Dense Dark Matter Clump, Not Supermassive Black Hole, May Reside at Milky Way's Center

Argentina - Ekhbary News Agency

Dense Dark Matter Clump, Not Supermassive Black Hole, May Reside at Milky Way's Center

For years, the prevailing scientific consensus has been that a supermassive black hole (SMBH) anchors the center of the Milky Way galaxy. Ample evidence supports the presence of this object, designated Sagittarius A-star (Sgr A*), at the Galactic Center (GC). However, lingering questions and alternative theories have persisted regarding its precise nature.

There is no doubt that an extraordinarily massive entity resides in the GC, and that is precisely the definition of an SMBH. Some of the most compelling evidence for such a massive object comes from the peculiar orbits of stars known as 'S-stars'. Their rapid trajectories around the GC strongly indicate the presence of an SMBH possessing approximately four million solar masses. Additionally, 'G-sources' – massive gas clouds – have been observed in the region, and their orbital paths also signal the influence of a colossal object. The acquisition of an image of the SMBH's shadow, surrounded by hot, orbiting material, by the Event Horizon Telescope (EHT) in 2022 seemed to solidify this view.

Despite this strong evidence, the scientific community is not universally convinced. Buried within the extensive scientific literature are numerous research efforts proposing that, instead of a black hole, a massive object composed of bosons or, more recently, dark matter fermions, might occupy the Milky Way's GC. New research, published in the prestigious journal 'Monthly Notices of the Royal Astronomical Society', lends significant weight to this alternative idea. The study posits that what truly resides at the galactic core is a massive concentration of fermionic dark matter.

The research paper, titled "The dynamics of S-stars and G-sources orbiting a supermassive compact object made of fermionic dark matter," is led by Valentina Crespi from the Institute of Astrophysics La Plata in Argentina. The authors state, "Surrounding Sgr A-star, a cluster of young and massive stars coexist with a population of dust-enshrouded objects, whose astrometric data can be used to scrutinize the nature of Sgr A-star." They further elaborate on the alternative scenario: "An alternative to the black hole (BH) scenario has been recently proposed in terms of a supermassive compact object composed of self-gravitating fermionic dark matter (DM)."

The fermionic matter explanation posits that dark matter can account for the observed stellar motions just as effectively as an SMBH. This model suggests that dark matter forms a structure characterized by a dense core and a diluted halo (dense core–diluted halo morphology). Such a structure, the researchers argue, can explain both the observed orbits of the S-stars and the galaxy's overall rotation curve, as meticulously mapped by the Gaia space observatory. Crucially, this dark matter hypothesis can also account for the shadow-like features captured in the EHT's image of Sagittarius A*. The research paper confirms this, stating that the fermion dark matter explanation "can also produce shadow-like features with sizes compatible with the measurements of the EHT collaboration when applied to Milky Way-like galaxies."

Fermions are fundamental subatomic particles, often described as 'light'. They can be elementary, like quarks and leptons, or composite, comprising particles like baryons, atoms, and atomic nuclei. Protons and neutrons, the building blocks of ordinary matter, are also composite fermions. The key principle governing fermions is the Pauli exclusion principle. This principle prevents them from collapsing into an infinitely dense point (a singularity). However, it does not preclude them from forming an object sufficiently dense and massive to generate the gravitational pull observed, thereby explaining the S-star and G-cloud orbits and other phenomena typically attributed to an SMBH.

The researchers propose that these hypothetical dark fermions do not interact via the electromagnetic force. Instead, their interactions are purely gravitational, mirroring the known behavior of dark matter. Dark fermions are the same type of particles theorized to form the dark matter halos surrounding galaxies. The researchers suggest that under specific conditions, these particles could aggregate into extremely dense concentrations at the centers of galaxies, effectively mimicking what we currently identify as SMBHs.

In their study, the team investigated two specific types of fermions, characterized by their masses: 56 keV and 300 keV. The 56 keV fermions resulted in a less compact core structure, while the 300 keV fermions yielded a more compact core. Both models proved capable of replicating the observed orbital parameters of the S-stars and G-clouds, with deviations of less than one percent when compared to models based on black holes.

Ekhbary News Agency