Cosmological black holes are not described by the Thakurta metric: LIGO-Virgo bounds on PBHs remain unchanged

TL;DR

This paper demonstrates that the Thakurta metric does not accurately describe cosmological black holes, confirming that existing LIGO-Virgo bounds on primordial black holes remain valid and unaffected by this model.

Contribution

The study clarifies that the Thakurta metric is not suitable for modeling cosmological black holes, reinforcing the validity of current primordial black hole constraints.

Findings

Thakurta metric does not apply to cosmological black holes.

Black hole mass growth cannot be supported by radiation, dark matter, or primordial black holes.

Existing LIGO-Virgo and CMB constraints on PBHs remain valid.

Abstract

We show that the physical conditions which induce the Thakurta metric, recently studied by B{\oe}hm {\it et al.} in the context of time-dependent black hole masses, correspond to a single accreting black hole in the entire Universe filled with isotropic non-interacting dust. In such a case, the physics of black hole accretion is not local but tied to the properties of the whole Universe. We show that radiation, primordial black holes or particle dark matter cannot produce the specific energy flux required for supporting the mass growth of Thakurta black holes. In particular, this solution does not apply to black hole binaries. We conclude that cosmological black holes and their mass growth cannot be described by the Thakurta metric, and thus existing constraints on the primordial black hole abundance from the LIGO-Virgo and the CMB measurements remain valid.