## Abstract

We investigate the consequences of the collapse-induced radiation anticipated before formation of the event horizon. After reviewing the principles underlying semi-classical analysis of black holes we illustrate them by modelling collapse of evaporating massive thin dust shells using two families of metrics for the exterior geometry: the outgoing Vaidya metric and the retarded Schwarzschild metric. We describe how hypothetical pre-Hawking radiation modifies the equation of motion for the shell. Provided that a non-zero radiation flux is perceived by a distant observer, the shell never gets closer than a certain sub-Planckian distance from the Schwarzschild radius. This distance depends only on the shell's mass and evaporation rate. The stress-energy tensor is everywhere finite, but a comoving observer encounters firewall-like energy density and flux. We emphasize the logical connections between different assumptions within the semi-classical approach and discuss consequences of the apparent contradictions between them.

Original language | English |
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Article number | 185005 |

Pages (from-to) | 1-25 |

Number of pages | 25 |

Journal | Classical and Quantum Gravity |

Volume | 35 |

Issue number | 18 |

DOIs | |

Publication status | Published - 17 Aug 2018 |

## Keywords

- thin shells
- pre-Hawking radiation
- collapse