Speaker
Description
Non-linear structure formation for fermionic dark matter particles leads to dark matter density profiles with a degenerate compact core surrounded by a diluted halo. For a given fermion mass, the core has a critical mass that collapses into a supermassive black hole (SMBH). Galactic dynamics constraints suggest a 100 keV fermion as an excellent dark matter candidate, which leads to 10 million solar masses critical core mass. Here, we show that baryonic (ordinary) matter accretion drives an initially stable dark matter fermion core to SMBH formation and determine the accreted mass threshold that induces it. Baryonic gas density and velocity inferred from cosmological hydro-simulations and observations produce sub-Eddington accretion rates triggering the baryon-induced collapse in less than a Gyr. We show with specific (observational) examples that this process produces active galactic nuclei in galaxy mergers and the high-redshift Universe: the merging galaxy TXS 2116-077, the farthest SMBH at z=10.3 at the center of the galaxy UHZ1, and the "little red dots", the increasing population of SMBHs at z=4-6 revealed by the James Webb Space Telescope. After its formation, the SMBH can grow to a few billion solar masses in timescales shorter than a Gyr via sub-Eddington baryonic mass accretion. The baryon-induced collapse of dark matter fermion cores, by answering the long-standing question of how SMBHs form and grow in the high-z universe, adds a piece to the possible role of a yet-unobserved massive fermion in the Universe. It opens a research window verifiable especially with the JWST and Euclid data, to further constrain the fermionic dark matter hypothesis. These constraints, combined with information from galactic dynamics, strengthen the synergy between astrophysics and terrestrial laboratories of direct searches of a "light" dark matter particle at sub-MeV energies.
