Constraints on Stupendously Large Black Holes

TL;DR

This paper investigates observational constraints on extremely large black holes, called SLABs, in the mass range of 10^{11} to 10^{18} solar masses, exploring their possible existence and implications for dark matter and fundamental physics.

Contribution

It provides the first comprehensive analysis of constraints on SLABs in the ultra-massive range, considering various astrophysical and particle physics effects.

Findings

Constraints from dynamical and lensing effects limit SLAB abundance.

Background radiation from gas accretion constrains SLAB formation.

Gamma-ray signals from WIMP annihilation around SLABs provide additional limits.

Abstract

We consider the observational constraints on stupendously large black holes (SLABs) in the mass range $M \gtrsim 10^{11}\,M_{\odot}$. These have attracted little attention hitherto and we are aware of no published constraints on a SLAB population in the range $(10^{12}$ - $10^{18})\,M_{\odot}$. However, there is already evidence for black holes of up to nearly $10^{11}\,M_{\odot}$ in galactic nuclei, so it is conceivable that SLABs exist and they may even have been seeded by primordial black holes. We focus on limits associated with (i) dynamical and lensing effects, (ii) the generation of background radiation through the accretion of gas during the pregalactic epoch, and (iii) the gamma-ray emission from the annihilation of the halo of weakly interacting massive particles (WIMPs) expected to form around each SLAB if these provide the dark matter. Finally, we comment on the constraints on the mass of ultra-light bosons from future measurements of the mass and spin of SLABs.