Astronomy Colloquium

Black holes are now detected through a variety of methods, each revealing a different facet of their nature. These include gravitational-wave detectors that observe the mergers of compact binaries, the Gaia mission, which uncovers detached black holes quietly orbiting stellar companions, and X-ray telescopes that capture the dramatic accretion episodes of black hole binaries. However, despite the significant progress of 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 merger in a triple 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.