Abstract:
Conventional wisdom has it that the masses of stellar black holes are
bounded below and above by gaps. The hypothesised low-mass gap,
between ∼2.5 − 5 solar masses, is a prediction of supernovae
physics. This gap separates neutron stars from the lightest black
holes observed in Galactic X-ray binaries. The high-mass gap, between
∼50 − 120 solar masses, is predicted to occur due to the onset of
pair-instability supernovae, which disrupt the stars that would
otherwise populate this range of masses. However, recent results from
the LIGO-Virgo Collaborations hint that reality is more
complicated. The detection of GW190814, sourced from the coalescence
of a 23 solar mass black hole with a 2.6 solar mass compact object,
illustrates that compact objects exist in the purported low-mass
gap. Meanwhile, claims of an electromagnetic counterpart to the binary
black hole merger S190521g hint at > 75 solar mass black holes in the
high-mass gap. In this talk, I review what we have learned about black
holes from gravitational-wave astronomy, I discuss some of the
challenges understanding the origin of GW190814, and I highlight how
upcoming LIGO-Virgo results will shed new light on the properties of
compact binaries. (Image credit: Carl Knox, OzGrav)
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