What sits at the center of the Milky Way? For decades, the standard answer has been clear. A supermassive black hole called Sagittarius A*. But a new peer-reviewed study now argues that the object at our galaxy’s core could instead be an ultra-compact concentration of dark matter, dense enough to pull nearby stars in almost the same way.
Even more striking, the same model could also help explain how the outer parts of the Milky Way rotate.
That is a big claim. It also comes with a big warning. Observations of stars crowding around Sagittarius A* have long pointed to a central object with a mass of about 4.297 million Suns, and in 2022 the Event Horizon Telescope unveiled the first image of Sagittarius A*, describing it as direct visual evidence of a black hole.
The new paper does not erase that evidence. Instead, it asks whether a dense, horizonless dark matter core could mimic much of the same behavior.
One invisible structure, from the center to the edge
The authors modeled Sagittarius A* not as a point of no return, but as a compact concentration of light subatomic particles called fermions. In their scenario, the Milky Way’s central object and its much larger dark matter halo are part of one continuous structure.
That matters because the model tries to fit both the tight orbits of the fast S-stars and nearby dusty G-objects, and the broader rotation pattern of the galaxy itself. As co-author Carlos Argüelles put it, “This is the first time a dark matter model has successfully bridged these vastly different scales and various object orbits.”
Why are astronomers paying attention? Because Gaia-based research has found a Keplerian decline in the Milky Way’s outer rotation curve, with speeds dropping by about 30 kilometers per second between 19.5 and 26.5 kiloparsecs from the galactic center.
The new fermionic model argues that a tighter, more compact halo can fit that slowdown better than more spread-out halo ideas. In practical terms, one invisible ingredient could be shaping both the frantic motion near Sagittarius A* and the slower sweep of the galaxy far beyond it.
The shadow still matters
This is where the story gets tricky. The black hole picture still has real weight behind it, especially the 2022 image of a dark central region surrounded by a bright ring.
But earlier research cited by the new paper found that dense fermionic cores can also create a central darkness with a ring-like feature when illuminated by an accretion disk. So that famous image, dramatic as it is, may not settle the argument all by itself.
The same caution shows up in the paper’s numbers. For the stars and G-objects tested so far, the standard black hole model and the fermionic dark matter model produce orbital parameters that differ by less than 1%. Current data, the authors say, are still not enough to decisively separate the two. So, is the old black hole story suddenly finished? Not yet.
What this paper really does is open the door wider to a rival explanation for what sits at the center of our galaxy.
Chile may help settle it
The next step is not more hype. It is better data. The study and the Royal Astronomical Society both point to increasingly precise observations from the GRAVITY instrument on ESO’s Very Large Telescope in Chile as one of the best ways to test the idea.
There is also a cleaner signature to watch for. Black holes are expected to produce photon rings, while fermionic dark matter cores should not. If astronomers can measure those rings clearly, the debate could shift very fast. And that is where the real tension begins.
If future observations fail to find those rings, or show motions that fit the dark matter core better, astronomy could be in for a major rethink. If they do find the expected black hole signatures, the traditional picture will only grow stronger. Either way, the heart of the Milky Way is still keeping some of its secrets.
The study was published in Monthly Notices of the Royal Astronomical Society.
Image credit: ESO/MPE/S. Gillessen et al.
