Dark Matter and the Early Formation of Supermassive Black Holes

TL;DR

This paper explores how dark matter, especially self-interacting and ultralight dark matter, may influence the early growth of supermassive black holes at high redshift, beyond traditional gas accretion and mergers.

Contribution

It introduces models where dark matter clustering impacts SMBH growth, highlighting the potential role of ultralight dark matter in early black hole formation.

Findings

Dark matter capture is insignificant if DM remains in a standard NFW profile.

Self-interacting dark matter clustering can facilitate SMBH growth to >10^7 M_sun by z=10.

Ultralight dark matter may uniquely affect SMBH evolution due to its large de Broglie wavelength.

Abstract

We investigate the growth of supermassive black holes (SMBHs) at high redshift ($z \ge 10$) from a combination of dark matter capture, black-hole mergers, and gas accretion. It has previously been shown that SMBHs can form by $z \approx 10$ via black-hole mergers, Eddington-limited Bondi gas accretion and tidal disruption events with stars within dense nuclear clusters. Here, we examine the degree to which the capture of collisionless dark matter by a growing SMBH may also contribute. We first consider models deduced from cosmological simulations of galaxy formation and central BH formation. We show that in the case that the dense nuclear star cluster forms by cooling and collapse of gas, while the DM remains in a standard NFW profile, the contribution from cold dark matter accretion is insignificant. However, we suggest models for which dark matter clustering can occur (possibly by self interaction). We show that such clustering may affect SMBH growth. In such cases, a small seed stellar-remnant black hole can more easily reach $> 10^7$ M$_{\odot}$ by $z = 10$ in the core of dense nuclear star clusters. This remains true for either cold dark matter or ultralight dark matter with the observationally inferred mass of $\sim 10^{-22}$ eV. We highlight the unique possible evolution of ULDM capture by the growing SMBH due to the fact that the ULDM de Broglie wavelength exceeds the initial nuclear star cluster half-mass radius.