Spinning Black Holes as Particle Accelerators
TL;DR: The mechanism for particles falling freely from rest at infinity outside a Kerr black hole can in principle collide with an arbitrarily high center of mass energy in the limiting case of maximal black hole spin is elucidated.
Abstract: It has recently been pointed out that particles falling freely from rest at infinity outside a Kerr black hole can in principle collide with an arbitrarily high center of mass energy in the limiting case of maximal black hole spin. Here we aim to elucidate the mechanism for this fascinating result, and to point out its practical limitations, which imply that ultraenergetic collisions cannot occur near black holes in nature.
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TL;DR: In this article, the authors discuss the emerging astrophysical and observational perspectives and implications of the final fate of collapse of a massive matter cloud in gravitation theory, especially on naked singularities which are hypothetical astrophysical objects and on the nature of cosmic censorship hypothesis.
Abstract: It is now known that when a massive star collapses under the force of its own gravity, the final fate of such a continual gravitational collapse will be either a black hole or a naked singularity under a wide variety of physically reasonable circumstances within the framework of general theory of relativity. The research of recent years has provided considerable clarity and insight on stellar collapse, black holes and the nature and structure of spacetime singularities. We discuss several of these developments here. There are also important fundamental questions that remain unanswered on the final fate of collapse of a massive matter cloud in gravitation theory, especially on naked singularities which are hypothetical astrophysical objects and on the nature of cosmic censorship hypothesis. These issues have key implications for our understanding on black hole physics today, its astrophysical applications, and for certain basic questions in cosmology and possible quantum theories of gravity. We consider these issues here and summarize recent results and current progress in these directions. The emerging astrophysical and observational perspectives and implications are discussed, with particular reference to the properties of accretion disks around black holes and naked singularities, which may provide characteristic signatures and could help distinguish these objects.
212 citations
TL;DR: In this paper, the authors studied the collision of two particles in the vicinity of a horizon of a weakly magnetized nonrotating black hole and showed that the maximal collision energy can be high in the limit of a strong magnetic field.
Abstract: We study the collision of particles in the vicinity of a horizon of a weakly magnetized nonrotating black hole. In the presence of the magnetic field innermost stable circular orbits of charged particles can be located close to the horizon. We demonstrate that for a collision of two particles, one of which is charged and revolving at innermost stable circular orbits and the other is neutral and falling from infinity, the maximal collision energy can be high in the limit of a strong magnetic field. This effect has some similarity with the recently discussed effect of high center-of-mass energy for the collision of particles in extremely rotating black holes. We also demonstrate that for ``realistic'' astrophysical black holes their ability to play the role of ``accelerators'' is in fact quite restricted.
140 citations
Cites background from "Spinning Black Holes as Particle Ac..."
...There exist several processes which suppress the possible high value of the collision energy [14, 15]....
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...Let us remind that for near extremal rotating black holes the maximal collision energy per unit mass for particles close the horizon is (cf [14], Eq....
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TL;DR: In this article, the authors derived a general formula for the center-of-mass energy for the near-horizon collision of two particles of the same rest mass on the equatorial plane around a Kerr black hole, and applied this formula to a particle which plunges from the innermost stable circular orbit (ISCO) and collides with another particle near the horizon.
Abstract: We derive a general formula for the center-of-mass (CM) energy for the near-horizon collision of two particles of the same rest mass on the equatorial plane around a Kerr black hole. We then apply this formula to a particle which plunges from the innermost stable circular orbit (ISCO) and collides with another particle near the horizon. It is found that the maximum value of the CM energy ${E}_{\mathrm{cm}}$ is given by ${E}_{\mathrm{cm}}/(2{m}_{0})\ensuremath{\simeq}1.40/\sqrt[4]{1\ensuremath{-}{a}_{*}^{2}}$ for a nearly maximally rotating black hole, where ${m}_{0}$ is the rest mass of each particle and ${a}_{*}$ is the nondimensional Kerr parameter. This coincides with the known upper bound for a particle which begins at rest at infinity within a factor of 2. Moreover, we also consider the collision of a particle orbiting the ISCO with another particle on the ISCO and find that the maximum CM energy is then given by ${E}_{\mathrm{cm}}/(2{m}_{0})\ensuremath{\simeq}1.77/\sqrt[6]{1\ensuremath{-}{a}_{*}^{2}}$. In view of the astrophysical significance of the ISCO, this result implies that particles can collide around a rotating black hole with an arbitrarily high CM energy without any artificial fine-tuning in an astrophysical context if we can take the maximal limit of the black hole spin or ${a}_{*}\ensuremath{\rightarrow}1$. On the other hand, even if we take Thorne's bound on the spin parameter into account, highly or moderately relativistic collisions are expected to occur quite naturally, for ${E}_{\mathrm{cm}}/(2{m}_{0})$ takes 6.95 (maximum) and 3.86 (generic) near the horizon and 4.11 (maximum) and 2.43 (generic) on the ISCO for ${a}_{*}=0.998$. This implies that high-velocity collisions of compact objects are naturally expected around a rapidly rotating supermassive black hole. Implications to accretion flows onto a rapidly rotating black hole are also discussed.
133 citations
TL;DR: The final fate of a massive star collapsing under the force of its own gravity is either a black hole or a naked singularity under a wide variety of physically reasonable circumstances within the framework of general theory of relativity.
Abstract: It is now known that when a massive star collapses under the force of its own gravity, the final fate of such a continual gravitational collapse will be either a black hole or a naked singularity under a wide variety of physically reasonable circumstances within the framework of general theory of relativity. The research of recent years has provided considerable clarity and insight on stellar collapse, black holes and the nature and structure of spacetime singularities. We discuss several of these developments here. There are also important fundamental questions that remain unanswered on the final fate of collapse of a massive matter cloud in gravitation theory, especially on naked singularities which are hypothetical astrophysical objects and on the nature of cosmic censorship hypothesis. These issues have key implications for our understanding on black hole physics today, its astrophysical applications, and for certain basic questions in cosmology and possible quantum theories of gravity. We consider these issues here and summarize recent results and current progress in these directions. The emerging astrophysical and observational perspectives and implications are dicussed, with particular reference to the properties of accretion discs around black holes and naked singularities, which may provide characteristic signatures and could help distinguish these objects.
127 citations
TL;DR: In this article, it has been argued that the similar effect exists for a nonrotating but charged black hole even for the simplest case of radial motion of particles in the Reissner-Nordstrom background.
Abstract: Recently, in the series of works a new effect of acceleration of particles by black holes has been found. Under certain conditions, the energy in the center-of-mass system can become infinitely large. The essential ingredient of such effect is the rotation of a black hole. In this work, it has been argued that the similar effect exists for a nonrotating but charged black hole even for the simplest case of radial motion of particles in the Reissner-Nordstrom background. All main features of the effect under discussion due to rotating black holes have their counterpart for the nonrotating charged ones.
125 citations
References
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01 Jan 2012
139,059 citations
"Spinning Black Holes as Particle Ac..." refers background in this paper
...Note added in proof: The possibility of ultrahigh energy collisions catalyzed by a rotating black hole was noticed long ago, in the context of the study of collisional Penrose processes [7, 8]....
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1,100 citations
TL;DR: It is shown that intermediate mass black holes conjectured to be the early precursors of supermassive black holes and surrounded by relic cold dark matter density spikes can act as particle accelerators with collisions, in principle, at arbitrarily high center-of-mass energies in the case of Kerr black holes.
Abstract: We show that intermediate mass black holes conjectured to be the early precursors of supermassive black holes and surrounded by relic cold dark matter density spikes can act as particle accelerators with collisions, in principle, at arbitrarily high center-of-mass energies in the case of Kerr black holes. While the ejecta from such interactions will be highly redshifted, we may anticipate the possibility of a unique probe of Planck-scale physics.
470 citations
TL;DR: In this article, the authors consider a subset of the physical processes that determine the spin j ≡ a/M of astrophysical black holes, and they show that, at least for one sequence of flow models, spin equilibrium is reached for j ~ 0.9.
Abstract: We consider a subset of the physical processes that determine the spin j ≡ a/M of astrophysical black holes. These include (1) Initial conditions. Recent models suggest that the collapse of a supermassive star is likely to produce a black hole with j ~ 0.7. (2) Major mergers. The outcome of a nearly equal mass black hole-black hole merger is not yet known, but we review the current best guesses and analytic bounds. (3) Minor mergers. We recover the result of Blandford & Hughes that accretion of small companions with isotropically distributed orbital angular momenta results in spin-down, with j ~ M-7/3. (4) Accretion. We present new results from fully relativistic magnetohydrodynamic (MHD) accretion simulations. These show that, at least for one sequence of flow models, spin equilibrium (dj/dt = 0) is reached for j ~ 0.9, far less than the canonical value 0.998 of Thorne that was derived in the absence of MHD effects. This equilibrium value may be inapplicable to some accretion flows, particularly thin disks. Nevertheless, it opens the possibility that black holes that have grown primarily through accretion are not maximally rotating.
301 citations