We argue that the possibility of having infinite energy in the centre of mass frame of colliding particles is a generic property of rotating black holes. We suggest a general model-independent derivation valid for dirty black holes. The earlier observations for the Kerr or Kerr-Newman metrics are confirmed and generalized.
Recently, in the series of works a new effect of acceleration of particles by black holes was found. Under certain conditions, the energy in the centre of mass frame can become infinitely large. The essential ingredient of such effect is the rotation of a black hole. In the present Letter, we argue 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-Nordström background. All main features of the effect under discussion due to rotating black holes have their counterpart for the nonrotating charged ones. PACS numbers: 04.70.Bw, 97.60.Lf, 04.40.Nr
I. INTRODUCTIONRecently, it was made an interesting observation that black holes can accelerate particles up to unlimited energies E cm in the centre of mass frame [1]. This stimulated further works in which details of this process were investigated [2] -[6] and, in particular was found that the effect is present not only for extremal black holes but also for nonextremal ones [2]. These results have been obtained for the Kerr metric (they were also extended to the extremal Kerr-Newman one [3] and the stringy black hole [4]). In the work [7] generalization of these observations was performed and it was demonstrated that the effect in question exists in a generic black hole background (so a black hole can be surrounded by matter) provided a black hole is rotating. Thus, rotation seemed to be an essential part of the effect. It is also necessary that one of colliding particles have the angular momentumwhere E is the energy, ω H is the angular velocity of a generic rotating black hole. If ω H → 0, L 1 → ∞, * Electronic address: zaslav@ukr.net
Objects that are on the verge of being extremal black holes but actually are distinct in many ways are called quasi-black holes. Quasi-black holes are defined here and treated in a unified way through the displaying of their properties. The main ones are (i) there are infinite redshift whole regions, (ii) the spacetimes exhibit degenerate, almost singular, features but their curvature invariants remain perfectly regular everywhere, (iii) in the limit under discussion, outer and inner regions become mutually impenetrable and disjoint, although, in contrast to the usual black holes, this separation is of a dynamical nature, rather than purely causal, (iv) for external far away observers the spacetime is virtually indistinguishable from that of extremal black holes. It is shown, in addition, that quasi-black holes must be extremal. Connections with black hole and wormhole physics are also drawn.
Nonextreme black hole in a cavity can achieve the extreme state with a zero surface gravity at a finite temperature on a boundary, the proper distance between the boundary and the horizon being finite. The classical geometry in this state is found explicitly for four-dimensional spherically-symmetrical and 2 + 1 rotating holes. In the first case the limiting geometry depends only on one scale factor and the whole Euclidean manifold is described by the Bertotti-Robinson spacetime. The general structure of a metric in the limit under consideration is also found with quantum corrections taken into account. Its angular part represents a two-sphere of a constant radius. In all cases the Lorentzian counterparts of the metrics are free from singularities.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.