735 research outputs found
Collapse of Charged Scalar Field in Dilaton Gravity
We elaborated the gravitational collapse of a self-gravitating complex
charged scalar field in the context of the low-energy limit of the string
theory, the so-called dilaton gravity. We begin with the regular spacetime and
follow the evolution through the formation of an apparent horizon and the final
central singularity.Comment: 36 pages, 51 figures, to be published in Phys.Rev.D1
On the duration of long GRBs: effects of black hole spin
In the frame of the collapsar model for long gamma ray bursts (GRBs), we
investigate the formation of a torus around a spinning BH and we check what
rotational properties a progenitor star must have in order to sustain torus
accretion over relatively long activity periods. We also study the time
evolution of the BH spin parameter. We take into account the coupling between
BH mass, its spin parameter and the critical specific angular momentum of
accreting gas, needed for the torus to form. The large BH spin reduces the
critical angular momentum which in turn can increase the GRB duration with
respect to the Schwarzschild BH case. We quantify this effect and estimate the
GRB durations in three cases: when a hyper accreting torus operates or a BH
spins very fast or both. We show under what conditions a given progenitor star
produces a burst that can last as short as several seconds and as long as
several hundred of seconds. Our models indicate that it is possible for a
single collapse to produce three kinds of jets: (1) a very short, lasting
between a fraction of a second and a few seconds, 'precursor' jet, powered only
by a hyper accreting torus before the BH spins up, (2) an 'early' jet, lasting
several tens of seconds and powered by both hyper accretion and BH rotation,
and (3) a 'late' jet, powered only by the spinning BH.Comment: 13 pages; 9 figures; ApJ in pres
Static configurations and evolution of higher dimensional brane-dilaton black hole system
Static configurations and a dynamical evolution of the system composed of a
higher-dimensional spherically symmetric dilaton black hole and the
Dirac-Goto-Nambu brane were investigated. The studies were conducted for three
values of the dilaton coupling constant, describing the uncoupled case, the
low-energy limit of the string theory and dimensionally reduced Klein-Kaluza
theories. When the black hole is nonextremal, two types of static
configurations are observed, a brane which intersects the black hole horizon
and a brane not having any common points with the accompanying black hole. As
the number of spacetime dimensions increases, the brane bend in the vicinity of
the black hole disappears closer to its horizon. Dynamical evolution of the
system results in an expulsion of the black hole from the brane. It proceeds
faster for bigger values of the bulk spacetime dimension and thicker branes.
The value of the dilatonic coupling constant does not influence neither the
static configurations nor the dynamical behavior of the examined nonextremal
system. In the extremal dilaton black hole case one obtains expulsion of the
brane which is independent on the spacetime dimensionality and the value of the
coupling constant. Dynamical studies of the configurations in the extremal case
reveal that the course of evolution of the system is similar to the nonextremal
one, except for a slightly earlier expulsion of the black hole from the brane.Comment: 23 pages, 7 figure
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