Simulating black hole imposters

I briefly describe motivation for, and the current state of research into understanding the structure and dynamics of black hole “imposters”: objects that could be misidentified as Kerr black holes given the current precision of LIGO/Virgo gravitational wave observations, or EHT accretion disk measurements. I use the term “weak imposter” to describe an object which is a black hole, i.e. it has an event horizon, but whose structure and dynamics is governed by a modified gravity theory. At the other end of the spectrum are “strong imposters”: hypothetical horizonless, compact objects conjectured to form instead of black holes during gravitational collapse. To discover or rule-out imposters will require a quantitative understanding of their merger dynamics. This is hampered at present by a dearth of well-posed theoretical frameworks to describe imposters beyond perturbations of Kerr black holes and their general relativistic binary dynamics. That so little is known about non-perturbative modifications to dynamical, strongfield gravity is, I argue, due to a lamppost effect.