Bondi–Hoyle–Lyttleton accretion: on the roles of shape and redshift functions

Abstract

Matter-energy accretion phenomena onto astrophysical compact objects interpolate between local and global scales of our universe. In this paper, we will investigate the slow steady-state matter-energy accretion onto some black holes performing a comparative analysis with respect to both their gravitational potentials and for different accretion models whose applicability will be scrutinized. We will identify some mimicking of the Schwarzschild mass evolution and locations of the sonic critical points, the latter obtained via the continuity equation and the Bernoulli theorem. After analyzing these general features of the set-up, we will specialize to a cosmic matter supporting an emergent universe. Our analysis, fully based on exact analytical computations, will clarify the different roles of the small-scale astrophysical degrees of freedom, encoded in the black hole redshift and shape functions, versus the large-scale cosmological ones of the accreted material. Our manuscript tackles the intricate dynamics taking place across galactic and cosmological regimes, where screening mechanisms may occur, pointing out the required observational information for conclusively claiming the physical nature of an astrophysical compact object.