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10th of November 2021
ATNF Colloquium
An Interview with an Intermediate-Mass Black Hole: Gravitational-Wave Signal GW190521
Isobel Romero-Shaw (Monash University/OzGrav)
Abstract: On the 21st of May, 2019, gravitational-wave observatories LIGO and Virgo detected something we had never seen before. The short signal they captured — more of a low-pitched ‘blip’ than a ‘chirp’ — emanated from the creation of an intermediate-mass black hole, making GW190521 the first direct evidence of the existence of such objects. This intermediate-mass black hole was formed from the merger of two smaller black holes, at least one of which had a mass that is troublesome to explain through stellar evolution. Pair-instability supernovae are thought to cause a “gap” in the mass distribution of black holes, such that black holes with masses between 60 and 130 times the mass of the Sun should not exist. The components of GW190521 had masses of about 85 and 65 solar masses — so how did these “forbidden” black holes come into existence? In this talk, I will present the results of the LIGO—Virgo Collaboration’s analysis of GW190521. I will explain how we can learn a lot about the source from such a short signal, and discuss potential formation mechanisms for this mysteriously massive binary. Finally, I will discuss the implications for the population of compact binaries if any of these formation mechanisms are confirmed.

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