Rescuing the primordial black holes all-dark matter hypothesis from the fast radio bursts tension

Abstract

Primordial black holes (PBHs) as an all-dark matter (DM) hypothesis has recently been demotivated by the prediction that these objects would source an excessive rate of fast radio bursts (FRBs). However, these predictions were based on several simplifying assumptions to which this rate is highly sensitive. In this article, we improve previous estimates of this rate arising from the capture of PBHs by neutron stars (NSs), aiming to revitalise this theory. We more accurately compute the velocity distribution functions of PBHs and NSs and also consider an enhancement in the NS and DM density profiles at galactic centers due to the presence of a central supermassive black hole. We find that previous estimates of the rate of FRBs sourced by the capture of PBHs by NSs were 3 orders of magnitude too large, concluding that the PBHs as all DM hypothesis remains a viable theory and that the observed FRB rate can only be entirely explained when considering a central, sufficiently spiky PBH density profile.