Circular orbits and acceleration of particles by near-extremal dirty rotating black holes: general approach

2012

J. High Energ. Phys.

We consider collision of two geodesic particles moving around rotating stationary axially symmetric black holes. It is shown for arbitrary nonequatorial motion that under certain conditions the energy in their centre of mass frame can grow unbound (the so-called BSW effect). This generalizes the previous results for equatorial motion around dirty (surrounded by matter) black holes and nonequatorial motion around the Kerr metric. It turns out that the BSW effect occurs near any point of the horizon surface. We do not use special symmetries of space-time typical of the Kerr metric, so the results are quite generic. The general scheme classifying all possible scenarios is discussed.

“…In the region η > 0, a particle should be near-critical (not exactly critical) with C satisfying eq. (18). Here, the quantities g H and B depend, in general, on θ.…”

Section: B Kinematic Conditionsmentioning

confidence: 99%

“…Here, the quantities g H and B depend, in general, on θ. Therefore, if one wants to arrange collision between particles near the point on the horizon with some value θ * of the polar angle, the corresponding minimum value of C also depends on θ * according to (18). If m ≪ E, condition (18) simplifies to…”

Section: B Kinematic Conditionsmentioning

confidence: 99%

Ultra-high energy collisions of nonequatorial geodesic particles near dirty black holes

2012

J. High Energ. Phys.

“…For a generic dirty black hole (1) it is impossible to find the solution analytically at all. However, it turns out that if a nonextremal black hole is close to its extremal state, there are some general features that enabled us to develop a general approach to the analysis of such orbits [12]. If the surface gravity κ = 1 2 ( ∂N 2 ∂ρ ) ρ=ρ H of a black hole is small (κ = 0 corresponds to the extremal state), then, it turns out that for ISCO…”

Section: Circular Orbits For Near-extremal Black Holesmentioning

confidence: 99%

“…This quantity remains finite in any act of collision, although it can become as large as one likes (this can be called "the kinematic censorship"). The relation between the high energy collisions and properties of ISCO close to the horizon was considered first in [5] for the near-extremal Kerr metric and generalized in [12] for dirty black holes. In the present paper, we discuss the aforementioned relation both for near-extremal and extremal black holes.…”

Section: Introductionmentioning

confidence: 99%

Near-horizon circular orbits and extremal limit for dirty rotating black holes

2015

Phys. Rev. D

We consider generic rotating axially symmetric "dirty" (surrounded by matter) black holes. Near-horizon circular equatorial orbits are examined in two different cases of near-extremal (small surface gravity κ) and exactly extremal black holes.This has a number of qualitative distinctions. In the first case, it is shown that such orbits can lie as close to the horizon as one wishes on suitably chosen slices of space-time when κ → 0. This generalizes observation of T. Jacobson Class.Quantum Grav. 28 187001 (2011) made for the Kerr metric. If a black hole is extremal (κ = 0), circular on-horizon orbits are impossible for massive particles but, in general, are possible in its vicinity. The corresponding black hole parameters determine also the rate with which a fine-tuned particle on the noncircular nearhorizon orbit asymptotically approaches the horizon. Properties of orbits under discussion are also related to the Bañados-Silk-West effect of high energy collisions near black holes. Impossibility of the on-horizon orbits in question is manifestation of kinematic censorship that forbids infinite energies in collisions.

“…In case (ii), no fine-tuning is required [2] - [4]. There is also one more case (iii), when fine-tuning of parameters itself is the consequence of the fact that a particle moved on a circular orbit, provided this orbit is situated near the horizon of a near-extremal black hole [5], [6].…”

Section: Introductionmentioning

confidence: 99%

General limitations on trajectories suitable for super-Penrose process

2015

EPL

Collisions of particles near a rotating black hole can lead to unbound energies E c.m.in their centre of mass frame. There are indications that the Killing energy of debris at infinity can also be unbound for some scenarios of collisions near the extremal black hole horizon (so-called super-Penrose process). They include participation of a particle that (i) has generic (not fine-tuned) parameters and (ii) moves away from a black hole before collision. We show that for any finite particle's mass, such a particle cannot be obtained as a result of the preceding collision. However, this can be done if one of initial infalling particles has the mass of the order N −2 that generalizes previous observations made in literature for radial infall in the Kerr background.