Black hole bombs and explosions: from astrophysics to particle physics

TL;DR

The article surveys how dynamical black holes serve as laboratories for both gravity and particle physics, focusing on superradiance, instabilities, and high-energy collisions. It explains energy extraction mechanisms such as the superradiant condition $\omega < m\Omega$ and the formation of black hole bombs, including AdS and astrophysical realizations, and it connects these to massive fields, scalar-tensor theories, and the axiverse. In the collision regime, the work emphasizes the hoop conjecture, the near-adiabatic role of approximation methods, and the extreme-energy behavior that brings BH physics into contact with trans-Planckian questions, all while highlighting open issues in nonlinear dynamics and backreaction. Overall, black holes are portrayed as natural detectors and amplifiers of new physics, with observational and numerical advances set to propel tests of gravity and beyond-Standard-Model phenomena.

Abstract

Black holes are the elementary particles of gravity, the final state of sufficiently massive stars and of energetic collisions. With a forty-year long history, black hole physics is a fully-blossomed field which promises to embrace several branches of theoretical physics. Here I review the main developments in highly dynamical black holes with an emphasis on high energy black hole collisions and probes of particle physics via superradiance. This write-up, rather than being a collection of well known results, is intended to highlight open issues and the most intriguing results.

Figures (10)

• Figure 1: Scheme of the hypothetical chain reaction in a cluster of rotating black holes. The incident arrow denotes an incident wave on the rotating black hole, which is then amplified and exits with larger amplitude, before interacting with other black holes. The super-radiantly scattered wave interacts with other black holes, in an exponential cascade.
• Figure 2: Rotating black hole surrounded by perfectly reflecting cavity. Low-frequency radiation is successively reflected at the mirror and amplified close to the black hole, in an exponential cascade.
• Figure 3: Rotating black hole surrounded by perfectly reflecting cavity. Low-frequency radiation is successively reflected at the mirror and amplified close to the black hole, in an exponential cascade. Taken from Ref. Cardoso:2004nk.
• Figure 4: The dipole amplitude at selected extraction radii $r_{\rm ex}$ for a massive scalar field with $M\mu_S = 0.42$ in a Kerr background with $a=0.99M$. The initial pulse is a gaussian $\Psi_{11}=e^{-(r-12)^2/4}$ and has angular dependence given by $Y_{1-1}-Y_{11}$ with $Y_{lm}$ being the scalar spherical harmonic. The black hole has mass $M=1$. Taken from Ref. Witek:2012tr.
• Figure 5: Contour plots in the black hole Regge plane Arvanitaki:2010sy corresponding to an instability timescale shorter than $\tau_{\rm Hubble}$ (continuous lines) or $\tau_{\rm Salpeter}$ (dashed lines) for different values of the vector field mass $m_v={{\mu}}\hbar$. The experimental points (with error bars) refer to the supermassive black holes listed in Table 2 of Brenneman:2011wz; the rightmost point corresponds to the supermassive black hole in Fairall 9 Schmoll:2009gq. Supermassive black holes lying above each of these curves would be unstable on an observable timescale, and therefore they exclude the corresponding range of Proca field masses. Taken from Refs. Pani:2012bp.