Is An Object Present At The Center of the Milky Way: A Black Hole Or A Dark Compact Object? (Cosmology)

Becerra-Vergara and colleagues in their recent paper, explored the possibility of an alternative nature of Sagittarius A*. By using the astrometry data of 17 best-resolved S-stars, they suggested that, instead of a supermassive black hole, it is a dark compact object having a dense core of darkinos, which are neural massive dark matter fermions. Their study recently appeared in the journal Monthly Notices of the Royal Astronomical Society: Letters.

Sagittarius A* is a bright and very compact astronomical radio source at the Galactic Center of the Milky Way. It has been long thought by scientific community that it is a supermassive black hole. This inference on the nature of Sgr A* mainly comes from the nearly Keplerian orbits of tens of stars belonging to the S-star cluster, whose motions are well described by geodesics in the Schwarzschild spacetime geometry.

The most important S-cluster member is S2 which, with an orbital period of about 16 yr and a pericenter of about 1500 Schwarzschild radii, has the most-compact orbit around Sgr A. The S2 orbit data have allowed to test General Relativity predictions such as the relativistic redshift and precession. But, astrophysicists were also confronted with a problem: they could not able to explain G2 motion, which is a gas cloud. This cloud reached so close to Sagittarius A* that it should have been destroyed or pulled in by the black hole. But, instead, it continued on its way, unharmed.

In this view, Becerra-Vergara and colleagues now explored the possibility of an alternative nature of Sgr A based on fermionic DM profile predicted by the Ruffini-Argüelles-Rueda (RAR) model.

They suggested, the reason G2 was able to survive its journey past Sagittarius A*, was because Sagittarius A* is not a black hole, instead, it is a compact object made up of dark matter.

To come to this conclusion, they ran a simulation of the Milky Way, in which Sagittarius A* was replaced by dark compact object composed of darkinos. They showed for the first time that, this dark compact object at the Galactic center can explain the G2 motion and the dynamics of the S-stars with similar (and some cases better) accuracy compared to a central BH model.

“Our results strengthen the alternative nature of Sgr A* as a dense quantum core of darkinos superseding the central massive BH scenario.”

In addition, an interesting fact they found is that, this dense core of darkinos also explains the rotation curves of the Milky Way. For particle masses ∼ 100 keV, the core radius shrinks from 0.4 mpc to a few Schwarzschild radii, so the gravitational potential produced by a central BH of mass MBH and a (RAR) DM core of mass, Mc = MBH, practically coincide for r ≳ 10 GM_BH/c². Therefore, the dynamics of baryonic matter at these scales should not differ much in the two scenarios. In simple terms, you can say, this dark compact object would have very similar characteristics compared to a black hole.

Reference: E A Becerra-Vergara, C R Argüelles, A Krut, J A Rueda, R Ruffini, Hinting a dark matter nature of Sgr A* via the S-stars, Monthly Notices of the Royal Astronomical Society: Letters, 2021;, slab051,

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