Black hole bombs and explosions: from astrophysics to particle physics

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.Keywords Black holes · Superradiance · Cosmic Censorship · Transplanckian collisions IntroductionThe Kerr-Newman family of black holes in stationary four-dimensional, asymptotically flat spacetimes exhausts all possible electro-vacuum solutions in General Relativity. Theoretical aspects of black hole physics were fully developed decades ago, when the Kerr-Newman family was discovered and characterized. Most of the tools to understand black hole physics have been in place since that period and most processes involving black holes were controlled at the order-of-magnitude level for at least two decades. Perhaps due to these reasons, "black hole physics" conjures up images of horizons and time-warps and old-fashioned, frozen-in-time topics to lay audiences. However, in the last years the activity in the field is bubbling up Vitor Cardoso CENTRA, Departamento de Física, Instituto Superior Técnico, Universidade Técnica de Lisboa -UTL, Av. Rovisco Pais 1, 1049 Lisboa, Portugal E-mail: vitor.cardoso@ist.utl.pt Present address: Perimeter Institute for Theoretical Physics, Waterloo, Ontario N2J 2W9, Canada 2 Vitor Cardoso and the interest in these issues has widened, driven by several unrelated events at the observational/instrumental, technical and conceptual levels such as (i) our capacity to observationally scrutinize the region close to the horizon within a few Schwarzschild radii, with radio and deep infrared interferometry, of which we have seen but the first steps [1,2,3,4];(ii) the ability to measure black hole spins more accurately than ever before using X-ray spectroscopy [5,6] or "continuum-fitting" methods [7]. Measurement of black hole mass and spin is one necessary step in testing General Relativity [8]; (iii) huge technological progress in gravitational-wave observatories, some of which had been gathering data at design sensitivities for several years and are now being upgraded to sensitivities one order of magnitude higher (black hole binaries are thought to be among the first objects to ever be detected in the gravitational-wave spectrum);(iv) our ability to numerically evolve black hole binaries at the full nonlinear level [9,10,11] and its immediate importance for gravitational-wave searches and high-energy physics [12]; (v) improvement of perturbative schemes, either by an understanding of regularization schemes to handle the self-force [13,14], or by faster and more powerful methods to deal with the full ladder of pe...

Exploring New Physics Frontiers Through Numerical Relativity

“…When the BH is rotating, a novel effect can be triggered: superradiance [827, 828, 83, 164]. Superradiance consists of energy extraction from rotating BHs, and a transfer of this energy to the interacting field [164].…”

“…Superradiance consists of energy extraction from rotating BHs, and a transfer of this energy to the interacting field [164]. For a monochromatic wave of frequency ω , the condition for superradiance is [827, 828, 83, 164] where m is the azimuthal harmonic index and Ω H is the angular velocity of the BH horizon.…”

“…Superradiance consists of energy extraction from rotating BHs, and a transfer of this energy to the interacting field [164]. For a monochromatic wave of frequency ω , the condition for superradiance is [827, 828, 83, 164] where m is the azimuthal harmonic index and Ω H is the angular velocity of the BH horizon. If, in addition, the field is massive, a “BH bomb-type” mechanism can ensue [241, 268, 843, 171] leading to an instability of the spacetime and the growth of a scalar condensate outside the BH horizon [605, 815, 794, 280, 588, 164].…”

“…For a monochromatic wave of frequency ω , the condition for superradiance is [827, 828, 83, 164] where m is the azimuthal harmonic index and Ω H is the angular velocity of the BH horizon. If, in addition, the field is massive, a “BH bomb-type” mechanism can ensue [241, 268, 843, 171] leading to an instability of the spacetime and the growth of a scalar condensate outside the BH horizon [605, 815, 794, 280, 588, 164]. The rich phenomenology of scenarios where fundamental fields couple to gravity motivated recent work on the subject, where full nonlinear evolutions are performed [588, 289, 410, 92].…”

“…For this to happen, the object would effectively stall at a superradiant orbit, with a Newtonian frequency Ω = 2 μ s for the dominant quadrupolar emission. These are called floating orbits , and were verified at linearized level [165, 164]. 21 Nonlinear evolutions of systems on floating orbits are extremely challenging on account of all the different extreme scales involved.…”