Astronomers suggest that the Milky Way's core might host a dense clump of fermionic dark matter rather than a supermassive black hole. This structure could explain the rapid orbits of nearby stars and the smoother rotation of distant material. The findings, published in Monthly Notices of the Royal Astronomical Society, challenge long-held views of Sagittarius A*.
For decades, scientists have attributed the intense gravitational pull at the Milky Way's center to Sagittarius A* (Sgr A*), a supermassive black hole. However, a new study proposes an alternative: an ultra-dense concentration of fermionic dark matter, composed of lightweight subatomic particles, forming a compact core surrounded by a diffuse halo.
This model accounts for the blistering speeds of the S stars, which orbit the galactic center at several thousand kilometres per second, just light hours from the core. It also explains the motion of nearby G sources, dust-covered objects, and the graceful rotation of stars and gas in the outer regions. Observations from the European Space Agency's GAIA DR3 mission reveal a Keplerian decline in orbital speeds at large distances, aligning with the predicted dark matter halo when combined with the galaxy's disk and bulge mass.
Unlike standard cold dark matter models, which forecast extended halos with power-law tails, the fermionic version produces a more compact structure with defined outer edges. The research, involving scientists from Argentina, Italy, Colombia, and Germany, integrates data on central orbits and the galaxy's rotation curve.
"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 co-author Dr. Carlos Argüelles of the Institute of Astrophysics La Plata. Lead author Valentina Crespi added, "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."
An earlier 2024 study showed that light bending around such a core mimics the Event Horizon Telescope's image of Sgr A*. Statistical comparisons with black hole models remain inconclusive with current data, but future tools like the GRAVITY interferometer on Chile's Very Large Telescope could detect photon rings—absent in the dark matter scenario—potentially resolving the debate.
If verified, this could redefine our understanding of the galaxy's heart as a continuous dark matter system rather than a discrete black hole.