THE MULTIFACETED FORMATION OF BINARY BLACK HOLES

Michela Mapelli – University of Padova

The latest results from the LIGO-Virgo collaboration challenge the astrophysical scenarios of black hole formation. In this talk, I will discuss the main astrophysical formation channels of binary black holes. On the one hand, models of stellar evolution and pair instability supernovae suggest a gap in the mass spectrum of black holes between ~60 and ~120 Msun. The boundaries of this gap depend on stellar rotation and on the efficiency of envelope removal. On the other hand, extreme dynamical processes in dense star clusters can fill the mass gap, via multiple stellar collisions and dynamical exchanges. Moreover, stellar dynamics enhances the formation of black hole — neutron star systems with extreme (<1:10) mass ratios. Based on a data-driven model, I will discuss the merger history of dynamical versus isolated binary compact objects across cosmic time, and its dependence on the cosmic star formation rate and on the stellar metallicity.