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Nonlinear evolution of the ergoregion instability: Turbulence, bursts of radiation, and black hole formation

Nils Siemonsen1,2,* and William E. East3,†

  • *Contact author: nils.siemonsen@princeton.edu
  • †Contact author: weast@perimeterinstitute.ca
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Phys. Rev. D 114, 064022 – Published 8 September, 2026

DOI: https://doi.org/10.1103/2jnw-68dm

Abstract

Spacetimes with an ergoregion that is not connected to a horizon are linearly unstable. While the linear regime has been studied in a number of settings, little is known about the nonlinear evolution of this ergoregion instability. Here, we investigate this by numerically evolving the unstable growth of a massless vector field in a rapidly spinning boson star in full general relativity. We find that the backreaction of the instability causes the star to become more gravitationally bound, accelerating the growth, and eventually leading to black hole formation. During the nonlinear growth phase, small scale features develop in the unstable mode and emit radiation as nonlinear gravitational interactions mediate a direct turbulent cascade. The gravitational wave signal exhibits bursts, akin to so-called gravitational wave echoes, with increasing amplitude towards black hole formation.

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Phys. Rev. D 114, 064022– Published 8 September, 2026
  • Received 23 December 2025
  • Accepted 21 July 2026
Article part of CHORUS
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