PIRSA:25080044 Conference Cosmology

DOI10.48660/25080044

Conference/School: Charting the Future Symposium

Siemonsen, N.P. (2025). Ergoregion instability: the nonlinear story. Perimeter Institute. https://pirsa.org/25080044

Siemonsen, Nils Peter. Ergoregion instability: the nonlinear story. Perimeter Institute, Aug. 28, 2025, https://pirsa.org/25080044 

@misc{ pirsa_PIRSA:25080044,
  doi = {10.48660/25080044},
  url = {https://pirsa.org/25080044},
  author = {Siemonsen, Nils Peter},
  keywords = {Cosmology, Particle Physics, Strong Gravity},
  language = {en},
  title = {Ergoregion instability: the nonlinear story},
  publisher = {Perimeter Institute},
  year = {2025},
  month = {aug},
  note = {PIRSA:25080044 see, \url{https://pirsa.org}}
}

Abstract

Compact, spinning, and horizonless spacetimes can develop an ergoregion, where massless negative-energy states are quasi-trapped and drive the ergoregion instability. I will briefly review the linear mechanism and then describe recent progress in understanding the nonlinear evolution. Nonlinear mode coupling can amplify high-frequency modes through a turbulent direct cascade inside the ergoregion. Gravitational backreaction leads to an enhancement of the unstable process, and ultimately, black hole formation. I will illustrate the relevant dynamics and discuss implications for strongly gravitating horizonless systems.

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