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A recent paper (related news) shows that Sgr A* at the center of the Milky Way galaxy could be a dark matter core, instead of a supermassive black hole, according to their calculation using the astrometry data of the 17 best-resolved S-stars and the mysterious G2. The dark matter particles could be 56 keV fermions, which they call "darkinos".

The team also proposes that, above a critical mass, a dark matter clump could gravitationally collapse into a supermassive black hole, like the one in M87.

Is this dark matter model possible? Do the flares from Sgr A* observed in recent years support or contradict this model? Can LHC or other smaller particle colliders or detectors on Earth help to confirm or rule out the particle?

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  • $\begingroup$ Given that we're really pretty sure that many other galaxies contain SMBHs, it would seem at best unlikely that ours is somehow radically different. $\endgroup$
    – user38308
    May 21, 2021 at 16:59
  • $\begingroup$ @tfb The team also proposes that, above a critical mass, a dark matter clump could gravitationally collapse into a supermassive black hole. I have edited my question to reflect this. $\endgroup$
    – NeutronCat
    May 21, 2021 at 17:52

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I'm going to say, "probably not", because (as tfb points out) we have very good evidence for SMBHs in other galaxies -- in particular galaxies with active nuclei where the phenomenon associated with accretion disks around BHs are seen. The most extreme case is probably NGC 4395, where a Seyfert 1 nucleus and associated radio jets exist. The best estimates for accretion-disk+SMBH models suggest a SMBH mass of only a few hundred thousand solar masses; a recent direct dynamical measurement (den Brok et al. 2015) indicate a central "dark object" gravitational mass of $M_{\rm BH} \sim 400,000$ solar masses. There are numerous other galaxies with active nuclei where the estimated or measured central-object masses are $M_{\rm BH} \sim 10^{6}$--$10^{7} M_{\odot}$.

This is rather difficult to square with the claim that "above a critical mass, a dark matter clump could gravitationally collapse into a supermassive black hole" because if you follow up the associated reference to Argüelles et al. (2021), it ends up predicting a critical mass of $\sim 10^{8} M_{\odot}$. This is consistent with something like M87 ($M_{\rm BH} \sim 6 \times 10^{9} M_{\odot}$), but not with all the evidence for accreting SMBHs in galaxy centers with $M_{\rm BH} < 10^{7} M_{\odot}$.

The "flares observed from Sgr A* in recent years" are, I believe, generally supposed to be evidence for a very weak, transient accretion disk around the SMBH (e.g., the discussion on this web page), and so would be difficult to explain with this model.

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