title: Mass of a black hole firewall.
abstract: Quantum entanglement of Hawking radiation has been supposed to give rise to a Planck density "firewall" near the event horizon of old black holes. We show that Planck density firewalls are excluded by Einstein's equations for black holes of mass exceeding the Planck mass. We find an upper limit of 1/(8πM) to the surface density of a firewall in a Schwarzschild black hole of mass M, translating for astrophysical black holes into a firewall density smaller than the Planck density by more than 30 orders of magnitude. A strict upper limit on the firewall density is given by the Planck density times the ratio M(Pl)/(8πM).
authors.affiliation: Copernicus Astronomical Center, ul. Bartycka 18, 00-716 Warszawa, Poland and Department of Physics, University of Gothenburg, SE-412-96 Göteborg, Sweden.
authors.forename: M A
authors.initials: MA
authors.lastname: Abramowicz
authors.affiliation: Copernicus Astronomical Center, ul. Bartycka 18, 00-716 Warszawa, Poland.
authors.forename: W
authors.initials: W
authors.lastname: Kluźniak
authors.affiliation: Copernicus Astronomical Center, ul. Bartycka 18, 00-716 Warszawa, Poland and IAP, UMR 7095 CNRS, UPMC Université Paris 06, 98bis Boulevard Arago, 75014 Paris, France and Astronomical Observatory, Jagiellonian University, ul. Orla 171, 30-244 Kraków, Poland.
authors.forename: J-P
authors.initials: JP
authors.lastname: Lasota