Spin of Primordial Black Holes

Abstract

Primordial black holes, formed from rare peaks in the primordial fluctuations $\zeta$, are non-rotating at zeroth order in ${\zeta }_{\mathrm{rms}}$. We show that the spin also vanishes at first order in ${\zeta }_{\mathrm{rms}}$, suggesting the dimensionless spin parameter $a_{\mathrm{rms}}\sim {\zeta }_{\mathrm{rms}}^2$. We identify one quadratic contribution to the spin by calculating (and extrapolating to the formation time) the torque on a black hole due to ambient acoustic waves. For a reasonable density of primordial black holes this implies a percent level spin parameter.

JCAP version. 21 pages, 2 figures