New Compact Object Binary Populations with Precision Astrometry (Roman White Paper)

TL;DR

This paper discusses how the Roman Space Telescope's advanced astrometric capabilities can significantly improve the detection and study of compact object binaries, especially wide-orbit black hole systems, beyond Gaia's current limits.

Contribution

It proposes using Roman's microlensing survey to identify new wide-orbit black hole binaries and expand understanding of their population and distribution.

Findings

Roman can detect binaries several magnitudes deeper than Gaia.

Potential to discover numerous previously unknown black hole binaries.

Enhanced understanding of binary evolution and black hole formation.

Abstract

Compact object binaries (a black hole or a neutron star orbiting a non-degenerate stellar companion) are key to our understanding of late massive star evolution, in addition to being some of the best probes of extreme gravity and accretion physics. Gaia has opened the door to astrometric studies of these systems, enabling geometric distance measurements, kinematic estimation, and the ability to find new previously unknown systems through measurement of binary orbital elements. Particularly puzzling are newly found massive black holes in wide orbits (~AU or more) whose evolutionary history is difficult to explain. Astrometric identification of such binaries is challenging for Gaia, with only two such examples currently known. Roman's enormous grasp, superb sensitivity, sharp PSF and controlled survey strategy can prove to be a game-changer in this field, extending astrometric studies of compact object binaries several mag deeper than Gaia. We propose to use the microlensing Galactic Bulge Time Domain Survey to identify new wide-orbit black hole compact object binaries, determine their prevalence and their spatial distribution, thus opening up new parameter space in binary population studies.