-Neptunes are absent in regions very close to stars. However, recent studies, in which UNIGE has participated, show that in areas slightly farther away from stars—a more temperate region in the distribution of exoplanets known as the “savanna” — this type of planet is more prevalent. Finally, between this savanna and the desert lies a region called the “Neptunian ridge,” where exo-Neptunes are even more numerous than in the other two regions.
‘‘The complexity of the exo-Neptunian landscape provides offers a unique window onto the processes involved in the formation and evolution of planetary systems. This is what inspired the ambitious ATREIDES scientific cooperation, which is based in particular on a large-scale observation program that we are conducting on the largest European telescopes — the ESO’s VLTs — using the world’s most accurate spectrograph, ESPRESSO,’’ explains Vincent Bourrier, senior lecturer and researcher in the Department of Astronomy at the UNIGE Faculty of Science, principal investigator of the ATREIDES program, and lead author of the consortium’s first study.
Conquering the “desert”
The ATREIDES program focuses on exo-Neptunes to identify the processes responsible for Neptunian ridge, savanna, and desert, and to derive more general information about the formation and evolution of planets. Scientists plan to use ESPRESSO to observe a large number of Neptunes and to analyse and model data from all planets in a consistent and coherent framework. This systematic approach should enable a real comparison between different planetary systems and a better understanding of the mechanisms that shape this complex Neptunian landscape.
Designed as an open, international community initiative, the ATREIDES collaboration invites all interested astronomers to join this scientific effort, following the example of the University of Warwick. «We are using the NGTS telescopes, an exoplanet observation program based on the transit method, to observe the transits of these Neptunes and thus optimise our use of ESPRESSO/VLT. This allows us to obtain much more accurate measurements and identify processes, such as stellar flares, that could affect the ESPRESSO data,» says Daniel Bayliss, associate professor in the Department of Physics at the University of Warwick.
TOI-421: a “misaligned” orbital architecture
The first system observed and analysed as part of ATREIDES is called TOI-421. It has two planets: a hot Neptune, TOI-421 c, located in the savanna, and a smaller planet closer to the star, TOI-421 b. Astronomers have been able to trace the chaotic history of this system.
One of the hypotheses of the ATREIDES program states that the Neptunian landscape was sculpted by the way these planets migrated from their birthplace to their current orbits. Some planets would migrate slowly and early through the gas disk in which they formed, a process that should produce aligned orbits. Others would be violently propelled into their orbits much later, through a chaotic process called “high-eccentricity migration,” which results in highly misaligned orbits.
One of the key variables in this hypothesis is therefore the alignment between the star’s equatorial plane and the orbital plane of each planet. By measuring this alignment for TOI-421, scientists were able to show that the two planets in the system are highly misaligned, which is very different from our solar system where the planets are aligned and therefore rotate almost in the equatorial plane of our Sun. This points to a turbulent history in the evolution of the TOI-421 system after its formation.
The analysis of TOI-421 is just a taste of what is to come. It provides valuable information to scientists but also, and above all, helps to refine the analysis and modeling tools developed in the ATREIDES collaboration. However, a large number of planetary systems with exo-Neptunes will need to be observed and analyzed with the same rigor before we can outline the evolution and formation of planetary systems.
“A thorough understanding of the mechanisms that shape the Neptunian desert, savanna, and ridge will provide a better understanding of planetary formation as a whole...but it’s a safe bet that the Universe has other surprises in store for us, which will force us to develop new theories,” concludes Vincent Bourrier.
Journal
Astronomy and Astrophysics
Method of Research
News article
Subject of Research
Not applicable
Article Title
Embarking on a trek across the exo-Neptunian landscape with the TOI-421 system
Article Publication Date
16-Sep-2025
UT San Antonio astronomy professor awarded for advancements in planetary science
Xinting Yu, assistant professor in the Department of Physics and Astronomy at The University of Texas at San Antonio, is one of two recipients of the 2025 Harold C. Urey Prize.
Xinting Yu, assistant professor in the Department of Physics and Astronomy at The University of Texas at San Antonio, is one of two recipients of the 2025 Harold C. Urey Prize.
The national award from the American Astronomical Society’s Division for Planetary Sciences recognizes early-career scientists shaping the future of space research.
Yu was honored for her research in planetary and exoplanetary science — the study of planets in our solar system and beyond. Her work focuses on how planetary surfaces and atmospheres interact and evolve.
By combining lab experiments with computer modeling, Yu is helping scientists better understand phenomena ranging from windblown dunes on Saturn’s moon Titan to the thick clouds enveloping distant exoplanets.
Yu’s lab studies unusual planetary materials, like icy particles and haze, to understand their behavior in extreme environments. Her team has published more than 15 papers in top journals and been featured in national science media.
Mini-Neptunes
One of her most memorable research discoveries happened in 2021, Yu said, when she predicted atmospheric compositions of exoplanets measurable by the James Webb Space Telescope (JWST) could help scientists distinguish “mini-Neptunes” from “super-Earths.” The intermediate-sized planets, the most abundantly discovered so far, don’t exist in our solar system and little is known about them.
“It’s really important to know whether some of these planets could have surface conditions like Earth so we can expand our search for habitable worlds beyond Earth-sized planets,” Yu said.
The space telescope can’t directly observe the planets’ surfaces, so Yu’s method uses atmospheric data to probe them indirectly. Now that the telescope has begun collecting data, her approach is being applied in ongoing research to interpret observations of several exoplanets outside of our solar system that are the strongest candidates for harboring life.
As part of Yu’s research group, UTSA graduate student Cindy Luu recently published a 2024 study describing K2-18 b, a super-Earth exoplanet located outside of our solar system that is believed to be a sort of water world with a supercritical water ocean.
This work applied Yu’s atmospheric analysis methods to offer insights that could reshape how scientists view sub-Neptune worlds, further advancing the lab’s mission to understand distant exoplanets.
Magic islands
In 2024, Yu made headlines with her research on Titan’s mysterious “magic islands” — bright patches that appear and disappear in its methane seas. Her research suggests they are clumps of floating organic material, like icebergs, and proposes a thin frozen layer may coat Titan’s lakes, explaining their smooth appearance.
Currently, Yu is leading a project studying “missing” methane gases in warm-to-hot exoplanet atmospheres. Her team developed a fast, geochemistry-inspired framework suggesting these planets may have hotter interiors than models predict, showing how atmospheric chemistry probes planetary interiors.
The professor is also developing ways to determine if distant planets have solid or liquid surfaces using atmospheric data, inspired by Titan and Jupiter’s contrasting atmospheres. This could help identify potentially habitable worlds using JWST data.
How planets form
Yu’s research team is expanding into planet formation research and aims to use her lab’s Planetary Material Characterization Facility (PMCHEF) to study early solar system materials. Besides analyzing carbon-rich meteorite samples they already possess, the team hopes to study samples from asteroid Bennu and a future NASA comet sample-return mission.
“This would help us address multiple open questions in the field, such as how elements go into forming planets and how planets form from very tiny dust particles,” Yu said.
Before joining the university in 2023, Yu was a postdoctoral fellow at the University of California, Santa Cruz through the 51 Pegasi b Fellowship.
In her first year at UT San Antonio, she launched the Texas Area Planetary Science (TAPS) Meeting to foster local collaboration among planetary and exoplanet scientists. In 2023, she also received NASA’s Planetary Science Early Career Award, which helped establish her lab, PMCHEF.
With her research and leadership, Yu is helping UTSA grow its planetary science discovery effort and expand understanding of worlds near and far.
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