Triage of the Gaia DR3 astrometric orbits. I. A sample of binaries with probable compact companions

TL;DR

This paper refines the identification of Gaia DR3 astrometric binaries with probable compact companions, resulting in a cleaner sample that includes potential black-hole systems and insights into white-dwarf and neutron-star binaries.

Contribution

It provides a more careful analysis and a refined sample of binaries with probable compact companions, improving upon the initial Gaia DR3 triage approach.

Findings

Identified 177 systems with highly probable non-luminous massive companions.

Included 8 candidates potentially hosting black holes with masses > 2.4 M_sun.

Suggested a separation between white-dwarf and neutron-star binaries based on eccentricity and mass.

Abstract

In preparation for the release of the astrometric orbits of Gaia, Shahaf et al. (2019) proposed a triage technique to identify astrometric binaries with compact companions based on their astrometric semi-major axis, parallax, and primary mass. The technique requires the knowledge of the appropriate mass-luminosity relation to rule out single or close-binary main-sequence companions. The recent publication of the Gaia DR3 astrometric orbits used a schematic version of this approach, identifying 735 astrometric binaries that might have compact companions. In this communication, we return to the triage of the DR3 astrometric binaries with more careful analysis, estimating the probability for its astrometric secondary to be a compact object or a main-sequence close binary. We compile a sample of 177 systems with highly-probable non-luminous massive companions, which is smaller but cleaner than the sample reported in Gaia DR3. The new sample includes 8 candidates to be black-hole systems with compact-object masses larger than 2.4 $M_\odot$. The orbital-eccentricity$-$secondary-mass diagram of the other 169 systems suggests a tentative separation between the white-dwarf and the neutron-star binaries. Most white-dwarf binaries are characterized by small eccentricities of about 0.1 and masses of 0.6 $M_\odot$, while the neutron star binaries display typical eccentricities of 0.4 and masses of 1.3 $M_\odot$.