Ultrahigh-Energy Debris from the Collisional Penrose Process

2015

Mod. Phys. Lett. A

If two particles move toward a black hole and collide near the horizon, the energy E c.m. in the centre of mass can grow unbounded. This is a so-called Bañados-SilkWest (BSW) effect. One of problems creating obstacles to the possibility of its observation consists in that individual energy E of a fragment at infinity remains finite because of redshift. We show that in the case of head-on collision, debris may have unbounded energy E. An essential ingredient of this scenario is a particle moving away from a black hole in the near-horizon region. It can appear due to precedent collision that implies multiple scattering.

Section: Summary and Discussionsupporting

confidence: 74%

“…Quite recently, one more work appeared [10] in which it was claimed that energies E of debris may be not only very large but, in principle, unbound. The results of this paper are presented in the form of figures describing numerical calculations.…”

Section: Introductionmentioning

confidence: 99%

Unbounded energies of debris from head-on particle collisions near black holes

2015

Mod. Phys. Lett. A

“…In what follows, we call this Schnittman process (scenario). Later, numerically [17] and analytically [18] it was found that if colliding particles move in opposite directions and both of them are usual, a formally infinite efficiency becomes possible (so-called super-Penrose process). The problem is, however, that a usual particle with a finite energy cannot move away from a black hole although for the critical particle this is possible ( [10], [13], [14]).…”

Section: Quarks-2016mentioning

confidence: 99%

High energy particle collisions near black holes

2016

EPJ Web Conf.

Abstract. If two geodesic particles collide near a rotating black hole, their energy in the centre of mass frame E c.m. can become unbound under certain conditions (the so-called BSW effect). The special role is played here by so-called critical geodesics when one of particles has fine-tuned energy and angular momentum. The nature of geodesics reveals itself also in fate of the debris after collisions. One of particles moving to a remote observer is necessarily near-critical. We discuss, when such a collision can give rise not only unboud E c.m. but also unbound Killing energy E (so-called super-Penrose process).Investigation of high energy collisions of particles near black holes comes back to works [1] - [3]. In recent years, an interest to this issue revived after the observation made by Bañados, Silk and West (the BSW effect, after the names of its authors) that particle collision near the Kerr black hole can lead, under certain additional conditions, to the unbounded growth of the energy in their centre of mass E c.m. [4]. Later on, in a large series of works, this observation was generalized and extended to other objects and scenarios. The energy that appears in the BSW effect is relevant for an observer who is present just near the point of collision in the vicinity of the black hole horizon. Meanwhile, what is especially physically important is the Killing energy E of debris after such a collision measured by an observer at infinity. Strong redshift "eats" significant part of E c.m. , so it was not quite clear in advance, to what extent the energy E may be high. If E exceeds the initial energy of particles, we are faced with the energy extraction from a black hole. This is a so-called collisional Penrose process (the Penrose process that occurs due to particle collisions). Thus there are two related but different issues: (i) investigation of the effect of unbounded E c.m. , (ii) study of properties of E and the question about the maximum possible efficiency of the collisional Penrose process.Consider the generic axially symmetric metric. It can be written asHere, the metric coefficients do not depend on t and φ. On the horizon N = 0. Alternatively, one can use coordinates θ and r, similar to Boyer-Lindquist ones for the Kerr metric, instead of l and z. In (1) we assume that the metric coefficients are even functions of z, so the equatorial plane θ = π 2 (z = 0) is a symmetry one.In the space-time under discussion there are two conserved quantities u 0 ≡ −E and u φ ≡ L where u μ = dx μ dτ is the four-velocity of a test particle, τ is the proper time and x μ = (t, φ, l, z) are coordinates..The aforementioned conserved quantities have the physical meaning of the energy per unit mass (or frequency for a lightlike particle) and azimuthal component of the angular momentum,

“…As far as small N is concerned, it turned out that for collisions near black holes, amplification of the energy is restricted [13] - [15] if both initial paricles moved along ingoing trajectories. If one of particles is on an outgoing trajectory, the energy E can be quite large [16], [17] or even formally unbound [10], [18] but in the latter case very special conditions are required and it is hard to satisfy them [19], [20]. Due to recent results [21], the super-Penrose process is possible for the case of naked singularity in collisions where also small N in the point of collision is required.…”

mentioning

confidence: 99%

“…One can ask -whether or not the efficiency of the energy extraction to infinity may also become unbound? (Following [10], we will use the term "super-Penrose process".) We can exploit the same classification in terms of three parameters (N, L, ω).…”

mentioning

confidence: 99%

Rapidly rotating spacetimes and collisional super-Penrose process

2016

Gen Relativ Gravit

We consider generic axially symmetric rotating spacetimes and examine particle collisions in the ergoregion. The results are generic and agree with those obtained in the particular case of the rotating Teo wormhole in N. Tsukamoto and C. Bambi, Phys. Rev. D 91, 104040 (2015). It is shown that for sufficiently rapid rotation, the energy of a particle escaping to infinity can become arbitrary large (so-called superPenrose process). Moreover, this energy is typically much larger than the center-of mass energy of colliding particles. In this sense the situation differs radically from that for collisions near black holes.