Echoes from corpuscular black holes

Abstract

In the corpuscular picture of black hole there exists no geometric notion of horizon which, instead, only emerges in the semi-classical limit. Therefore, it is very natural to ask -what happens if we send a signal towards a corpuscular black hole? We show that quantum effects at the horizon scale imply the existence of a surface located at an effective radius R = Rs(1 + ) slightly larger than the Schwarzschild radius Rs, where = 1/N and N is the number of gravitons composing the system. Consequently, the reflectivity of the object can be non-zero and, indeed, we find that incoming waves with energies comparable to the Hawking temperature can have a probability of backscattering of order one. Thus, modes can be trapped between the two potential barriers located at the photon sphere and at the surface of a corpuscular black hole, and periodic echoes can be produced. The time delay of echoes turns out to be of the same order of the scrambling time, i.e., in units of Planck length it reads √ N log N. We also show that the -parameter, or in other words the compactness, of a corpuscular black hole coincides with the quantum coupling that measures the interaction strength among gravitons, and discuss the physical implications of this remarkable feature.

How does a dark compact object ringdown?

“…The time delay between echoes depends on the compactness of the object, whereas the relative amplitude between subsequent echoes is related to the reflectivity. Considerable attention has been devoted to the study of this signal in a variety of models of near-horizon quantum structures [42][43][44][45][46][47][48] in the context of exotic compact objects in general relativity [49,50], and for modified-gravity scenarios [28,[51][52][53]. Phenomenological waveform models have also been analyzed in detail [39,[54][55][56][57][58][59][60][61] and implemented in actual searches in LIGO/Virgo data [41,42,59,[62][63][64][65][66][67] (see Refs.…”

How does a dark compact object ringdown?

“…The time delay between echoes depends on the compactness of the object, whereas the relative amplitude between subsequent echoes is related to the reflectivity. Considerable attention has been devoted to the study of this signal in a variety of models of near-horizon quantum structures [41][42][43][44][45][46], in the context of exotic compact objects in General Relativity [47,48], and for modifiedgravity scenarios [28,[49][50][51]. Phenomenological waveform models have also been analyzed in detail [38,[52][53][54][55][56][57][58][59] and implemented in actual searches in LIGO/Virgo data [40,41,57,[60][61][62][63][64][65] (see Refs.…”

Tidal response and near-horizon boundary conditions for spinning exotic compact objects

“…Alternatively, a stronger probe of the reflectivity is provided by waves that propagate toward the horizon of the final (remnant) black hole after the merger of two black holes -in the form of repeated GW echoes at late times in the ringdown signal of a binary merger event [28][29][30][31][32][33][34][35][36][37]. Following this line of thought, the gravitational echoes has been extensively studied in different models of near-horizon structures [38][39][40][41][42][43]. Even though the idea of ECOs might be speculative, one can always regard the search for ECOs as one to quantify the darkness of the final objects in binary merger events, and in this way its importance cannot be overstated.…”