SPACE/COSMOS
Solar rain mystery cracked by researchers
University of Hawaii at Manoa
image:
Researchers worked for years to unlock the mystery of solar rain in solar flares.
view moreCredit: NASA/Goddard/SDO
It rains on the Sun, and thanks to researchers at the University of Hawaiʻi Institute for Astronomy (IfA), we finally know why.
Unlike water that falls from the sky on Earth, solar rain happens in the Sun’s corona, a region of super-hot plasma above its surface. This rain consists of cooler, denser blobs of plasma that fall back down after forming high in the coronae. For decades, scientists struggled to explain how this rain forms so quickly during solar flares.
New explanation
That mystery was cracked by Luke Benavitz, a first-year graduate student at IfA, and IfA astronomer Jeffrey Reep. Their work, recently published in the Astrophysical Journal, adds a missing piece to decades of solar models.
“At present, models assume that the distribution of various elements in the corona is constant throughout space and time, which clearly isn’t the case,” said Benavitz. “It’s exciting to see that when we allow elements like iron to change with time, the models finally match what we actually observe on the Sun. It makes the physics come alive in a way that feels real.”
Why it matters
The new finding means solar scientists can better model how the Sun behaves during flares, insights that could one day help predict space weather that affects our daily lives.
Earlier models required heating over hours or days to explain coronal rain; however, solar flares can happen in just minutes. The IfA team’s work shows that shifting elemental abundances can explain how rain can quickly form.
“This discovery matters because it helps us understand how the Sun really works,” said Reep. “We can’t directly see the heating process, so we use cooling as a proxy. But if our models haven’t treated abundances properly, the cooling time has likely been overestimated. We might need to go back to the drawing board on coronal heating, so there’s a lot of new and exciting work to be done.”
Fresh insights
This research opens the door to a much wider range of questions. Scientists now know that elemental abundances in the Sun’s atmosphere should change over time, which challenges long-standing models that assumed they were fixed. This means the discovery reaches far beyond coronal rain, pushing researchers to rethink how the Sun’s outer layers behave and how energy moves through its atmosphere.
Bright solar eruption captured in space.
Credit
NASA/Solar Dynamics Observatory
Journal
The Astrophysical Journal
Dark matter and dark energy may only be a cosmic illusion
University of Ottawa
image:
“With our model, you don’t need to assume any exotic particles or break the rules of physics”
Rajendra Gupta
— Adjunct Professor in the Department of physics at the University of Ottawa
view moreCredit: University of Ottawa
For decades, astronomers have believed that dark matter and dark energy make up most of the universe, however, a new study suggests they might not exist at all. Instead, what we perceive as dark matter and dark energy could simply be the effect of the natural forces of the universe slowly weakening as it ages.
Led by Rajendra Gupta, Adjunct Professor in the Department of physics at the University of Ottawa, the study asserts that if the basic strengths of nature’s forces (like gravity) slowly change over time and in space, they can explain the strange phenomena we observe, such as the way galaxies evolve and spin and how the universe expands.
Challenging established concepts
“The universe’s forces actually get weaker on the average as it expands,” Professor Gupta explains. “This weakening makes it look like there’s a mysterious push making the universe expand faster (which is identified as dark energy). However, at galactic and galaxy-cluster scale, the variation of these forces over their gravitationally bound space results in extra gravity (which is considered due to dark matter). But those things might just be illusions, emergent from the evolving constants defining the strength of the forces.”
He adds, “There are two very different phenomena needed to be explained by dark matter and dark energy: The first is at cosmological scale, that is, at a scale larger than 600 million light years assuming the universe is homogeneous and the same in all directions. The second is at astrophysical scale, that is, at smaller scale the universe is very lumpy and direction dependent. In the standard model, the two scenarios require different equations to explain observations using dark matter and dark energy. Ours is the only one that explains them with the same equation, and without needing dark matter or dark energy.”
He adds, “What’s really exciting is that this new approach lets us explain what we see in the sky: galaxy rotation, galaxy clustering, and even the way light bends around massive objects, without having to imagine there’s something hiding out there. It’s all just the result of the constants of nature varying as the universe ages and becomes lumpy.”
New model applied at Astrophysical Scale
Last year, Professor Gupta challenged the existence of dark matter in the universe in his cosmological-scale study. In this astrophysical-scale work, he questioned the current theoretical models for the galaxy rotation curves.
- In the new model, the parameter often denoted α emerges from allowing the coupling constants to evolve. In effect, α behaves like an extra “component” in the gravitational equations that produces effects similar to what astronomers attribute to dark matter and dark energy.
- On cosmological scales, α is treated as a constant (e.g., determined by fitting supernovae data). But locally (on astrophysical scale), in a galaxy, because the standard matter (black holes, stars, planets, gas, etc.) distribution varies drastically, α varies causing the extra gravitational effect to depend on where such matter is. So the new theory predicts that in regions where there’s a lot of standard matter, the extra gravity effect is less, and where detectable matter density is low, it is larger.
- In effect, instead of adding dark matter halos around galaxies, the extra gravitational pull comes from α in the new model. It reproduces the observed “flat rotation curves” (stars moving faster than expected in the outer parts of galaxies).
Implications for astronomy
Professor Gupta believes this idea could solve some of the biggest puzzles in astronomy. “For years, we’ve struggled to explain how galaxies in the early universe formed so quickly and became so massive,” he says. “With our model, you don’t need to assume any exotic particles or break the rules of physics. The timeline of the universe simply stretches out, almost doubling the universe’s age, and making room for everything we observe.”
Effectively, the stretched out timeline for how stars and galaxies form, makes it much easier to explain how big, complex structures like galaxies and black holes could have appeared so early in the universe.
This theory could completely change how we think about the universe. It even hints that searching for dark matter particles, something scientists have spent years and billions of dollars on, might not be necessary after all. Even if the exotic particles are experimentally found they would need to constitute about six times the mass of the standard matter.
“Sometimes, the simplest explanation is the best one. Maybe the universe’s biggest secrets are just tricks played by the evolving constants of nature,” Professor Gupta concludes.
The study, titled “Testing CCC+TL Cosmology with Galaxy Rotation Curves”, was published in the peer-reviewed journal Galaxies.
Journal
Galaxies
Method of Research
Data/statistical analysis
Subject of Research
Not applicable
Article Title
Testing CCC+TL Cosmology with Galaxy Rotation Curves
Potential smoking gun signature of supermassive dark stars found in JWST data
image:
This image taken by the James Webb Space Telescope highlights the region of study by the JWST Advanced Deep Extragalactic Survey (JADES). This area is in and around the Hubble Space Telescope’s Ultra Deep Field.
view moreCredit: NASA
The first stars in the universe formed out of pristine hydrogen and helium clouds, in the first few hundred million years after the Big Bang. New James Webb Space Telescope (JWST) observations reveal that some of the first stars in the universe could have been very different from regular (nuclear fusion-powered) stars, which have been observed and catalogued by astronomers for millennia. A recent study led by Cosmin Ilie, at Colgate University, in collaboration with Shafaat Mahmud (Colgate ’26), Jillian Paulin (Colgate ’23) at UPenn, and Katherine Freese, at The University of Texas at Austin, identifies four extremely distant objects which are consistent, both from the point of view of their observed spectra and morphology, with being supermassive dark stars.
“Supermassive dark stars are extremely bright, giant, yet puffy clouds made primarily out of hydrogen and helium, which are supported against gravitational collapse by the minute amounts of self-annihilating dark matter inside them,” Ilie said. Supermassive dark stars and their black hole remnants could be key to solving two recent astronomical puzzles: i. the larger than expected extremely bright, yet compact, very distant galaxies observed with JWST, and ii. the origin of the supermassive black holes powering the most distant quasars observed.
Freese developed the original theory behind dark stars with Doug Spolyar and Paolo Gondolo. They published their first peer-reviewed paper on this theory in the journal Physical Review Letters in 2008. In that paper, they envisioned how such dark stars might have led to supermassive black holes in the early universe. In a 2010 Astrophysical Journal publication, Freese, Ilie, Spolyar, and collaborators identified two mechanisms via which dark stars can grow to become supermassive, and predicted that they could seed the supermassive black holes powering many of the most distant quasars in the Universe.
Although dark matter makes up about 25% of the universe, its nature has eluded scientists. It is now widely believed that dark matter consists of a new type of elementary particle, yet to be observed or detected. While the hunt to detect such particles has been on for a few decades, no conclusive evidence has been found yet. Among the leading candidates for dark matter are Weakly Interacting Massive Particles. When they collide, these particles would theoretically annihilate themselves, depositing heat into collapsing clouds of hydrogen and converting them into brightly shining dark stars.
The conditions for the formation of dark stars were just right a few hundred million years after the Big Bang, and at the center of dark matter halos. This is when, and where the first stars in the universe are expected to have formed.
“For the first time we have identified spectroscopic supermassive dark star candidates in JWST, including the earliest objects at redshift 14, only 300 Myr after the Big Bang,” said Freese, the Jeff and Gail Kodosky Endowed Chair in Physics and director of the Weinberg Institute and Texas Center for Cosmology and Astroparticle Physics at UT Austin. “Weighing a million times as much as the Sun, such early dark stars are important not only in teaching us about dark matter but also as precursors to the early supermassive black holes seen in JWST that are otherwise so difficult to explain.”
In a 2023 PNAS study by Ilie, Paulin, and Freese, the first supermassive dark star candidates (JADES-GS-z13-0, JADES-GS-z12-0, and JADES-GS-z11-0) were identified using photometric data from JWST’s NIRCam instrument. Since then, spectra from JWST’s NIRSpec instrument became available for those, and a few other extremely distant objects. The team, which now also includes Shafaat Mahmud analyzed the spectra and morphology of four of the most distant objects ever observed (including two candidates from the 2023 study): JADES-GS-z14-0, JADES-GS-z14-1, JADES-GS-13-0, and JADES-GS-z11-0 and found that each of them is consistent with a supermassive dark star interpretation.
JADES-GS-z14-1 is not resolved, meaning it is consistent with a point source, such as a very distant supermassive star would be. The other three are extremely compact, and can be modeled by supermassive dark stars powering a nebula (i.e. ionized H and He gas surrounding the star). Each of the four objects analyzed in this study is also consistent with a galaxy interpretation, as shown in the literature. Dark stars have a smoking gun signature, an absorption feature at 1640 Angstrom, due to the large amounts of singly ionized helium in their atmospheres. And in fact, one of the four objects analyzed shows signs of this feature.
“One of the most exciting moments during this research was when we found the 1640 Angstrom absorption dip in the spectrum of JADES-GS-z14-0. While the signal to noise ratio of this feature is relatively low (S/N~2), it is for the first time we found a potential smoking gun signature of a dark star. Which, in itself, is remarkable,” Ilie said.
Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) measured the spectrum of the same object, revealing the presence of oxygen, via a nebular emission line. Researchers said that if both spectral features are confirmed, the object cannot be an isolated dark star, but rather may be a dark star embedded in a metal rich environment. This could be the outcome of a merger, where a dark matter halo hosting a dark star merges with a galaxy. Alternatively, dark stars and regular stars could have formed in the same host halo, as the researchers now realized it is possible.
The identification of supermassive dark stars would open up the possibility of learning about the dark matter particle based on the observed properties of those objects, and would establish a new field of astronomy: the study of dark matter-powered stars. This published PNAS research is a key step in this direction.
Funding Acknowledgements: This research was made possible by generous funding from the following agencies: Colgate University Research Council, The Picker Interdisciplinary Sciences Institute, the U.S. Department of Energy’s Office of High Energy Physics program, Swedish Research Council, LSST Discovery Alliance, the Brinson Foundation, the WoodNext Foundation, and the Research Corporation for Science Advancement Foundation.
Journal
Proceedings of the National Academy of Sciences
Method of Research
Observational study
Subject of Research
Not applicable
Article Title
Spectroscopic Supermassive Dark Star candidates
Article Publication Date
29-Sep-2025
Cassini proves complex chemistry in Enceladus ocean
European Space Agency
image:
Cassini image looking across the south pole of Saturn's icy moon Enceladus on 30 November 2010. Jets of water from the moon's underground ocean are visible bursting through cracks in the ice.
view moreCredit: NASA/JPL-Caltech/Space Science Institute
Scientists digging through data collected by the Cassini spacecraft have found new complex organic molecules spewing from Saturn’s moon Enceladus. This is a clear sign that complex chemical reactions are taking place within its underground ocean. Some of these reactions could be part of chains that lead to even more complex, potentially biologically relevant molecules.
Published today in Nature Astronomy, this discovery further strengthens the case for a dedicated European Space Agency (ESA) mission to orbit and land on Enceladus.
In 2005, Cassini found the first evidence that Enceladus has a hidden ocean beneath its icy surface. Jets of water burst from cracks close to the moon’s south pole, shooting ice grains into space. Smaller than grains of sand, some of the tiny pieces of ice fall back onto the moon’s surface, whilst others escape and form a ring around Saturn that traces Enceladus’s orbit.
Lead author Nozair Khawaja explains what we already knew: “Cassini was detecting samples from Enceladus all the time as it flew through Saturn’s E ring. We had already found many organic molecules in these ice grains, including precursors for amino acids.
The ice grains in the ring can be hundreds of years old. As they have aged, they may have been ‘weathered’ and therefore altered by intense space radiation. Scientists wanted to investigate fresh grains ejected much more recently to get a better idea of what exactly is going on in Enceladus’s ocean.
Fortunately, we already had the data. Back in 2008, Cassini flew straight through the icy spray. Pristine grains ejected only minutes before hit the spacecraft’s Cosmic Dust Analyzer (CDA) instrument at about 18 km/s. These were not only the freshest ice grains Cassini had ever detected, but also the fastest.
The speed mattered. Nozair explains why:
“The ice grains contain not just frozen water, but also other molecules, including organics. At lower impact speeds, the ice shatters, and the signal from clusters of water molecules can hide the signal from certain organic molecules. But when the ice grains hit CDA fast, water molecules don’t cluster, and we have a chance to see these previously hidden signals.”
It took years to build up knowledge from previous flybys and then apply it to decipher this data. But now, Nozair’s team has revealed what kind of molecules were present inside the fresh ice grains.
They saw that certain organic molecules that had already been found distributed in the E ring were also present in the fresh ice grains. This confirms that they are created within Enceladus’s ocean.
They also found totally new molecules that had never been seen before in ice grains from Enceladus. For the chemists reading, the newly detected molecular fragments included aliphatic, (hetero)cyclic ester/alkenes, ethers/ethyl and, tentatively, nitrogen- and oxygen-bearing compounds.
On Earth, these same molecules are involved in the chains of chemical reactions that ultimately lead to the more complex molecules that are essential for life.
“There are many possible pathways from the organic molecules we found in the Cassini data to potentially biologically relevant compounds, which enhances the likelihood that the moon is habitable,” says Nozair.
“There is much more in the data that we are currently exploring, so we are looking forward to finding out more in the near future.”
Co-author Frank Postberg adds: “These molecules we found in the freshly ejected material prove that the complex organic molecules Cassini detected in Saturn’s E ring are not just a product of long exposure to space, but are readily available in Enceladus’s ocean.”
Nicolas Altobelli, ESA Cassini project scientist adds: “It’s fantastic to see new discoveries emerging from Cassini data almost two decades after it was collected. It really showcases the long-term impact of our space missions. I look forward to comparing data from Cassini with data from ESA’s other missions to visit the icy moons of Saturn and Jupiter.”
Returning to Enceladus
Discoveries from Cassini are valuable for planning a future ESA mission dedicated to Enceladus. Studies for this ambitious mission have already begun. The plan is to fly through the jets and even land on the moon's south polar terrain to collect samples.
A team of scientists and engineers is already considering the selection of modern scientific instruments that the spacecraft would carry. This latest result made using CDA will help guide that decision.
Enceladus ticks all the boxes to be a habitable environment that could support life: the presence of liquid water, a source of energy, a specific set of chemical elements and complex organic molecules. A mission that takes measurements directly from the moon’s surface, seeking out signs of life, would offer Europe a front seat in Solar System science.
“Even not finding life on Enceladus would be a huge discovery, because it raises serious questions about why life is not present in such an environment when the right conditions are there,” says Nozair.
The process of light, soluble and reactive organic molecules making their way onto ice grains emitted in jets of water from Saturn's moon Enceladus, where they were detected by the Cassini spacecraft.
Credit
NASA/JPL-Caltech
How we think hydrothermal activity works on Enceladus, based on data from the NASA/ESA Cassini-Huygens mission
Credit
ESA
This artist’s impression depicts thermal jets venting through the icy surface at the southern polar region of Saturn’s moon Enceladus.
Credit
ESA/Science Office
Notes for editors
‘Detection of Organic Compounds in Freshly Ejected Ice Grains from Enceladus’s Ocean’ by N. Khawaja et al. is published today in Nature Astronomy. DOI: 10.1038/s41550-025-02655-y
Lead author Nozair Khawaja conducted the research at Freie Universität Berlin and the University of Stuttgart, both in Germany. Frank Postberg is also affiliated with Freie Universität Berlin.
Cassini-Huygens was a cooperative project of NASA, ESA and the Italian Space Agency. It comprised two elements: the Cassini orbiter and the Huygens probe.
Cassini’s Cosmic Dust Analyzer (CDA) was led by the University of Stuttgart in Germany.
For more information please contact:
Journal
Nature Astronomy
Method of Research
Observational study
Subject of Research
Not applicable
Article Title
Detection of Organic Compounds in Freshly Ejected Ice Grains from Enceladus’s Ocean
Article Publication Date
1-Oct-2025
Patchwork planets: Piecing together the early solar system
New Haven, Conn. — Our solar system is a smashing success.
A new study suggests that from its earliest period — even before the last of its nebular gas had been consumed — Earth’s solar system and its planets looked more like a bin of well-used LEGO blocks than slowly-evolving spheres of untouched elements and minerals.
“Far from being made of pristine material, planets — including Earth — were built from recycled fragments of shattered and rebuilt bodies,” said Damanveer Singh Grewal, an assistant professor of Earth and planetary science in Yale’s Faculty of Arts and Sciences and first author of a new study in the journal Science Advances. “Our research paints a clearer picture of the violent origins of our solar system.”
Scientists have long known that in the earliest days of the solar system, planets and protoplanets known as “planetesimals” formed via a combination of collisions and core formation, which triggered chemical changes to the cores’ composition. But the level of influence for each of these forces has been unknown. Adding to the mystery, some planetesimals have unusual chemical signatures that would require the presence of highly unlikely metals at the start of a naturally evolving core formation process.
Grewal and his colleagues say the explanation lies with the smash-and-rebuild nature of the early solar system.
For the new study, the researchers created simulations of how planetary cores developed in the early years of the solar system based on a reinterpretation of data taken from iron meteorites — the remnants of the metallic cores of the first planetesimals.
The researchers hypothesize that high-energy collisions began 1 million to 2 million years after the forming of the solar system (considered “early” in cosmological terms). At that stage, some planetesimals had formed metal-rich cores, but the process was not complete.
Collisions shattered these cores, and their fragments later reassembled themselves into new planetary bodies.
“These events determined which elements and minerals young worlds carried into the next stage of planet formation,” Grewal said. “Our findings show that the pathway to planetary formation was far more dynamic and complex than previously thought.”
Varun Manilal, a graduate student in Earth and planetary sciences at Yale, is co-author of the study. Additional co-authors are Zhongtian Zhang, a former Carnegie Institution of Science postdoctoral fellow who is now at Princeton, Thomas Kruijer of the Lawrence Livermore National Laboratory, William Bottke of Southwest Research Institute, and Sarah Stewart of Arizona State University.
Funding for the research came from Yale, Arizona State University, and Lawrence Livermore National Laboratory.
Journal
Science Advances
Article Title
Protracted Core Formation and Impact Disruptions Shaped the Earliest Outer Solar System Planetesimals
Article Publication Date
1-Oct-2025
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