5,767 research outputs found
BLACK HOLES IN THREE-DIMENSIONAL DILATON GRAVITY THEORIES
Three dimensional black holes in a generalized dilaton gravity action theory
are analysed. The theory is specified by two fields, the dilaton and the
graviton, and two parameters, the cosmological constant and the Brans-Dicke
parameter. It contains seven different cases, of which one distinguishes as
special cases, string theory, general relativity and a theory equivalent to
four dimensional general relativity with one Killing vector. We study the
causal structure and geodesic motion of null and timelike particles in the
black hole geometries and find the ADM masses of the different solutions.Comment: 19 pages, latex, 4 figures as uuencoded postscript file
Charged polytropic compact stars
In this work, we analyze the effect of charge in compact stars considering
the limit of the maximum amount of charge they can hold. We find that the
global balance of the forces allows a huge charge (~ 10^{20} Coulomb) to be
present in a neutron star producing a very high electric field (~ 10^{21} V/m).
We have studied the particular case of a polytropic equation of state and
assumed that the charge distribution is proportional to the mass density. The
charged stars have large mass and radius as we should expect due to the effect
of the repulsive Coulomb force with the M/R ratio increasing with charge. In
the limit of the maximum charge the mass goes up to ~ 10 M_sun which is much
higher than the maximum mass allowed for a neutral compact star. However, the
local effect of the forces experienced by a single charged particle, makes it
to discharge quickly. This creates a global force imbalance and the system
collapses to a charged black hole
The Three-Dimensional BTZ Black Hole as a Cylindrical System in Four-Dimensional General Relativity
It is shown how to transform the three dimensional BTZ black hole into a four
dimensional cylindrical black hole (i.e., black string) in general relativity.
This process is identical to the transformation of a point particle in three
dimensions into a straight cosmic string in four dimensions.Comment: Latex, 9 page
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