Distinguishing fuzzballs from black holes through their multipolar structure. (arXiv:2007.01743v1 [hep-th])
<a href="http://arxiv.org/find/hep-th/1/au:+Bianchi_M/0/1/0/all/0/1">Massimo Bianchi</a>, <a href="http://arxiv.org/find/hep-th/1/au:+Consoli_D/0/1/0/all/0/1">Dario Consoli</a>, <a href="http://arxiv.org/find/hep-th/1/au:+Grillo_A/0/1/0/all/0/1">Alfredo Grillo</a>, <a href="http://arxiv.org/find/hep-th/1/au:+Morales_J/0/1/0/all/0/1">Jos&#xe8; Francisco Morales</a>, <a href="http://arxiv.org/find/hep-th/1/au:+Pani_P/0/1/0/all/0/1">Paolo Pani</a>, <a href="http://arxiv.org/find/hep-th/1/au:+Raposo_G/0/1/0/all/0/1">Guilherme Raposo</a>

Within General Relativity, the unique stationary solution of an isolated
black hole is the Kerr spacetime, which has a peculiar multipolar structure
depending only on its mass and spin. We develop a general method to extract the
multipole moments of arbitrary stationary spacetimes and apply it to a large
family of horizonless microstate geometries. The latter can break the axial and
equatorial symmetry of the Kerr metric and have a much richer multipolar
structure, which provides a portal to constrain fuzzball models
phenomenologically. We find numerical evidence that all multipole moments are
always larger (in absolute value) than those of a Kerr black hole with the same
mass and spin. Current measurements of the quadrupole moment of black-hole
candidates could place only mild constraints on fuzzballs, while future
gravitational-wave detections of extreme mass-ratio inspirals with the space
mission LISA will improve these bounds by orders of magnitude.

Within General Relativity, the unique stationary solution of an isolated
black hole is the Kerr spacetime, which has a peculiar multipolar structure
depending only on its mass and spin. We develop a general method to extract the
multipole moments of arbitrary stationary spacetimes and apply it to a large
family of horizonless microstate geometries. The latter can break the axial and
equatorial symmetry of the Kerr metric and have a much richer multipolar
structure, which provides a portal to constrain fuzzball models
phenomenologically. We find numerical evidence that all multipole moments are
always larger (in absolute value) than those of a Kerr black hole with the same
mass and spin. Current measurements of the quadrupole moment of black-hole
candidates could place only mild constraints on fuzzballs, while future
gravitational-wave detections of extreme mass-ratio inspirals with the space
mission LISA will improve these bounds by orders of magnitude.

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