XII BLACK HOLES WORKSHOP

Guimarães 19-20^th December 2019

Einstein's theory of general relativity predicts that the only stationary configuration of an isolated black hole is the Kerr spacetime, which has a unique multipolar structure and a spherical shape when non-spinning. This is in striking contrast to the case of neutron stars and models of horizonless ultracompact objects that can have arbitrary multipolar deformations. In this talk we will show we show that the more compact a ultracompact object is, the less hairy it will be. These results suggest that it is challenging (but possibly feasible with next-generation gravitational-wave detectors) to distinguish Kerr black holes from a large class of ultracompact exotic objects on the basis of their different multipolar structure. We will also discuss neutron stars with intrinsic quadrupole moments, which provide a more accurate description for stellar remnants. These new intrinsic deformations are significant for gravitational-wave parameter estimation, for the electromagnetic signal from accreting neutron stars, and for tests of the nature of compact objects.

Oral presentation: yes. Poster: no.