It was recently shown that black holes could be bouncing stars as a consequence of quantum gravity. We investigate the astrophysical signals implied by this hypothesis, focusing on primordial black holes. We consider different possible bounce times and study the integrated diffuse emission.
I. THE MODELA new possible window for observing quantum gravitational effects has been recently pointed out in [1] (some details were refined in [2]). The idea is grounded on a result of loop cosmology [3]: when matter or radiation reaches the Planck density, quantum gravity generates a sufficient pressure to counterbalance the classically attractive gravitational force. In a black hole, matter's collapse could stop before the central singularity is formed. The standard event horizon of the black hole can be replaced by an apparent horizon [4] which is locally equivalent to an event horizon, but from which matter can eventually bounce out. The model is not specific to loop quantum gravity (for instance a similar scenario can be realized in asymptotic safety [5]). The case of non-singular black holes has been investigated by many authors [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24].A heuristic description of the model we are studying can be given as follows. When the density of matter becomes high enough, quantum gravity effects generate sufficient pressure to compensate the matter's weight, the collapse ends, and matter bounces out. A collapsing "black hole" might avoid sinking into the r = 0 singularity, as much as an electron in a Coulomb potential does not sink all the way into r = 0 because of quantum mechanical effects. The picture is close to Giddings's remnant scenario [25] but with a macroscopic remnant developing into a white hole.The phenomenology associated with this scenario was considered in [26], opening the fascinating possibility to detect quantum gravity effects far below the Planck energy. It was shown there that primordial black holes (PBHs) could generate a signal in the 100 MeV range, possibly compatible with very fast gamma-ray bursts * Electronic address: aurelien.barrau@cern.ch † Electronic address: boris.bolliet@ens-lyon.fr ‡ Electronic address: fvidotto@science.ru.nl § Electronic address: celinew@kth.se [27]. Observability is made possible by the amplification due to the large ratio of the black hole lifetime over the Planck time [28].The scenario was developed in [29] with the discovery of an explicit metric satisfying Einstein's equations everywhere outside the quantum region. The model describes a quantum tunneling from a classical in-falling black hole to a classical emerging white hole. The process is seen in extreme "slow motion" from the outside because of the huge time dilatation inside the gravitational potential: this is why massive black holes would appear to us as long living black holes. Only light black holes -as primordial black holes-are expected to yield observational signatures of this model because the time required for the bounce to occur can then be sm...