Quantifying the evidence against a mass gap between black holes and neutron stars

TL;DR

This paper analyzes the mass distribution of compact objects and finds strong evidence against a strict mass gap between black holes and neutron stars, suggesting the gap may not be real.

Contribution

It provides a statistical evaluation of candidate objects within the mass gap, challenging the notion of an absolute mass gap.

Findings

No evidence for an absolute mass gap at high confidence

Candidates within the gap suggest it may be a statistical artifact

Implications for understanding compact object formation processes

Abstract

The lack of objects between $2\,M_{\odot}$ and $5\,M_{\odot}$ in the joint mass distribution of compact objects has been termed "mass gap", and attributed mainly to the characteristics of the supernova mechanism precluding their birth. However, recent observations show that a number of candidates reported to lie inside the "gap" may fill it, suggesting instead a paucity that may be real or largely a result of small number statistics. We quantify in this work the individual candidates and evaluate the joint probability of a mass gap. Our results show that an absolute mass gap is not present, to a very high confidence level. It remains to be seen if a relative paucity of objects stands in the future, and how this population can be related to the formation processes, which may include neutron star mergers, collapse of a neutron star to a black hole and others.