Spins of primordial black holes formed in different cosmological scenarios

TL;DR

This paper explores how the spins of primordial black holes vary across different cosmological formation scenarios, highlighting the impact of formation mechanisms and radiative cooling on their angular momentum.

Contribution

It provides a comparative analysis of primordial black hole spins in various formation scenarios, emphasizing the role of scalar radiation in angular momentum removal.

Findings

Horizon-size collapse PBHs have very small spins.

Matterlike object assembly can produce PBHs with a range of spins.

Scalar radiation efficiently reduces angular momentum in certain scenarios.

Abstract

Primordial black holes (PBHs) could account for all or part of dark matter, as well as for some LIGO events. We discuss the spins of primordial black holes produced in different cosmological scenarios, with the emphasis on recently discovered possibilities. PBHs produced as a horizon-size collapse of density perturbations are known to have very small spins. In contrast, PBHs resulting from assembly of matterlike objects (particles, Q-balls, oscillons, etc.) can have large or small spins depending on their formation history and the efficiency of radiative cooling. We show that scalar radiation can remove the angular momentum very efficiently, leading to slowly rotating PBHs in those scenarios for which the radiative cooling is important. Gravitational waves astronomy offers an opportunity to determine the spins of black holes, opening a new window on the early Universe if, indeed, some black holes have primordial origin.