Spins of primordial binary black holes before coalescence

Abstract

Primordial stellar-mass black holes, which may contribute to dark matter and to the observed LIGO binary black hole coalescences, are expected to be born with very low spins. Here we show that accretion mass gain by the components of a primordial black hole binary from the surrounding matter could lead to noticeable spins of the components prior to the coalescence provided high initial orbital eccentricities.

Comments: 11 pages, 5 figures, accepted to JCAP. Typo in Eq. (3.4) corrected, Fig. 4 substituted. No changes in the conclusions