Mechanical feedback effects on primordial black hole accretion

Departament de Física Quàntica i Astrofísica, Institut de Ciències del Cosmos (ICC), Universitat de Barcelona (IEEC-UB), Martí i Franquès 1, 08028 Barcelona, Spain
e-mail: vbosch@fqa.ub.edu, nicola.bellomo@icc.ub.edu

Received: 20 January 2020
Accepted: 22 April 2020

Abstract

Context. Dark matter may consist, at least partially, of primordial black holes formed during the radiation-dominated era. The radiation produced by accretion onto primordial black holes leaves characteristic signatures on the properties of the medium at high redshift, before and after hydrogen recombination. Therefore, reliable modeling of accretion onto these objects is required to obtain robust constraints on their abundance.

Aims. We investigate the effect of mechanical feedback, that is, the impact of outflows (winds and– or –jets) on the medium, on primordial black hole accretion, and thereby on the associated radiation.

Methods. Using analytical and numerical calculations, we studied for the first time the possibility that outflows can reduce the accretion rate of primordial black holes with masses similar to those detected by the LIGO-Virgo collaboration.

Results. Despite the complexity of the accretion rate evolution, mechanical feedback is useful in to significantly reducing the primordial black hole accretion rate, at least by one order of magnitude, when outflows are aligned with the motion of the compact object. If the outflow is perpendicular to the direction of motion, the effect is less important, but it is still non-negligible.

Conclusions. Outflows from primordial black holes, even rather weak ones, can significantly decrease the accretion rate, effectively weakening abundance constraints on these objects. Our results motivate further numerical simulations with a more realistic setup, which would yield more precise quantitative predictions.