# Spins of black holes in coalescing compact binaries

## TL;DR

This paper reviews methods for measuring black hole spins, analyzes effective spins in various binary systems from LIGO/Virgo data, and models their distributions considering different formation scenarios and cosmic evolution.

## Contribution

It provides a comprehensive analysis of black hole spin distributions in coalescing binaries, incorporating stellar evolution models and comparing with gravitational wave observations.

## Key findings

- Calculated spin distributions align with LIGO/Virgo data.
- Primordial black holes can attain a few percent spin from accretion.
- Effective spins vary across binary types and formation models.

## Abstract

Modern astrophysical methods of determination of spins of rotating stellar-mass black hole in close binaries and of supermassive black holes in active galactic nuclei are briefly discussed. Effective spins of coalescing binary black holes derived from LIGO/Virgo gravitational wave observations are specially addressed. We consider three types of coalescing binaries: double black holes, black hole-neutron star binaries and primordial double black holes. The effective spins of coalescing astrophysical binary black holes and black holes with neutron stars are calculated for two plausible models of black hole formations from stellar core collapses (without or with additional fallback from the stellar envelope) taking into account the stellar metallicity and star formation rate evolution in the Universe. The calculated distributions do not contradict the reported LIGO/Virgo observations. The effective spins of primordial coalescing stellar-mass black holes can reach a few per cent due to accretion spin-up in the cold external medium.