For decades, the movement of stars near the center of our Milky Way galaxy has provided some of the most convincing evidence for the existence of a supermassive black hole. However, Dr. Valentina Crespi from the La Plata Institute of Astrophysics and her colleagues propose an innovative alternative: a compact object composed of self-gravitating fermion dark matter, which could equally explain the observed stellar motions.
The prevailing theory attributes the observational orbits of a group of stars, known as the S stars, to Sagittarius A*, the supposed supermassive black hole at our galaxy’s center, which causes these stars to move at speeds of thousands of kilometers per second.
In a groundbreaking study, Dr. Crespi and her team propose that fermions—a specific type of dark matter made from light elementary particles—can form a distinct cosmic structure that aligns with our current understanding of the Milky Way’s core.
The hypothesis suggests the formation of an ultra-dense core surrounded by a vast, diffuse halo, functioning as a unified structure.
This dense core could replicate the gravitational effects of a black hole, thereby accounting for the orbits of S stars and nearby dusty objects known as G sources.
A vital aspect of this research includes recent data from ESA’s Gaia DR3 mission, which meticulously maps the Milky Way’s outer halo and reveals the orbital patterns of stars and gas far from the center.
The mission has documented a slowdown in the galaxy’s rotation curve, known as Keplerian decay, which can be reconciled with the outer halo of the dark matter model when combined with the standard disk and bulge components of normal matter.
This finding emphasizes significant structural differences, bolstering the validity of the fermion model.
While traditional cold dark matter halos spread in a “power law” fashion, the fermion model predicts a more compact halo structure with a tighter tail.
“This research marks the first instance where a dark matter model effectively connects vastly different scales and explains the orbits of various cosmic bodies, including contemporary rotation curves and central star data,” remarked Carlos Arguelles of the La Plata Astrophysics Institute.
“We are not merely substituting black holes for dark objects. Instead, we propose that supermassive centers and galactic dark matter halos represent two manifestations of a single continuum of matter.”
Importantly, the team’s fermion dark matter model has already undergone rigorous testing.
A recent 2024 survey demonstrated that as the accretion disk illuminates these dense dark matter cores, it produces shadow-like features reminiscent of those captured by the Event Horizon Telescope (EHT) collaboration at Sagittarius A*.
“This point is crucial. Our model not only elucidates stellar orbits and galactic rotation but also aligns with the famous ‘black hole shadow’ image,” stated Crespi.
“A dense dark matter core bends light to such an extent that it forms a central darkness encircled by a bright ring, creating an effect similar to shadows.”
Astronomers performed a statistical comparison of the fermion dark matter model against traditional black hole models.
While current data on internal stars cannot definitively distinguish between the two theories, the dark matter model offers a cohesive framework to elucidate both the galaxy’s center (encompassing the central star and shadow) and the galaxy at large.
“Gathering more precise data from instruments like the GRAVITY interferometer aboard ESO’s Very Large Telescope in Chile, and searching for specific features of the photon ring, an essential characteristic of black holes that are absent in the dark matter nuclear scenario, will be crucial for testing the predictions of this innovative model,” the authors noted.
“The results of these discoveries have the potential to revolutionize our understanding of the fundamental nature of the Milky Way’s enigmatic core.”
The team’s research was published today in Royal Astronomical Society Monthly Notices.
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V. Crespi et al. 2026. Dynamics of S stars and G sources orbiting supermassive compact objects made of fermion dark matter. MNRAS 546 (1): staf1854; doi: 10.1093/mnras/staf1854
Source: www.sci.news
