Abstract

Before gravitational-wave astronomy, we knew of a handful of stellar-mass black holes: those observable in X-ray emission as they accrete from a companion. Since the first gravitational wave was detected in 2015, the number of known black holes has rapidly increased. Binary black holes, observed via their gravitational wave emission as they inspiral and merge, now dominate the stellar graveyard. Black holes observed in gravitational waves are typically more massive than those in X-ray binaries, which begs the question: do gravitational waves and X-rays probe different populations of black holes? And if so, how do each of these populations form? In this talk, I will discuss recent work aiming to unearth and distinguish the varying biographies of the stellar graveyard. I will present new results that hint at the formation channels of both X-ray and gravitational-wave sources. I will also explain how the lifetime of a binary black hole can be encoded in its gravitational-wave signal, particularly the signatures of its orbital eccentricity, and address issues in translating these hidden messages.