Detecting Detached Black Hole binaries through Photometric Variability

TL;DR

This paper investigates the potential to detect detached black hole binaries with luminous companions through photometric variability using Gaia and TESS, predicting hundreds of such systems could be identified in the Milky Way.

Contribution

It introduces a method to identify detached BH-LC binaries via photometric variations and provides population estimates for their detectability with current space missions.

Findings

Gaia can resolve 300-1,000 detached BH-LC binaries with SNR>10.

TESS can resolve approximately 50-200 such binaries.

About 136 binaries are expected to be detectable by both Gaia and TESS.

Abstract

Understanding the connection between the properties of black holes (BHs) and their progenitors is interesting in many branches of astrophysics. Discovering BHs in detached orbits with luminous companions (LCs) promises to help create this map since the LC and BH progenitor are expected to have the same metallicity and formation time. We explore the possibility of detecting BH-LC binaries in detached orbits using photometric variations of the LC flux, induced by tidal ellipsoidal variation, relativistic beaming, and self-lensing. We create realistic present-day populations of detached BH-LC binaries in the Milky Way (MW) using binary population synthesis where we adopt observationally motivated initial stellar and binary properties, star formation history and present-day distribution of these sources in the MW based on detailed cosmological simulations. We test detectability of these sources via photometric variability by Gaia and TESS missions by incorporating their respective detailed detection biases as well as interstellar extinction. We find that Gaia is expected to resolve 300--1,000 (700--1,500) detached BH--LC binaries with SNR>10 (1) depending on the photometric precision and details of supernova physics. Similarly, the number of resolved BH--LC binaries with TESS are ~50--200 (140--350). We find that 136^{+15}_{-15} BH--LC binaries would be common between Gaia and TESS. Moreover, between ~60--70 (50--200) BH--LC binaries identifiable using photometry with SNR >10 may also be resolved using Gaia's radial velocity (astrometry).