astrophysics

This black hole “burps” with Death Star energy

astronomy, astrophysics, black holes, Science, tidal disruption events / Kelly Newman / February 5, 2026

When AT2018hyz, aka “Jetty,” was first discovered, radio telescopes didn’t detect any signatures of an outflow emission of material within the first few months. According to Cendes, that’s true of some 80 percent of TDEs, so astronomers moved on, preferring to use precious telescope time for more potentially interesting objects. A few years later, radio data from the Very Large Array (VLA) showed that Jetty was lighting up the skies again, spewing out material at a whopping 1.4 millijansky at 5 GHz.

Since then, that brightness has kept increasing. Just how large is the increase? Well, people have estimated the fictional Death Star’s emitted energy in the Star Wars saga, and Jetty McJetface’s emissions are a trillion times more than that, perhaps as much as 100 trillion times the energy. As for why Jetty initially eluded detection, there seems to be a single jet emitting radiation in one direction that might not have been aimed at Earth. Astronomers should be able to confirm this once the energy peaks.

Cendes and her team are now scouring the skies for similar behavior in high-energy TDEs, since the existence of Jetty suggests that delayed outflow is more common than astronomers previously expected. It’s such an unprecedented phenomenon that astronomers haven’t really looked for them before. After all, “If you have an explosion, why would you expect there to be something years after the explosion happened when you didn’t see something before?” said Cendes.

DOI: Astrophysical Journal, 2026. 10.3847/1538-4357/ae286d (About DOIs).

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NASA launches new mission to get the most out of the James Webb Space Telescope

astrophysics, exoplanets, goddard space flight center, launch, NASA, pandora, Science, Space, spacex / Mike M. / January 12, 2026

“It was not recognized how serious a problem that is until… about 2017 or 2018.”

The Pandora observatory, seen here inside a clean room, is about the size of a refrigerator. Credit: Blue Canyon Technologies

Among other things, the James Webb Space Telescope is designed to get us closer to finding habitable worlds around faraway stars. From its perch a million miles from Earth, Webb’s huge gold-coated mirror collects more light than any other telescope put into space.

The Webb telescope, launched in 2021 at a cost of more than $10 billion, has the sensitivity to peer into distant planetary systems and detect the telltale chemical fingerprints of molecules critical to or indicative of potential life, like water vapor, carbon dioxide, and methane. Webb can do this while also observing the oldest observable galaxies in the Universe and studying planets, moons, and smaller objects within our own Solar System.

Naturally, astronomers want to get the most out of their big-budget observatory. That’s where NASA’s Pandora mission comes in.

The Pandora satellite rocketed into orbit early Sunday from Vandenberg Space Force Base, California. It hitched a ride with around 40 other small payloads aboard a SpaceX Falcon 9 rocket, launching into a polar Sun-synchronous orbit before deploying at an altitude of roughly 380 miles (613 kilometers).

Over the next few weeks, ground controllers will put Pandora through a series of commissioning and calibration steps before turning its eyes toward deep space. Pandora is a fraction of the size of Webb. Its primary mirror is about the size of the largest consumer-grade amateur telescopes, less than one-tenth the dimension of Webb’s. NASA capped Pandora’s budget at $20 million. The budget to develop Webb was more than 500 times higher.

Double-checking Webb

So what can little Pandora add to Webb’s bleeding-edge science? First, it helps to understand how scientists use Webb to study exoplanets. When a planet passes in front of its parent star, some of the starlight shines through its atmosphere. Webb has the sensitivity to detect the filtered starlight and break it apart into its spectral components, telling astronomers about the composition of clouds and hazes in the planet’s atmosphere. Ultimately, the data is useful in determining whether an exoplanet might be like Earth.

“I liken it often to holding a glass of wine in front of a candle, so that we can see really what’s inside,” said Daniel Apai, a member of Pandora’s science team from the University of Arizona. “We can assess, basically, the quality of the wine. In this case, we use the light that filters through the star’s [atmosphere] through the planetary atmosphere to judge what chemicals, gases in particular, may be present. Water vapor is one that we are the most sensitive to.”

But there’s a catch. Stars shine millions to billions of times brighter than their planetary companions, and starlight isn’t constant. Like the Sun, other stars have spots, flares, and variability over hours, days, or years. Hot spots and cool spots rotate in and out of view. And the star’s own atmospheres can contain some of the same molecules scientists are seeking to find on exoplanets, including water vapor.

Therefore, a star’s spectral signature easily outshines the signal coming from a nearby planet. Astronomers discovered this signal “contamination” when they started looking for potentially habitable worlds, injecting confounding uncertainties into their findings. Were the promising spectra they were seeing coming from the planet or the star?

Artist’s concept of the Pandora telescope with an exoplanet and two stars in the background. Credit: NASA’s Goddard Space Flight Center/Conceptual Image Lab

“One of the ways that this manifests is by making you think that you’re seeing absorption features like water and potentially methane when there may not be any, or, conversely, you’re not seeing the signatures that are there because they’re masked by the stellar signal,” said Tom Barclay, deputy project scientist and technical lead on the Pandora mission at NASA’s Goddard Space Flight Center.

The problem became apparent in the 2010s as astronomers used more powerful telescopes to see the finer details of exoplanets.

“This is something that we always suspected as a community,” Apai told Ars. “We always suspected that stars are not perfect. At some point, it becomes a problem. But it was not recognized how serious a problem that is until, I would say, about 2017 or 2018.”

Scientists quickly got to work looking for a solution, and NASA selected the Pandora mission for development in 2021, just months before the launch of Webb.

“When we’re trying to find water in the atmospheres of these small Earth-like planets, we want to be really sure it’s not coming from the star before we go tell the press and make a big stink about it,” said Elisa Quintana, Pandora’s lead scientist at NASA’s Goddard Space Flight Center. “So we designed the Pandora mission specifically to solve this problem.”

From low-Earth orbit, Pandora will observe exoplanets and their stars simultaneously, allowing astronomers to correct their measurements of the planet’s atmospheric composition and structure based on the ever-changing conditions of the host star itself. Webb could theoretically do this work, but scientists already fill every hour of Webb’s schedule. Pandora will point and stare at 20 preselected exoplanets 10 times during its one-year prime mission, collecting 24 hours of visible and infrared observations with each visit. This will capture short-term and longer-term changes in each star’s behavior.

SpaceX launched Pandora into a so-called “twilight orbit” that follows the boundary between day and night on Earth, allowing the satellite to keep its solar panels illuminated by the Sun while performing its observations.

“We can send this small telescope out, sit on a star for a really long time, and sort of map all the star spots, and really disentangle the star and planet signals,” Quintana said in a recent panel discussion at NASA Goddard. “It’s filling a really nice gap in helping us to sort of calibrate all these stars that James Webb is going to look at, so we can be really confident that all of these molecules that we’re detecting in planets are real.”

“I think this is really the most important scientific barrier that we have to break down to fully unlock the potential of Webb and future missions,” Apai said.

Looking down the barrel of Pandora’s 17-inch-wide (45-centimeter) telescope. Credit: NASA/Jordan Karburn, LLNL

Ben Hord, a member of Pandora’s science team at Goddard, singled out one example in a presentation at an American Astronomical Society meeting last year. This planet, named GJ 486 b, is a “super-Earth” discovered in 2021 circling a relatively cool red dwarf star. Hord said astronomers had trouble determining if the planet has a water-rich atmosphere based on Webb’s observations alone.

“We want to know if water is in the atmospheres of these exoplanets, and this stellar contamination from the spots on the star can mask or mimic features like water,” Hord said. “Our hope is that Pandora will help James Webb data be even more precise by providing context and understanding for these host stars and these planetary systems.”

Planets around small dwarf stars are some of the best candidates for finding a true Earth analog. Because these stars put out a fraction of the heat of the Sun, a potentially habitable planet could lurk very close to its host, completing a year in a handful of days. This allows astronomers to see the planet repeatedly as it passes in front of its star, rapidly building a dataset on its size, structure, and environment.

Scientists hope they can extend the lessons learned from Pandora’s observations of a sample of 20 exoplanets to other worlds in our galactic neighborhood. As of late last year, astronomers have confirmed detections of more than 6,000 exoplanets.

“With a well-corrected spectrum, we can say there’s water, there’s nitrogen,” Quintana said. “So with every mission, as we evolve, we’re chipping away and taking bigger and bigger steps toward that question of, ‘OK, we know Earths are out there. We know they’re abundant. We know they have atmospheres. How do we know if they have life on them?’”

Building on a budget

A mission like Pandora was not possible until recently, certainly not on the $20 million budget NASA devoted to the project. With Pandora, the agency took advantage of a fast-growing small satellite industry churning out spacecraft at a fraction of what it cost 10 or 15 years ago.

The Pandora spacecraft weighed approximately 716 pounds (325 kilograms) at launch and likely would have required a dedicated rocket to travel to space before SpaceX started offering shared rides on its workhorse Falcon 9 rocket. NASA did not disclose what it paid SpaceX to launch Pandora, but publicly available pricing suggests SpaceX charges a few million dollars to launch a satellite of the same size. Before the rideshare option became available, NASA would have paid tens of millions of dollars for the launch alone.

The Pandora mission is part of NASA’s Astrophysics Pioneers program, an initiative set up to solicit ideas for lower-cost astronomy missions.

“It’s been very, very challenging to try and squeeze this big amount of science into this small cost box, but that’s kind of what makes it fun, right?” Barclay told Ars. “We have to be pretty ruthless in making sure that we only fund the things we need to fund. We accept risk where we need to accept the risk, and at times we need to accept that we may need to give up performance in order to make sure that we hit the schedule and we hit the launch [schedule].”

It helps that Pandora’s 17-inch (45-centimeter) telescope comes from Lawrence Livermore National Laboratory in California, which had the technology on the shelf from a national security program. Pandora uses a small satellite platform from Blue Canyon Technologies, a Colorado company.

“There is no way we could have done Pandora 10 years ago,” Barclay said. “The small launch capabilities that come from companies like Rocket Lab and SpaceX and others meant that now the vendors of spacecraft buses and spacecraft instruments are able to push their costs down because they know that there’s a market for small missions out there. Other parts of the government are investing heavily in small spacecraft, and so that allows us on the science side to make use of that economies of scale.”

For comparison, the European Space Agency launched an exoplanet observatory about the same size as Pandora in 2019 at a cost of more than $100 million.

There are companies now looking at how to scale up production of larger satellites, too. Cheaper, heavy satellites could launch on new heavy- and super-heavy rockets like SpaceX’s Starship or Blue Origin’s New Glenn.

“I think it is an amazing capability to have for astrophysicists because science is moving fast,” Apai said. “Exoplanet science is changing. I would say every three or four years, we have breakthroughs. And the product keeps changing. We push the boundaries, and if you ever have to work with 20- or 25-year-long mission lifetimes, that really just limits progress.”

Stephen Clark is a space reporter at Ars Technica, covering private space companies and the world’s space agencies. Stephen writes about the nexus of technology, science, policy, and business on and off the planet.

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Runaway black hole mergers may have built supermassive black holes

astronomy, astrophysics, black holes, cosmology, James Webb Space Telescope, Science, supermassive black holes / Shannon Garcia / November 10, 2025

The researchers used cosmological simulations to recreate the first 700 million years of cosmic history, focusing on the formation of a single dwarf galaxy. In their virtual galaxy, waves of stars were born in short, explosive bursts as cold gas clouds collapsed inside a dark matter halo. Instead of a single starburst episode followed by a steady drizzle of star formation as Garcia expected, there were two major rounds of stellar birth. Whole swarms of stars flared to life like Christmas tree lights.

“The early Universe was an incredibly crowded place,” Garcia said. “Gas clouds were denser, stars formed faster, and in those environments, it’s natural for gravity to gather stars into these tightly bound systems.”

Those clusters started out scattered around the galaxy but fell in toward the center like water swirling down a drain. Once there, they merged to create one megacluster, called a nuclear star cluster (so named because it lies at the nucleus of the galaxy). The young galactic heart shone with the light of a million suns and may have set the stage for a supermassive black hole to form.

A simulation of the formation of the super-dense star clusters.

A seemingly simple tweak was needed to make the simulation more precise than previous ones. “Most simulations simplify things to make calculations more practical, but then you sacrifice realism,” Garcia said. “We used an improved model that allowed star formation to vary depending on local conditions rather than just go at a constant rate like with previous models.”

Using the University of Maryland’s supercomputing facility Zaratan, Garcia accomplished in six months what would have taken 12 years on a MacBook.

Some clouds converted as much as 80 percent of their gas into stars—a ferocious rate compared to the 2 percent typically seen in nearby galaxies today. The clouds sparkled to life, becoming clusters of newborn stars held together by their mutual gravity and lighting a new pathway for supermassive black holes to form extremely early in the Universe.

Chicken or egg?

Most galaxies, including our own, are anchored by a nuclear star cluster nestled around a supermassive black hole. But the connection between the two has been a bit murky—did the monster black hole form and then draw stars close, or did the cluster itself give rise to the black hole?

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Next-generation black hole imaging may help us understand gravity better

astrophysics, black hole, event horizon, Event Horizon Telescope, gravity, Physics, relativity, Science / Beth Washington / November 8, 2025

Right now, we probably don’t have the ability to detect these small changes in phenomena. However, that may change, as a next-generation version of the Event Horizon Telescope is being considered, along with a space-based telescope that would operate on similar principles. So the team (four researchers based in Shanghai and CERN) decided to repeat an analysis they did shortly before the Event Horizon Telescope went operational, and consider whether the next-gen hardware might be able to pick up features of the environment around the black hole that might discriminate among different theorized versions of gravity.

Theorists have been busy, and there are a lot of potential replacements for general relativity out there. So, rather than working their way through the list, they used a model of gravity (the parametric Konoplya–Rezzolla–Zhidenko metric) that isn’t specific to any given hypothesis. Instead, it allows some of its parameters to be changed, thus allowing the team to vary the behavior of gravity within some limits. To get a sense of the sort of differences that might be present, the researchers swapped two different parameters between zero and one, giving them four different options. Those results were compared to the Kerr metric, which is the standard general relativity version of the event horizon.

Small but clear differences

Using those five versions of gravity, they model the three-dimensional environment near the event horizon using hydrodynamic simulations, including infalling matter, the magnetic fields it produces, and the jets of matter that those magnetic fields power.

The results resemble the sorts of images that the Event Horizon Telescope produced. These include a bright ring with substantial asymmetry, where one side is significantly brighter due to the rotation of the black hole. And, while the differences are subtle between all the variations of gravity, they’re there. One extreme version produced the smallest but brightest ring; another had a reduced contrast between the bright and dim side of the ring. There were also differences between the width of the jets produced in these models.

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There could be “dark main sequence” stars at the galactic center

astronomy, astrophysics, Dark Matter, main sequence, Science, star evolution, stars / Mike M. / July 16, 2025

Dark matter particle and antiparticle collisions could make some stars immortal.

For a star, its initial mass is everything. It determines how quickly it burns through its hydrogen and how it will evolve once it starts fusing heavier elements. It’s so well understood that scientists have devised a “main sequence” that acts a bit like a periodic table for stars, correlating their mass and age with their properties.

The main sequence, however, is based on an assumption that’s almost always true: All of the energy involved comes from the gravity-driven fusion of lighter elements into heavier ones. However, three astrophysicists consider an alternative source of energy that may apply at the very center of our galaxy— energy released when dark matter particles and antiparticles collide and annihilate. While we don’t even know that dark matter can do that, it’s a hypothetical with some interesting consequences, like seemingly immortal stars, and others that move backward along the main sequence path.

Dark annihilations

We haven’t figured out what dark matter is, but there are lots of reasons to think that it is comprised of elementary particles. And, if those behave like all of the particles we understand well, then there will be both regular and antimatter versions. Should those collide, they should annihilate each other, releasing energy in the process. Given dark matter’s general propensity not to interact with anything, these collisions will be extremely rare except in locations with very high dark matter concentrations.

The only place that’s likely to happen is at the very center of our galaxy. And, for a while, there was an excess of radiation coming from the galactic core that people thought might be due to dark matter annihilations, although it eventually turned out to have a more mundane explanation.

At the extreme densities found within a light year of the supermassive black hole at the center of our galaxy, concentrations are high enough that these collisions could be a major source of energy. And so astronomers have considered what all that energy might do to stars that end up in a black hole’s orbit, finding that under the right circumstances, dark matter destruction could provide more energy to a star than fusion.

That prompted three astrophysicists (Isabelle John, Rebecca Leane, and Tim Linden) to try to look at things in an organized fashion, modeling a “dark main sequence” of stars as they might exist within a close proximity to the Milky Way’s center.

The intense gravity and radiation found near the galaxy’s core mean that stars can’t form there. So, anything that’s in a tight orbit had formed somewhere else before gravitational interactions had pushed it into the gravitational grasp of the galaxy’s central black hole. The researchers used a standard model of star evolution to build a collection of moderate-sized stars, from one to 20 solar masses at 0.05 solar mass intervals. These are allowed to ignite fusion at their cores and then shift into a dark-matter-rich environment.

Since we have no idea how often dark matter particles might run into each other, John, Leane, and Linden use two different collision frequencies. These determine how much energy is imparted into these stars by dark matter, which the researchers simply add as a supplement to the amount of fusion energy the stars are producing. Then, the stars are allowed to evolve forward in time.

(The authors note that stars that are thrown into the grasp of a supermassive black hole tend to have very eccentric orbits, so they spend a lot of time outside the zone where dark matter collisions take place with a significant frequency. So, what they’ve done is the equivalent of having these stars experience the energy input given their average orbital distance from the galaxy’s core. In reality, a star would spend some years with higher energy input and some years with lower input as it moves about its orbit.)

Achieving immortality

The physics of what happens is based on the same balance of forces that govern fusion-powered stars, but produces some very strange results. Given only fusion power, a star will exist at a balance point. If gravity compresses it, fusion speeds up, more energy is released, and that energy causes the star to expand outward again. That causes the density drop, slowing fusion back down again.

The dark matter annihilations essentially provide an additional source of energy that stays constant regardless of what happens to the star’s density. At the low end of the mass range the researchers considered, this can cause the star to nearly shut off fusion, essentially looking like a far younger star than it actually is. That has the effect of causing the star to move backward along the main sequence diagram.

The researchers note that even lighter stars could essentially get so much additional energy that they can’t hold together and end up dissipating, something that’s been seen in models run by other researchers.

As the mass gets higher, stars reach the point where they essentially give up on fusion and get by with nothing but dark matter annihilations. They have enough mass to hold together gravitationally, but end up too diffused for fusion to continue. And they’ll stay that way as long as they continue to get additional injections of energy. “A star like this might look like a young, still-forming star,” the authors write, “but has features of a star that has undergone nuclear fusion in the past and is effectively immortal.”

John, Leane, and Linden find that the higher mass stars remain dense enough for fusion to continue even in proximity to the galaxy’s black hole. But the additional energy kept that fusion happening at a moderate rate. They proceeded through the main sequence, but at a pace that was exceptionally slow, so that running the simulation for a total of 10 billion years didn’t see them change significantly.

The other strange thing here is that all of this is very sensitive to how much dark matter annihilation is taking place. A star that’s “immortal” at one average distance will progress slowly through the main sequence if its average distance is a light year further out. Similarly, stars that are too light to survive at one location will hold together if they are a bit further from the supermassive black hole.

Is there anything to this?

The big caution is that this work only looks at the average input from dark matter annihilation. In reality, a star that might be immortal at its average distance will likely spend a few years too hot to hold together, and then several years cooling off in conditions that should allow fusion to reignite. It would be nice to see a model run with this sort of pulsed input, perhaps basing it on the orbits of some of the stars we’ve seen that get close to the Milky Way’s central black hole.

In the meantime, John, Leane, and Linden write that their results are consistent with some of the oddities that are apparent in the stars we’ve observed at the galaxy’s center. These have two distinctive properties: They appear heavier than the average star in the Milky Way, and all seem to be quite young. If there is a “dark main sequence,” then the unusual heft can be explained simply by the fact that lower mass stars end up dissipating due to the additional energy. And the model would suggest that these stars simply appear to be young because they haven’t undergone much fusion.

The researchers suggest that we could have a clearer picture if we were able to spend enough time observing the stars at our galaxy’s core with a large enough telescope, allowing us to understand their nature and orbits.

Physical Review D, 2025. DOI: Not yet available (About DOIs).

John is Ars Technica’s science editor. He has a Bachelor of Arts in Biochemistry from Columbia University, and a Ph.D. in Molecular and Cell Biology from the University of California, Berkeley. When physically separated from his keyboard, he tends to seek out a bicycle, or a scenic location for communing with his hiking boots.

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Merger of two massive black holes is one for the record books

astronomy, astrophysics, black hole mergers, black holes, gravitational waves, LIGO/VIRGO/KAGRA, Physics, Science / Kelly Newman / July 15, 2025

Physicists with the LIGO/Virgo/KAGRA collaboration have detected the gravitational wave signal (dubbed GW231123) of the most massive merger between two black holes yet observed, resulting in a new black hole that is 225 times more massive than our Sun. The results were presented at the Edoardo Amaldi Conference on Gravitational Waves in Glasgow, Scotland.

The LIGO/Virgo/KAGRA collaboration searches the universe for gravitational waves produced by the mergers of black holes and neutron stars. LIGO detects gravitational waves via laser interferometry, using high-powered lasers to measure tiny changes in the distance between two objects positioned kilometers apart. LIGO has detectors in Hanford, Washington, and in Livingston, Louisiana. A third detector in Italy, Advanced Virgo, came online in 2016. In Japan, KAGRA is the first gravitational-wave detector in Asia and the first to be built underground. Construction began on LIGO-India in 2021, and physicists expect it will turn on sometime after 2025.

To date, the collaboration has detected dozens of merger events since its first Nobel Prize-winning discovery. Early detected mergers involved either two black holes or two neutron stars. In 2021, LIGO/Virgo/KAGRA confirmed the detection of two separate “mixed” mergers between black holes and neutron stars.

A tour of Virgo. Credit: EGO-Virgo

LIGO/Virgo/KAGRA started its fourth observing run in 2023, and by the following year had announced the detection of a signal indicating a merger between two compact objects, one of which was most likely a neutron star. The other had an intermediate mass—heavier than a neutron star and lighter than a black hole. It was the first gravitational-wave detection of a mass-gap object paired with a neutron star and hinted that the mass gap might be less empty than astronomers previously thought.

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New evidence that some supernovae may be a “double detonation”

astronomy, astrophysics, Science, supernova, Type Ia supernova, white dwarf / Shannon Garcia / July 3, 2025

Type Ia supernovae are critical tools in astronomy, since they all appear to explode with the same intensity, allowing us to use their brightness as a measure of distance. The distance measures they’ve given us have been critical to tracking the expansion of the Universe, which led to the recognition that there’s some sort of dark energy hastening the Universe’s expansion. Yet there are ongoing arguments over exactly how these events are triggered.

There’s widespread agreement that type Ia supernovae are the explosions of white dwarf stars. Normally, these stars are composed primarily of moderately heavy elements like carbon and oxygen, and lack the mass to trigger additional fusion. But if some additional material is added, the white dwarf can reach a critical mass and reignite a runaway fusion reaction, blowing the star apart. But the source of the additional mass has been somewhat controversial.

But there’s an additional hypothesis that doesn’t require as much mass: a relatively small explosion on a white dwarf’s surface can compress the interior enough to restart fusion in stars that haven’t yet reached a critical mass. Now, observations of the remains of a supernova provide some evidence of the existence of these so-called “double detonation” supernovae.

Deconstructing white dwarfs

White dwarfs are the remains of stars with a similar mass to our Sun. After having gone through periods during which hydrogen and helium were fused, these tend to end up as carbon and oxygen-rich embers: hot due to their history, but incapable of reaching the densities needed to fuse these elements. Left on their own, these stellar remnants will gradually cool.

But many stars are not left on their own; they exist in binary systems with a companion, or even larger systems. These companions can provide the material needed to boost white dwarfs to the masses that can restart fusion. There are two potential pathways for this to happen. Many stars go through periods where they are so large that their gravitational pull is barely enough to hold on to their outer layers. If the white dwarf orbits closely enough, it can pull in material from the other star, boosting its mass until it passes a critical threshold, at which point fusion can restart.

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Simulations find ghostly whirls of dark matter trailing galaxy arms

astronomy, astrophysics, Dark Matter, galaxies, Science, simulations / Shannon Garcia / June 7, 2025

“Basically what you do is you set up a bunch of particles that represent things like stars, gas, and dark matter, and you let them evolve for millions of years,” Bernet says. “Human lives are much too short to witness this happening in real time. We need simulations to help us see more than the present, which is like a single snapshot of the Universe.”

Several other groups already had galaxy simulations they were using to do other science, so the team asked one to see their data. When they found the dark matter imprint they were looking for, they checked for it in another group’s simulation. They found it again, and then in a third simulation as well.

The dark matter spirals are much less pronounced than their stellar counterparts, but the team noted a distinct imprint on the motions of dark matter particles in the simulations. The dark spiral arms lag behind the stellar arms, forming a sort of unseen shadow.

These findings add a new layer of complexity to our understanding of how galaxies evolve, suggesting that dark matter is more than a passive, invisible scaffolding holding galaxies together. Instead, it appears to react to the gravity from stars in galaxies’ spiral arms in a way that may even influence star formation or galactic rotation over cosmic timescales. It could also explain the relatively newfound excess mass along a nearby spiral arm in the Milky Way.

The fact that they saw the same effect in differently structured simulations suggests that these dark matter spirals may be common in galaxies like the Milky Way. But tracking them down in the real Universe may be tricky.

Bernet says scientists could measure dark matter in the Milky Way’s disk. “We can currently measure the density of dark matter close to us with a huge precision,” he says. “If we can extend these measurements to the entire disk with enough precision, spiral patterns should emerge if they exist.”

“I think these results are very important because it changes our expectations for where to search for dark matter signals in galaxies,” Brooks says. “I could imagine that this result might influence our expectation for how dense dark matter is near the solar neighborhood and could influence expectations for lab experiments that are trying to directly detect dark matter.” That’s a goal scientists have been chasing for nearly 100 years.

Ashley writes about space for a contractor for NASA’s Goddard Space Flight Center by day and freelances in her free time. She holds master’s degrees in space studies from the University of North Dakota and science writing from Johns Hopkins University. She writes most of her articles with a baby on her lap.

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Milky Way galaxy might not collide with Andromeda after all

Andromeda, astronomy, astrophysics, cosmology, galactic mergers, galaxies, milky way, Science / 9u50fv / June 3, 2025

100,000 computer simulations reveal Milky Way’s fate—and it might not be what we thought.

It’s been textbook knowledge for over a century that our Milky Way galaxy is doomed to collide with another large spiral galaxy, Andromeda, in the next 5 billion years and merge into one even bigger galaxy. But a fresh analysis published in the journal Nature Astronomy is casting that longstanding narrative in a more uncertain light. The authors conclude that the likelihood of this collision and merger is closer to the odds of a coin flip, with a roughly 50 percent probability that the two galaxies will avoid such an event during the next 10 billion years.

Both the Milky Way and the Andromeda galaxies (M31) are part of what’s known as the Local Group (LG), which also hosts other smaller galaxies (some not yet discovered) as well as dark matter (per the prevailing standard cosmological model). Both already have remnants of past mergers and interactions with other galaxies, according to the authors.

“Predicting future mergers requires knowledge about the present coordinates, velocities, and masses of the systems partaking in the interaction,” the authors wrote. That involves not just the gravitational force between them but also dynamical friction. It’s the latter that dominates when galaxies are headed toward a merger, since it causes galactic orbits to decay.

This latest analysis is the result of combining data from the Hubble Space Telescope and the European Space Agency’s (ESA) Gaia space telescope to perform 100,000 Monte Carlo computer simulations, taking into account not just the Milky Way and Andromeda but the full LG system. Those simulations yielded a very different prediction: There is approximately a 50/50 chance of the galaxies colliding within the next 10 billion years. There is still a 2 percent chance that they will collide in the next 4 to 5 billion years. “Based on the best available data, the fate of our galaxy is still completely open,” the authors concluded.

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Have we finally solved mystery of magnetic moon rocks?

asteroids, astrophysics, core dynamo, geology, magnetism, moon rocks, paleomagnetism, Science, the Moon / Mike M. / May 24, 2025

NASA’s Apollo missions brought back moon rock samples for scientists to study. We’ve learned a great deal over the ensuing decades, but one enduring mystery remains. Many of those lunar samples show signs of exposure to strong magnetic fields comparable to Earth’s, yet the Moon doesn’t have such a field today. So, how did the moon rocks get their magnetism?

There have been many attempts to explain this anomaly. The latest comes from MIT scientists, who argue in a new paper published in the journal Science Advances that a large asteroid impact briefly boosted the Moon’s early weak magnetic field—and that this spike is what is recorded in some lunar samples.

Evidence gleaned from orbiting spacecraft observations, as well as results announced earlier this year from China’s Chang’e 5 and Chang’e 6 missions, is largely consistent with the existence of at least a weak magnetic field on the early Moon. But where did this field come from? These usually form in planetary bodies as a result of a dynamo, in which molten metals in the core start to convect thanks to slowly dissipating heat. The problem is that the early Moon’s small core had a mantle that wasn’t much cooler than its core, so there would not have been significant convection to produce a sufficiently strong dynamo.

There have been proposed hypotheses as to how the Moon could have developed a core dynamo. For instance, a 2022 analysis suggested that in the first billion years, when the Moon was covered in molten rock, giant rocks formed as the magma cooled and solidified. Denser minerals sank to the core while lighter ones formed a crust.

Over time, the authors argued, a titanium layer crystallized just beneath the surface, and because it was denser than lighter minerals just beneath, that layer eventually broke into small blobs and sank through the mantle (gravitational overturn). The temperature difference between the cooler sinking rocks and the hotter core generated convection, creating intermittently strong magnetic fields—thus explaining why some rocks have that magnetic signature and others don’t.

Or perhaps there is no need for the presence of a dynamo-driven magnetic field at all. For instance, the authors of a 2021 study thought earlier analyses of lunar samples may have been altered during the process. They re-examined samples from the 1972 Apollo 16 mission using CO₂ lasers to heat them, thus avoiding any alteration of the magnetic carriers. They concluded that any magnetic signatures in those samples could be explained by the impact of meteorites or comets hitting the Moon.

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A star has been destroyed by a wandering supermassive black hole

astronomy, astrophysics, black holes, Science, spaghettification, supermassive black hole, tidal disruption / DJ Henderson / May 9, 2025

But note the phrasing there: “in most cases” and “eventually.” Even in the cases where a merger takes place, the process is slow, potentially taking millions or even billions of years. As a result, a large galaxy might have as many as 100 extremely large black holes wandering about, with about 10 of them having masses of over 10⁶ times that of the Sun. And the galaxy that AT2024tvd resides in is very large.

One consequence of all these black holes wandering about is that not all of them will end up merging. If two of them approach the central black hole at the same time, then it’s possible for gravitational interactions to eject the smallest of them at nearly the velocity needed to escape the galaxy entirely. As a result, for millions of years afterwards, these supermassive black holes may be found at quite a distance from the galaxy’s core.

At the moment, it’s not possible to tell which of these explanations account for AT2024tvd’s location. The galaxy it’s in doesn’t seem to have undergone a recent merger, but there is the potential for this to be a straggler from a far-earlier merger.

It’s notable that all of the galaxies where we’ve seen an off-center tidal disruption event are very large. The paper that describes AT2024tvd suggests this is no accident: larger galaxies mean more mergers in the past, and thus more supermassive black holes floating around the interior. They also suggest that off-center events will be the only ones we see in large galaxies. That’s because larger galaxies will have larger supermassive black holes at their center. And, once a supermassive black hole gets big enough, its event horizon is so far out that stars can pass through it before they get disrupted, and all the energetic release would take place inside the black hole.

Presumably, if you were close enough to see this happen, the star would just fade out of existence.

The arXiv. Abstract number: 2502.17661 (About the arXiv). To be published in The Astrophysical Journal Letters.

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3D map of exoplanet atmosphere shows wacky climate

astronomy, astrophysics, exoplanet atmospheres, exoplanets, Science, spectroscopy / Mike M. / February 19, 2025

Last year, astronomers discovered an unusual Earth-size exoplanet they believe has a hemisphere of molten lava, with its other hemisphere tidally locked in perpetual darkness. And at about the same time, a different group discovered a rare small, cold exoplanet with a massive outer companion 100 times the mass of Jupiter.

Meet Tylos

The different layers of the atmosphere on WASP-121b.

This latest research relied on observational data collected by the European South Observatory’s (ESO) Very Large Telescope, specifically, a spectroscopic instrument called ESPRESSO that can process light collected from the four largest VLT telescope units into one signal. The target exoplanet, WASP-121b—aka Tylos—is located in the Puppis constellation about 900 light-years from Earth. One year on Tylos is equivalent to just 30 hours on Earth, thanks to the exoplanet’s close proximity to its host star. Since one side is always facing the star, it is always scorching, while the exoplanet’s other side is significantly colder.

Those extreme temperature contrasts make it challenging to figure out how energy is distributed in the atmospheric system, and mapping out the 3D structure can help, particularly with determining the vertical circulation patterns that are not easily replicated in our current crop of global circulation models, per the authors. For their analysis, they combined archival ESPRESSO data collected on November 30, 2018, with new data collected on September 23, 2023. They focused on three distinct chemical signatures to probe the deep atmosphere (iron), mid-atmosphere (sodium), and shallow atmosphere (hydrogen).

“What we found was surprising: A jet stream rotates material around the planet’s equator, while a separate flow at lower levels of the atmosphere moves gas from the hot side to the cooler side. This kind of climate has never been seen before on any planet,” said Julia Victoria Seidel of the European Southern Observatory (ESO) in Chile, as well as the Observatoire de la Côte d’Azur in France. “This planet’s atmosphere behaves in ways that challenge our understanding of how weather works—not just on Earth, but on all planets. It feels like something out of science fiction.”

Nature, 2025. DOI: 10.1038/s41586-025-08664-1

Astronomy and Astrophysics, 2025. DOI: 10.1051/0004-6361/202452405 (About DOIs).

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