25 research outputs found
Banados-Silk-West effect with nongeodesic particles: Nonextremal horizons
When two particles collide near a black hole, the energy in their center of
mass frame can, under certain conditions, grow unbounded. This is the
Banados-Silk-West effect. We show that this effect retains its validity even if
some force acts on a particle, provided some reasonable and weak restrictions
are imposed on this force. In the present work we discuss the case of
nonextremal horizons. The result under discussion is similar to that for
extremal horizons considered in our previous work.Comment: v2 matches the published version; revtex4, 11 page
Dirty rotating black holes: regularity conditions on stationary horizons
We consider generic, or "dirty" (surrounded by matter), stationary rotating
black holes with axial symmetry. The restrictions are found on the asymptotic
form of metric in the vicinity of non-extremal, extremal and ultra-extremal
horizons, imposed by the conditions of regularity of increasing strength:
boundedness on the horizon of the Ricci scalar, of scalar quadratic curvature
invariants, and of the components of the curvature tensor in the tetrad
attached to a falling observer. We show, in particular, that boundedness of the
Ricci scalar implies the "rigidity" of the horizon's rotation in all cases,
while the finiteness of quadratic invariants leads to the constancy of the
surface gravity. We discuss the role of quasiglobal coordinate r that is
emphasized by the conditions of regularity. Further restrictions on the metric
are formulated in terms of subsequent coefficients of expansion of metric
functions by r. The boundedness of the tetrad components of curvature tensor
for an observer crossing the horizon is shown to lead in the horizon limit to
diagonalization of Einstein tensor in the frame of zero angular momentum
observer on a circular orbit (ZAMO frame) for horizons of all degrees of
extremality.Comment: 31 pages. Misprints correcte