Signals of merging supermassive primordial black holes in pulsar timing arrays

TL;DR

This paper investigates whether merging primordial supermassive black holes could explain the gravitational wave background observed by pulsar timing arrays, considering constraints on their abundance and clustering effects.

Contribution

It analyzes the conditions under which primordial black hole mergers can account for pulsar timing array signals, highlighting the importance of clustering and formation constraints.

Findings

Homogeneous primordial black holes are inconsistent with observations due to abundance constraints.

Clustering can increase merger rates, potentially explaining the data.

Evading $bc$-distortion constraints is crucial for this interpretation.

Abstract

In this work we evaluate whether the gravitational wave background recently observed by a number of different pulsar timing arrays could be due to merging primordial supermassive black hole binaries. We find that for homogeneously distributed primordial black holes this possibility is inconsistent with strong cosmological and astrophysical constraints on their total abundance. If the distribution exhibits some clustering, however, the merger rate will, in general, be enhanced, opening the window for a consistent interpretation of the pulsar timing array data in terms of merging primordial black holes, if $\mu$-distortion constraints associated with the formation mechanism can be evaded.