Aspects of Black Hole Physics and Formation of Super-massive Black Holes from Ultra-light Dark Bosons

Abstract

First, we verify that the physical parameters estimated for the four directly detected gravitational wave (GW) events involving coalescence of binary black holes (BHs) indeed uphold the second law of BH thermodynamics, strengthening further the case for BH physics. Non-spherical gravitational collapse leading to BH formation may entail very high GW luminosities during the final phase of implosion, reaching non-negligible fraction of Dyson luminosity $\sim c^5/G $. Most galaxies harbor supermassive black holes (SMBHs) in their nuclear regions. Several bright quasars detected at redshifts $\gtrsim$ 6 are powered by accreting SMBHs of mass $\gtrsim 10^9 M_\odot$ when the universe was only $\sim 10^9$ yrs old. We posit that creation of SMBHs occurs due to collapse (on dynamical time scales $\sim 10^8$ yrs) of ultra-light bosonic dark matter (DM) particles that have undergone Bose-Einstein condensation. Furthermore, oscillations in DM Bose-Einstein condensates (BECs) triggered by tidal forces in interacting galaxies can lead to bursts of star formation in the galactic nuclei because of frequent collisions of gas clouds due to changing gravitational field. We buttress our proposal by first employing simple but tangible physical arguments, and then by making use of Gross-Pitaevskii equation to study the formation of rotating SMBHs having mass $\gtrsim 10^9 M_\odot$. We also make simple estimates of GW amplitude as well as luminosity ensuing from the time varying configuration of BECs, constituted by the ultra-light dark bosons, and remark on the possibility of detecting such GWs using Pulsar Timing Arrays.