Institute for Advanced Study / Princeton University Joint Astrophysics Colloquium

Black holes are detected through a variety of methods, each revealing a different part of their nature. These include gravitational-wave emissions that detect compact-object binary mergers, X-ray radiation that captures dramatic accretion episodes in black hole binaries, and astrometry, which measures the dance of a star around an unseen companion. Despite significant progress over the past decade, we still lack a unified framework that connects these seemingly disparate populations. In this talk, I will explore how stellar triples may provide such a connection. I will discuss the role of tertiary companions in driving black hole mergers detectable by LIGO–Virgo–KAGRA, in shaping the formation of accreting X-ray binaries, and in leaving behind wide black hole–stellar systems like those now revealed by Gaia. I will show how the aftermath of a black hole merger in the presence of a tertiary companion can produce rare but detectable electromagnetic counterparts, and how this channel may account for a significant fraction of observed black hole binaries. In short, triples may open the door to linking gravitational-wave events with electromagnetic counterparts and galactic black holes, offering a new way to piece together the life stories of black holes.