Early formation of supermassive black holes from the collapse of strongly self-interacting dark matter

TL;DR

This paper explores how ultra-strongly self-interacting dark matter could lead to early supermassive black hole formation via gravothermal collapse, providing a potential explanation for high-redshift SMBHs.

Contribution

It introduces a novel scenario where strongly self-interacting dark matter causes early black hole seeds through gravothermal collapse, with detailed analysis of interaction parameters.

Findings

Bimodal parameter space for dark matter properties that can produce SMBHs

Rutherford-like self-interaction best explains observations

Predictions include intermediate mass black holes in smaller galaxies

Abstract

Evidence for high-redshift supermassive black holes challenges standard scenarios for how such objects form in the early universe. Here, we entertain the possibility that a fraction of the cosmological dark matter could be ultra-strongly self interacting. This would imply that gravothermal collapse occur at early times in the cores of dark matter halos, followed by accretion. We study under which conditions on the abundance and interaction strength and structure of such ultra self-interacting dark matter the black holes resulting from the end-point of gravothermal core collapse can seed the observed, early-forming supermassive black holes. We find, depending on the velocity dependence of the self-interaction cross section, a bimodal structure in the favored parameter space, where data points to either a small collapsing dark matter fraction with a large cross section, or a large fraction and a relatively small cross section. While self-interaction cross sections with different velocity dependence can explain observations, we find that the best, self-consistent results correspond to a Rutherford-like self-interaction, typical of long-range dark-sector forces with light mediators. We discuss complementary observational probes if this scenario is realized in nature, focusing especially on the expected intermediate mass black holes predicted to exist in smaller galaxies.