When Black Holes Can Wear Pants
Abstract
We investigate the conditions under which black hole fragmentation, the splitting of a black hole horizon into multiple smaller ones, may occur. The simplest realization is that of a single black hole horizon splitting into two, giving rise to the eponymous pants topology. In classical general relativity, the Bekenstein-Hawking area law forbids such processes for Schwarzschild black holes. For spinning Kerr black holes, purely kinematic analyses impose constraints that prevent fragmentation, even in regimes where entropy considerations might allow it, except possibly in near-extremal cases. We then hunt for scenarios where black holes can wear pants: from the well-known Gregory-Laflamme instability in higher dimensions, to the potential effect of superradiant instabilities in non-axisymmetric radiation trapping, to finally gravitational models that modify the relations between entropy and/or horizon radius and the black hole mass in four dimensions. In all such cases, emission of small fragments can be entropically favored, however its occurrence still depends on the kinematic configuration of the initial state. Our analysis clarifies the theoretical landscape where black holes may fragment, which is particularly relevant for primordial black holes and catastrophic events such as black hole mergers.
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BibTeX
@misc{cacciapaglia2026when,
title = {{When Black Holes Can Wear Pants}},
author = {Giacomo Cacciapaglia and Manuel Del Piano and Francesco Sannino and Vania Vellucci},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2606.24642},
eprint = {2606.24642},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.24642},
note = {CC BY-SA 4.0},
}
RIS
TY - UNPB
TI - When Black Holes Can Wear Pants
AU - Giacomo Cacciapaglia
AU - Manuel Del Piano
AU - Francesco Sannino
AU - Vania Vellucci
PY - 2026
DA - 2026/09/26
PB - arXiv
DO - 10.48550/arxiv.2606.24642
UR - https://arxiv.org/abs/2606.24642
AB - We investigate the conditions under which black hole fragmentation, the splitting of a black hole horizon into multiple smaller ones, may occur. The simplest realization is that of a single black hole horizon splitting into two, giving rise to the eponymous pants topology. In classical general relativity, the Bekenstein-Hawking area law forbids such processes for Schwarzschild black holes. For spinning Kerr black holes, purely kinematic analyses impose constraints that prevent fragmentation, even in regimes where entropy considerations might allow it, except possibly in near-extremal cases. We then hunt for scenarios where black holes can wear pants: from the well-known Gregory-Laflamme instability in higher dimensions, to the potential effect of superradiant instabilities in non-axisymmetric radiation trapping, to finally gravitational models that modify the relations between entropy and/or horizon radius and the black hole mass in four dimensions. In all such cases, emission of small fragments can be entropically favored, however its occurrence still depends on the kinematic configuration of the initial state. Our analysis clarifies the theoretical landscape where black holes may fragment, which is particularly relevant for primordial black holes and catastrophic events such as black hole mergers.
ER -