The evolution of massive black holes and their spins in their galactic hosts

TL;DR

This paper models the mass and spin evolution of massive black holes within galaxy formation, considering gas effects during accretion and mergers, and predicts the gas-rich merger fraction over cosmic time for future gravitational wave observations.

Contribution

It introduces a self-consistent semi-analytical model for black hole evolution that incorporates detailed galaxy and gas dynamics, providing testable predictions for gravitational wave detectors.

Findings

Predicted the fraction of gas-rich black-hole mergers as a function of redshift.

Provided insights into spin alignment mechanisms during mergers.

Forecasted observational signatures for future space-based gravitational wave detectors.

Abstract

[Abridged] [...] We study the mass and spin evolution of massive black holes within a semianalytical galaxy-formation model that follows the evolution of dark-matter halos along merger trees, as well as that of the baryonic components (hot gas, stellar and gaseous bulges, and stellar and gaseous galactic disks). This allows us to study the mass and spin evolution of massive black holes in a self-consistent way, by taking into account the effect of the gas present in galactic nuclei both during the accretion phases and during mergers. Also, we present predictions, as a function of redshift, for the fraction of gas-rich black-hole mergers -- in which the spins prior to the merger are aligned due to the gravito-magnetic torques exerted by the circumbinary disk -- as opposed to gas-poor mergers, in which the orientation of the spins before the merger is roughly isotropic. These predictions may be tested by LISA or similar spaced-based gravitational-wave detectors such as eLISA/NGO or SGO.