Gaia Data Release 3: Ellipsoidal Variables with Possible Black-Hole or Neutron Star secondaries

TL;DR

This paper identifies over 6,000 ellipsoidal binary candidates from Gaia DR3 data, suggesting many may host unseen compact objects like black holes or neutron stars, based solely on photometric variability and a novel mass ratio method.

Contribution

It introduces a new method to identify potential black hole or neutron star companions in binary systems using Gaia photometry without requiring primary star parameters.

Findings

6306 probable ellipsoidal variables identified

262 systems with high probability of compact secondary

Potential candidates for hosting black holes or neutron stars

Abstract

As part of Gaia Data Release 3, supervised classification identified a large number of ellipsoidal variables, for which the periodic variability is presumably induced by tidal interaction with a companion in a close binary system. In this paper, we present 6306 short-period probable ellipsoidal variables with relatively large-amplitude Gaia G-band photometric modulations, indicating a possible massive, unseen secondary. In case of a main-sequence primary, the more massive secondary is probably a compact object -- either a black hole or a neutron star, and sometimes a white dwarf. The identification is based on a robust modified minimum mass ratio (mMMR) suggested recently by Gomel, Faigler and Mazeh (2021), derived from the observed ellipsoidal amplitude only, without the use of the primary mass or radius. We also list a subset of 262 systems with mMMR larger than unity, for which the compact-secondary probability is higher. Follow-up observations are needed to verify the true nature of these variables.