Abstract
We construct a family of non-supersymmetric extremal black holes and their horizonless microstate geometries in four dimensions. The black holes can have finite angular momentum and an arbitrary charge-to-mass ratio, unlike their supersymmetric cousins. These features make them and their microstate geometries astrophysically relevant. Thus, they provide interesting prototypes to study deviations from Kerr solutions caused by new horizon-scale physics. In this paper, we compute the gravitational multipole structure of these solutions and compare them to Kerr black holes. The multipoles of the black hole differ significantly from Kerr as they depend non-trivially on the charge-to-mass ratio. The horizonless microstate geometries (that are comparable in size to a black hole) have a similar multipole structure as their corresponding black hole, with deviations to the black hole multipole values set by the scale of their microstructure.
Highlights
The observation of gravitational waves by the LIGO collaboration [1] from colliding black holes has lead to a paradigm shift in how we think about black holes: they are physical objects that can be observed and studied in nature
Their theoretical studies have led to many interesting puzzles and paradoxes which have offered important windows into quantum gravity; chief among them are the origin of the microstates that make up the Bekenstein-Hawking entropy, and the unitary problem of black hole evaporation
We show that the deviations are rather “random” as they depend on the geometry of the topologically non-trivial bubbles that give the horizon-scale structure, and they can be either positive or negative; this is in contrast with the analysis of [17], where the multipoles of certain microstate geometries were found to be larger than the multipoles of their corresponding black holes
Summary
The observation of gravitational waves by the LIGO collaboration [1] from colliding black holes has lead to a paradigm shift in how we think about black holes: they are physical objects that can be observed and studied in nature. An important class of observables that can distinguish microstate geometries with horizon-size structure from classical GR black holes is the tower of gravitational multipole moments These observables are already astrophysically interesting and will become more so in the era of gravitational-wave astronomy. This initial analysis will provide the baseline to study deviations of multipoles caused by horizon-scale microstructure in the almost-BPS microstate geometries when compared to the almost-BPS black holes and to the Kerr black holes Another benefit of studying almost-BPS solutions is to contrast them with the phenomenological modeling of Exotic Compact Objects (ECOs) [20,21,22]. Multipoles of almost-BPS microstate geometries have a highly non-trivial dependence on the internal degrees of freedom of the geometry These deviate from the multipoles of the almost-BPS black hole at the same scale as the size of the microstructure in the near horizon region..
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
