Testing the Nature of Dark Compact Objects with Gravitational Waves

Gravitational multipole moments for asymptotically de Sitter spacetimes

“…The study of multipole moments in various contexts has become even more timely, since the discovery of gravitational waves [1][2][3][4][5][6][7]. As we can correctly guess, the observation of gravitational waves from coalescence of binary compact objects can have potential applications in order to address questions about the nature of compact objects, such as black holes, neutron stars and the binary systems thereof [8][9][10][11][12][13][14]. Future space-based gravitational wave detectors, besides mass and spin, will be also able to measure the quadrupole mass moment of the supermassive object with great accuracy [9,15,16], together with higher order multipole moments [17].…”

Modave Lectures on Horizon-Size Microstructure, Fuzzballs and Observations

“…Such a compact object need not be a fuzzball, but should be approximately the same "size" as the black hole -this means it "mimics" the black hole far away from the horizon scale, and only deviates from the black hole geometry approximately at the horizon scale. Such objects are typically referred to as exotic compact objects or ECOs [83,84,75,85]. Their "compactness" can be parametrized by a dimensionless parameter :…”

“…Solution to Exercise 4: Scaling solution. I will choose to work with the five-dimensional metric (66); an alternative would be to work with the four-dimensional metric (85), since these solutions are asymptotically four-dimensional (R 3,1 × S 1 ).…”

Real-Time Holography and Hybrid WKB for BTZ Wormholes

“…The appearance of echoes is a standard feature of many models that introduce structure at the horizon scale, and are a focus for potential experimental explorations of black hole microstates and other horizon-scale compact objects (often called ECOs) [26,27,28,29]. Note, however, that at the moment there has been no conclusive evidence of echoes appearing in current observations [30,31,32,33,34,35,36,37,38,39,40,41,26].…”

“…The appearance of echoes is a standard feature of many models that introduce structure at the horizon scale, and are a focus for potential experimental explorations of black hole microstates and other horizon-scale compact objects (often called ECOs) [26,27,28,29]. Note, however, that at the moment there has been no conclusive evidence of echoes appearing in current observations [30,31,32,33,34,35,36,37,38,39,40,41,26]. It is also unclear whether one would expect echoes to appear in a typical state; as argued in our previous work [42], a typical superposition state of many coherent heavy states would presumably lead to the exponential suppression of any echo structure in the correlator.…”