Dark Matter and the Early Formation of Supermassive Black Holes

Abstract We investigate the growth of supermassive black holes (SMBHs) at high redshift ( z ≥ 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 ≈ 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 black hole formation. We show that in the case in which the dense nuclear star cluster forms by cooling and collapse of gas, while the dark matter remains in a standard Navarro–Frenk–White profile, the contribution from cold dark matter (CDM) 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 ⊙ by z = 10 in the core of dense nuclear star clusters. This remains true for either CDM or ultralight dark matter (ULDM) with the observationally inferred mass of ∼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.