Ultradense dark matter haloes accompany primordial black holes

TL;DR

This paper develops an analytic model showing that primordial black holes are accompanied by ultradense dark matter minihaloes, which could significantly impact observational tests of PBH dark matter scenarios.

Contribution

It introduces a new analytic framework for describing ultradense dark matter haloes formed alongside primordial black holes, altering previous predictions.

Findings

Ultradense haloes can contain an order-unity fraction of dark matter.

Even PBHs with a small fraction of dark matter are associated with dense haloes.

The results enable new observational tests for PBH dark matter models.

Abstract

Primordial black holes (PBHs) form from large-amplitude initial density fluctuations and may comprise some or all of the dark matter. If PBHs have a broadly extended mass spectrum, or in mixed PBH-particle dark matter scenarios, the extreme density fluctuations necessary to produce PBHs also lead to the formation of a much greater abundance of dark matter minihaloes that form during the radiation epoch with internal densities potentially of order $10^{12}$ M$_\odot$ pc$^{-3}$. We develop an analytic description of the formation of these ultradense haloes and use it to quantitatively compare PBH and halo distributions. PBHs that contribute only a per cent level fraction of the dark matter are accompanied by ultradense haloes that nevertheless comprise an order-unity fraction. These haloes would consist of either particle dark matter or much smaller PBHs. This finding significantly alters the predictions of many PBH scenarios, enabling a variety of new observational tests.