For decades, astronomers have believed that a supermassive black hole sits at the heart of our galaxy.
This object, known as Sagittarius A*, is thought to control the furious motion of stars near the Milky Way’s center and help shape the galaxy as a whole.
But a new study suggests a bold alternative: the Milky Way’s core might not be a black hole at all, but a dense clump of dark matter that behaves almost exactly like one.
The research, published in Monthly Notices of the Royal Astronomical Society, proposes that a special form of dark matter could explain both the extreme motions of stars close to the galactic center and the slower rotation of matter far out in the galaxy’s outer regions.
Dark matter is invisible and mysterious, but astronomers know it makes up most of the universe’s mass and strongly influences how galaxies form and move.
At the center of the Milky Way, a group of stars known as the S-stars orbit at astonishing speeds—thousands of kilometers per second—within a region only light-hours across.
These observations have long been considered strong evidence for a supermassive black hole. However, the new study shows that a compact core of dark matter could produce the same gravitational pull and explain the stars’ behavior just as well.
The researchers focus on a type of dark matter made of fermions, lightweight subatomic particles that follow quantum rules.
According to their model, this dark matter would naturally form a two-part structure: an extremely dense central core surrounded by a large, diffuse halo. The core would be small and massive enough to mimic a black hole, while the halo would extend far beyond the galaxy’s visible edge.
Crucial support for this idea comes from recent data collected by the European Space Agency’s Gaia mission.
Gaia’s latest data release mapped how stars and gas rotate in the Milky Way’s outer halo with unprecedented detail.
The observations show a gradual slowdown in rotation at large distances, a pattern known as a Keplerian decline.
The researchers found that this behavior fits naturally with the outer halo predicted by their fermionic dark matter model, when combined with the normal matter in the galaxy’s disk and bulge.
Remarkably, the model has also passed another important test. Previous work showed that a dense dark matter core, when surrounded by glowing material, could cast a dark “shadow” similar to the one imaged by the Event Horizon Telescope for Sagittarius A*.
Strong gravity near the core bends light in much the same way a black hole would, producing a dark center ringed by light.
The researchers emphasize that this does not yet disprove the black hole explanation. With current data, both models remain possible. However, the dark matter scenario has a unique advantage: it provides a single, unified explanation for the galaxy’s inner stars, its outer rotation, and even the observed shadow-like feature.
Future observations will be decisive. Instruments such as the GRAVITY interferometer on the Very Large Telescope may soon track stellar motions with enough precision to tell the difference.
Detecting—or failing to detect—certain light patterns known as photon rings could finally reveal whether the Milky Way’s heart is a true black hole or an exotic dark matter imposter.
Source: KSR.
