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Cauchy horizon stability and instability of regular black holes

Alfio Bonanno*

Antonio Panassiti†

Frank Saueressig‡

  • High Energy Physics Department, Institute of Mathematics, Astrophysics, and Particle Physics, Radboud University, Heyendalseweg 135, 6525 AJ Nijmegen, The Netherlands

  • *Contact author: alfio.bonanno@inaf.it
  • †Contact author: antonio.panassiti@phd.unict.it
  • ‡Contact author: f.saueressig@science.ru.nl
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Phys. Rev. D 114, 064027 – Published 8 September, 2026

DOI: https://doi.org/10.1103/34w6-s2yl

Abstract

A common feature of regular black-hole spacetimes is the presence of an inner Cauchy horizon. The analogy to the Reissner-Nordström solution then suggests that these geometries suffer from a mass-inflation effect, rendering the Cauchy horizon unstable. Recently, it was shown that this analogy fails for certain classes of regular black holes, including the Hayward solution, where the late-time behavior of the mass function no longer grows exponentially but follows a power law. In this work, we extend these results in a twofold way. First, we determine the basin of attraction for the power-law attractor, showing that the tamed growth of the mass function is generic. Second, we extend the systematic analysis to the Bardeen and Dymnikova geometries, the Ghosh-Culetu black hole, and a spacetime arising from a nonsingular collapse model newly proposed in the context of asymptotically safe quantum gravity. Remarkably, in the latter solution, the Misner-Sharp mass at the Cauchy horizon remains of the same order of magnitude of the mass of the black hole, since its growth is just logarithmic.

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Outline

Information

Phys. Rev. D 114, 064027– Published 8 September, 2026
  • Received 18 July 2025
  • Accepted 20 July 2026
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