Supermassive Black Holes from Ultra-Strongly Self-Interacting Dark Matter

TL;DR

This paper explores how a small fraction of ultra-strongly self-interacting dark matter can lead to early black hole formation, potentially explaining high-redshift quasars and addressing galaxy core issues.

Contribution

It introduces the idea that a minor component of ultra-strongly self-interacting dark matter can form seed black holes early, impacting cosmological structure formation.

Findings

uSIDM can undergo gravothermal collapse to form seed black holes

Black holes from uSIDM can grow to supermassive sizes by high redshift

Formation of black holes may resolve galaxy core and 'too big to fail' problems

Abstract

We consider the cosmological consequences if a small fraction ($f\lesssim 0.1$) of the dark matter is ultra-strongly self-interacting, with an elastic self-interaction cross-section per unit mass $\sigma\gg1\ \mathrm{cm^{2}/g}$. This possibility evades all current constraints that assume that the self-interacting component makes up the majority of the dark matter. Nevertheless, even a small fraction of ultra-strongly self-interacting dark matter (uSIDM) can have observable consequences on astrophysical scales. In particular, the uSIDM subcomponent can undergo gravothermal collapse and form seed black holes in the center of a halo. These seed black holes, which form within several hundred halo interaction times, contain a few percent of the total uSIDM mass in the halo. For reasonable values of $\sigma f$, these black holes can form at high enough redshifts to grow to $\sim10^9 M_\odot$ quasars by $z \gtrsim 6$, alleviating tension within the standard $\Lambda$CDM cosmology. The ubiquitous formation of central black holes in halos could also create cores in dwarf galaxies by ejecting matter during binary black hole mergers, potentially resolving the "too big to fail" problem.