SPACE/COSMOS
'Dark matter, not a black hole, could power Milky Way's heart'
Royal Astronomical Society
Our Milky Way galaxy may not have a supermassive black hole at its centre but rather an enormous clump of mysterious dark matter exerting the same gravitational influence, astronomers say.
They believe this invisible substance – which makes up most of the universe's mass – can explain both the violent dance of stars just light-hours (often used to measure distances within our own solar system) away from the galactic centre and the gentle, large-scale rotation of the entire matter in the outskirts of the Milky Way.
The new study has been published today in Monthly Notices of the Royal Astronomical Society (MNRAS).
It challenges the leading theory that Sagittarius A* (Sgr A*), a proposed black hole at the heart of our galaxy, is responsible for the observed orbits of a group of stars, known as the S-stars, which whip around at tremendous speeds of up to a few thousand kilometres per second.
The international team of researchers have instead put forward an alternative idea – that a specific type of dark matter made up of fermions, or light subatomic particles, can create a unique cosmic structure that also fits with what we know about the Milky Way's core.
It would in theory produce a super-dense, compact core surrounded by a vast, diffuse halo, which together would act as a single, unified entity.
The inner core would be so compact and massive that it could mimic the gravitational pull of a black hole and explain the orbits of S-stars that have been observed in previous studies, as well as the orbits of the dust-shrouded objects known as G-sources which also exist nearby.
Of particular importance to the new research is the latest data from the European Space Agency's GAIA DR3 mission, which has meticulously mapped the rotation curve of the Milky Way's outer halo, showing how stars and gas orbit far from the centre.
It observed a slowdown of our galaxy's rotation curve, known as the Keplerian decline, which the researchers say can be explained by their dark matter model's outer halo when combined with the traditional disc and bulge mass components of ordinary matter.
This, they add, strengthens the 'fermionic' model by highlighting a key structural difference. While traditional Cold Dark Matter halos spread out following an extended 'power law' tail, the fermionic model predicts a tighter structure, leading to more compact halo tails.
The research has been carried out by an international collaboration involving the Institute of Astrophysics La Plata in Argentina, International Centre for Relativistic Astrophysics Network and National Institute for Astrophysics in Italy, Relativity and Gravitation Research Group in Colombia and Institute of Physics University of Cologne in Germany.
"This is the first time a dark matter model has successfully bridged these vastly different scales and various object orbits, including modern rotation curve and central stars data," said study co-author Dr Carlos Argüelles, of the Institute of Astrophysics La Plata.
"We are not just replacing the black hole with a dark object; we are proposing that the supermassive central object and the galaxy's dark matter halo are two manifestations of the same, continuous substance."
Crucially, this fermionic dark matter model had already passed a significant test. A previous study by Pelle et al. (2024), also published in MNRAS, showed that when an accretion disk illuminates these dense dark matter cores, they cast a shadow-like feature strikingly similar to the one imaged by the Event Horizon Telescope (EHT) collaboration for Sgr A*.
"This is a pivotal point," said lead author Valentina Crespi, of the Institute of Astrophysics La Plata.
"Our model not only explains the orbits of stars and the galaxy's rotation but is also consistent with the famous 'black hole shadow' image. The dense dark matter core can mimic the shadow because it bends light so strongly, creating a central darkness surrounded by a bright ring."
The researchers statistically compared their fermionic dark matter model to the traditional black hole model.
They found that while current data for the inner stars cannot yet decisively distinguish between the two scenarios, the dark matter model provides a unified framework that explains the galactic centre (central stars and shadow), and the galaxy at large.
The new study paves the way for future observations. More precise data from instruments such as the GRAVITY interferometer, on the Very Large Telescope in Chile, and the search for the unique signature of photon rings – a key feature of black holes and absent in the dark matter core scenario – will be crucial to test the predictions of this new model, the authors say.
The outcome of these findings could potentially reshape our understanding of the fundamental nature of the cosmic behemoth at the heart of the Milky Way.
ENDS
Images & captions
Caption: Artistic representation of the Milky Way, where the innermost stars move at near relativistic speeds (defined as velocities that constitute a significant fraction of the speed of light, typically considered to be 10% or more) around a dense core of dark matter, with no black hole at the centre. At greater distances, the halo part of the same invisible dark matter distribution continues to shape the motions of stars in the outskirts of our galaxy, tracing the characteristic rotation curve.
Credit: Valentina Crespi et al.
Further information
The paper 'The dynamics of S-stars and G-sources orbiting a supermassive compact object made of fermionic dark matter' by V. Crespi et al. has been published in Monthly Notices of the Royal Astronomical Society. DOI: 10.1093/mnras/staf1854.
Notes for editors
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Journal
Monthly Notices of the Royal Astronomical Society
Article Title
The dynamics of S-stars and G-sources orbiting a supermassive compact object made of fermionic dark matter’
Article Publication Date
5-Feb-2026
Scientists find a black hole spewing more energy than the Death Star
A University of Oregon-led study is tracking the unusual astronomical event, giving a new view into the universe
University of Oregon
image:
Yvette Cendes at the Very Large Array, a large radio telescope facility in New Mexico
view moreCredit: Yvette Cendes, University of Oregon
A supermassive black hole with a case of cosmic indigestion has been burping out the remains of a shredded star for four years — and it’s still going strong, new research led by a University of Oregon astrophysicist shows.
Already, the jet shooting out of the black hole is a contender for one of the brightest, most energetic things ever detected in the universe. Scientists have now collected enough data on the unusual occurrence to predict that the stream of radio waves belching from the black hole will keep increasing exponentially before peaking in 2027.
“This is really unusual,” said Yvette Cendes, an astrophysicist at the UO who led the work. “I'd be hard-pressed to think of anything rising like this over such a long period of time.”
Cendes and her team reported their findings Feb. 5 in the Astrophysical Journal.
Astrophysicists have documented plenty of incidents where a star gets a little too close to a black hole and gets shredded by its gravitational field without going all the way across the event horizon, or the point of no return. It’s called a “tidal disruption event” because it’s caused by the same gravitational dynamics that create ocean tides on Earth.
In this case, though, the gravitational tug shreds a star in a process descriptively named “spaghettification.”
But a black hole emitting this much energy so many years after chewing up a star is unprecedented, Cendes said.
In 2018, when Cendes was a postdoctoral researcher at Harvard University, one of her lab mates noticed the tidal disruption event using an optical telescope. At the time, it was “the most boring, garden-variety event,” she said, so no one paid much attention.
But then, a few years later, Cendes caught something strange: Although the black hole hadn’t done much immediately after shredding a star, it was now emitting quite a lot of energy in radio waves.
Her curiosity piqued, Cendes and her colleagues began scrutinizing the black hole more closely. They initially reported the discovery in a 2022 paper in the Astrophysical Journal. Since then, they’ve kept monitoring it, and it’s continued to surprise them.
The object’s official scientific name is AT2018hyz, though Cendes prefers the nickname “Jetty McJetface,” a nod to the internet-famous British research vessel Boaty McBoatface.
In the latest paper, Cendes and her colleagues show that the energy emitted from the black hole has continued to rise sharply over the last few years. It’s now 50 times brighter than it was when originally detected in 2019.
Their calculations also suggest that the radiation from the star has been shooting out in one direction as a single jet. That could explain why it wasn’t initially detected, if the jet wasn’t aimed towards Earth, Cendes said. But they won’t know for sure until the energy peaks in a few years.
Cendes is a radio astronomer, so the strong energy she’s measuring from the black hole is in the form of radio waves. (The region around the black hole is also emitting visible light, but it’s very faint.) Her team uses data collected at big radio telescopes in New Mexico and South Africa that measure radiation from around the universe at very high sensitivities.
They calculated the current energy outflow of the black hole and came up with an astounding number, putting it on a par with a gamma ray burst and potentially placing it among the most powerful single events ever detected in the universe.
To put it in other terms: Avid Star Wars fans have done calculations of how much energy the infamous super-powerful Death Star would emit. This black hole is emitting at least a trillion times that, and possibly closer to 100 trillion times.
Of course, only time will tell how high it will go. Her team is continuing to track the object to see whether their predictions play out.
Meanwhile, Cendes is on the hunt for other black holes that might also be exhibiting the phenomenon. No one has ever seen anything like this before, but that could be in part because nobody has really looked, she noted.
Securing time to gather data on international telescopes is competitive, Cendes said, and “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?”
But now they know to look.
— By Laurel Hamers, University Communications
Caption
An artistic representation of a tidal disruption event, or a black hole shredding a star.
Credit
DESY, Science Communication Lab
Article Title
Continued Rapid Radio Brightening of the Tidal Disruption Event AT2018hyz
Article Publication Date
5-Feb-2026
HKU and UCLA scientists uncover the mechanism powering “space battery” above auroral regions
The University of Hong Kong
image:
Comparative schematic of auroral acceleration processes on Earth and Jupiter. The electron spectrum for the Earth was from DMSP F19 spacecraft, and the one for Jupiter was from Juno spacecraft. Both spectra exhibit a similar inverted V-shaped structure, indicating the presence of stable electric potential drops above the auroral regions. This similarity points to a common auroral acceleration mechanism across planets and illustrates how insights from planetary aurorae help interpret high-resolution observations near Earth.
view moreCredit: S. Tian and Z. Yao
The dazzling lights of the aurora are created when high-energy particles from space collide with Earth’s atmosphere. While scientists have long understood this process, one big mystery remained: What powers the electric fields that accelerate these particles in the first place?
A new study co-led by the Department of Earth and Planetary Sciences at The University of Hong Kong (HKU) and the Department of Atmospheric and Oceanic Sciences at the University of California, Los Angeles (UCLA) now provided an answer. Published in Nature Communications, the research reveals that Alfvén waves — plasma waves travelling along Earth’s magnetic field lines — act like an invisible power source, fueling the stunning auroral displays we see in the sky.
By analysing how charged particles move and gain energy in different regions of space, the researchers demonstrated that these waves act as a natural accelerator, supplying energy that drives charged particles down into the atmosphere and produces the glowing auroral lights.
To confirm their findings, the team analysed data collected by multiple satellites orbiting Earth, including NASA's Van Allen Probes and the THEMIS mission. The data provided solid evidence that Alfvén waves continuously transfer energy to the auroral acceleration region, maintaining the electric fields that would otherwise dissipate.
“This discovery not only provides a definitive answer to the physics of Earth’s aurora, but also offers a universal model applicable to other planets in our solar system and beyond,” said Professor Zhonghua YAO of the Department of Earth and Planetary Sciences at HKU. Professor Yao leads a dedicated team in space and planetary science at HKU, which has established a reputation for high-impact research on planetary auroras.
With deep expertise in the magnetospheric dynamics of planets like Jupiter and Saturn, the HKU team brought a critical planetary perspective to the study. “Our team at HKU has long focused on the auroral processes of giant planets. By applying this knowledge to the high-resolution data available near Earth, we have bridged the gap between Earth science and planetary exploration.” Professor Yao added.
The research represents a model of interdisciplinary collaboration. The UCLA team, led by Dr Sheng TIAN, contributed extensive expertise in Earth’s auroral physics, while the HKU team provided the broader context of planetary space physics.
The full research paper can be read at: https://www.nature.com/articles/s41467-025-65819-4
For media enquiries, please contact HKU Faculty of Science (tel: 852-3917 4948/ 3917 5286; email: caseyto@hku.hk / cindycst@hku.hk ).
Images download and captions: https://www.scifac.hku.hk/press
Journal
Nature Communications
Method of Research
Observational study
Subject of Research
Not applicable
Article Title
Evidence for Alfvén waves powering auroral arc via a static electric potential drop
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