Daring Theory Challenges the Black Hole’s Reign Over the Milky Way’s Core

• Dealing with the invisible
• A core of dark matter
• Okay, so what?

Astronomers have yet to fully grasp the Galactic Center—the heart of the Milky Way—although they’re fairly certain that Sagittarius A*, a supermassive black hole, exists and dictates the cosmic objects in its vicinity. But a new study proposes the black hole might not be as influential as we believe. Instead, the dominant force in charge may be a huge clump of invisible matter.

The paper, published today in Monthly Notices of the Royal Astronomical Society, isn’t disavowing Sagittarius A*—scientists have, after all, found ample evidence that it’s real. Rather, the researchers challenge the theory that the supermassive black hole effectively controls the observed orbits of S-stars, a group of fast-spinning stars at the Galactic Center. Instead, they demonstrate that a dense, compact core of dark matter—the invisible matter thought to comprise some 85% of the universe’s mass—could easily mimic the gravitational pull of a black hole, in addition to better representing certain unexplained observations of the Galactic Center.

“This is the first time a dark matter model has successfully bridged these vastly different scales and various object orbits,” Carlos Argüelles, study co-author and an astrophysicist at the Institute of Astrophysics La Plata in Argentina, said in a statement.

Dealing with the invisible

Black holes and dark matter have some parallels. Neither are known to emit light, so we effectively are unable to “see” them. Instead, we’re clued into their existence by how they affect the stuff around them that we can see.

Of course, while scientists have found solid evidence for black holes, the same cannot be said of dark matter. Still, scientists have ample reason to believe dark matter exists and supports the various forces holding our universe in one piece. As the “missing” mass of the universe, it should exert significant influence over every corner of the cosmos—an idea that served as a starting point for the new study.

A core of dark matter

For the study, the team ran simulations that compared the feasibility of their dark matter model as opposed to the traditional black hole model. In theory, the core would produce a “super-dense, compact core surrounded by a vast, diffuse halo” of light—subatomic particles acting as a single entity, explained the researchers.

The simulations gave the researchers several predictions of orbital parameters for residents of the Galactic Center, including S-stars and a population of gassy clouds called G-sources. To their surprise, the two models’ predictions differed by less than 1%, confirming that—statistically speaking—a dark matter core made just as much sense as a supermassive black hole.

This similarity is consistent with black hole “shadow” images, since the dense dark matter core would bend light strongly, just like a black hole, creating a similar apparition.

What’s more, this particular model proved to be a good fit for recent observations of the Milky Way’s outer halo, which shows how stars and gas orbit far from the Galactic Center. The physics of a fermionic dark matter core supports recent observations from the European Space Agency’s GAIA DR3 mission, which observed a slowdown of the Milky Way’s rotation curve, the researchers said.

Okay, so what?

All that said, the team still has a lot more to prove if it hopes to usurp Sagittarius A* as the big boss of the Galactic Center. As they admit in the new paper, the dark matter model wasn’t conclusively better than the dominant black hole model, although it came pretty close. Of course, there’s also the giant issue that we have yet to actually find dark matter—and, for that matter, whether it would take the specific type used in the model.

The researchers anticipate that the new data from next-generation instruments will help to further scrutinize the model. And if they do end up finding something big, astrophysics may be in for a huge treat.