A team of researchers proposes that the supermassive black hole at the center of the Milky Way, known as Sagittarius A*, could actually be a dense clump of dark matter rather than a traditional black hole. Their model, based on fermionic dark matter particles, matches observations of stellar orbits and the 2022 Event Horizon Telescope image. However, many experts remain skeptical, favoring the black hole explanation.
At the heart of the Milky Way sits Sagittarius A*, a supermassive black hole that has long been a subject of intense study. Now, researchers from the National University of La Plata in Argentina, including Valentina Crespi and Carlos Argüelles, have proposed an alternative: this celestial object might be composed of dark matter.
Dark matter, which constitutes about 85 percent of the universe's matter and interacts only gravitationally, is known to form halos around galaxies. The team's model envisions a core of extremely light fermionic dark matter particles forming a massive, dense clump. From distant observations, such as those from Earth, this structure would appear nearly identical to a black hole. As Argüelles explains, “From Earth, you would see something very similar to what you would see in the black hole scenario – but if we went in a ship towards the centre, we could go through with no problem.”
The proposal draws on data from the orbits of nearby stars and gas clouds, the galaxy's overall rotation, and the glowing ring imaged by the Event Horizon Telescope in 2022. This ring, formed by superheated matter, could result from the gravitational influence of a dark matter core.
Skeptics, however, point to limitations. Gaston Giribet of New York University states, “Based on the fact that it is a simpler answer that fits the evidence, I personally believe that the celestial body at the center of our galaxy is very likely a black hole,” though he acknowledges the idea's interest. Shep Doeleman, founding director of the Event Horizon Telescope project at Harvard University, notes that the model fits observations several light-hours from the event horizon but raises questions closer in, where magnetic field patterns align with black hole expectations.
Furthermore, fermionic dark matter clumps are limited to about 10 million solar masses, while Sagittarius A* is far larger. The similar appearance of the much more massive M87* black hole, at 6.5 billion solar masses, challenges the theory. The researchers admit their idea is not more probable than a black hole and cannot yet be confirmed with current instruments. Higher-resolution imaging, potentially decades away, would be needed to distinguish between the two. If verified, such a discovery could upend models of cosmology, as fermionic dark matter deviates from standard predictions favoring heavier particles.