Paper: astro-ph/0505450
Date: Fri, 20 May 2005 20:00:12 GMT (222kb)

Title: Black hole-neutron star binaries in general relativity: effects of
neutron star spin
Authors: Keisuke Taniguchi, Thomas W. Baumgarte, Joshua A. Faber, and Stuart L.
Shapiro
Comments: 27 pages, 34 eps figures, submitted to Phys. Rev. D
\\
We present new sequences of general relativistic, quasiequilibrium black
hole-neutron star binaries. We solve for the gravitational field in the
conformal thin-sandwich decomposition of Einstein's field equations, coupled to
the equations of relativistic hydrostatic equilibrium for a perfect fluid. We
account for the black hole by solving these equations in the background metric
of a Schwarzschild black hole whose mass is much larger than that of the
neutron star. The background metric is treated in Kerr-Schild as well as
isotropic coordinates. For the neutron star, we assume a polytropic equation of
state with adiabatic index Gamma=2, and solve for both irrotational and
corotational configurations. By comparing the results of irrotational and
synchronized configurations with the same background metric, we conclude that
the effect of the rotation on the location of tidal break-up is only on the
order of a few percent. The different choices in the background also lead to
differences of order a few percent, which may be an indication of the level to
which these configurations approximate quasiequilibrium.
\\ ( http://arXiv.org/abs/astro-ph/0505450 , 222kb)
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Paper: astro-ph/0505454
Date: Sat, 21 May 2005 21:11:01 GMT (162kb)

Title: Oscillations of Thick Accretion Discs Around Black Holes - II
Authors: Eduardo Rubio-Herrera and William H. Lee
Comments: 10 pages, 8 figures, accepted for publication as a paper in the
Monthly Notices of the Royal Astronomical Society
\\
We present a numerical study of the global modes of oscillation of thick
accretion discs around black holes. We have previously studied the case of
constant distributions of specific angular momentum. In this second paper, we
investigate (i) how the size of the disc affects the oscillation
eigenfrequencies, and (ii) the effect of power-law distributions of angular
momentum on the oscillations. In particular, we compare the oscillations of the
disc with the epicyclic eigenfrequencies of a test particle with different
angular momentum distributions orbiting around the central object. We find that
there is a frequency shift away from the epicyclic eigenfrequency of the test
particle to lower values as the size of the tori is increased. We have also
studied the response of a thick accretion disc to a localized external
perturbation using non constant specific angular momentum distributions within
the disc. We find that in this case it is also possible (as reported previously
for constant angular momentum distributions) to efficiently excite internal
modes of oscillation. In fact we show here that the local perturbations excite
global oscillations (acoustic p modes) closely related to the epicyclic
oscillations of test particles. Our results are particularly relevant in the
context of low mass X-ray binaries and microquasars, and the high frequency
Quasi-Periodic Oscillations (QPOs) observed in them. Our computations make use
of a Smooth Particle Hydrodynamics (SPH) code in azimuthal symmetry, and use a
gravitational potential that mimics the effects of strong gravity.
\\ ( http://arXiv.org/abs/astro-ph/0505454 , 162kb)

Paper: astro-ph/0505460
Date: Sat, 21 May 2005 21:15:25 GMT (12kb)

Title: Neutrino asymmetry around black holes: Neutrinos interact with gravity
Authors: Banibrata Mukhopadhyay
Comments: 10 pages. To appear in Modern Physics Letters A
\\
Propagation of a fermion in curved space-time generates a gravitational
interaction due to coupling of its spin with the space-time curvature
connection. This gravitational interaction, which is an axial-four-vector
multiplied by a four gravitational vector potential, appears as a CPT violating
term in the Lagrangian which generates an opposite sign and thus asymmetry
between the left-handed and the right handed partners under the CPT
transformation. In the case of neutrinos, this property can generate a neutrino
asymmetry in the Universe. If the background metric is of the rotating black
hole, i.e. the Kerr geometry, this interaction for the neutrino is non-zero.
Therefore, the dispersion energy relations for the neutrino and its
anti-neutrino are different which give rise to the difference in their number
densities and the neutrino asymmetry in the Universe in addition to the known
relic asymmetry.
\\ ( http://arXiv.org/abs/astro-ph/0505460 , 12kb)
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Paper: astro-ph/0505463
Date: Sun, 22 May 2005 17:16:38 GMT (372kb)

Title: Formation and Evolution of Supermassive Black Holes
Authors: Francoise Combes (LERMA, Observatoire de Paris)
Comments: 31 pages, 13 figures, review paper for Astrophysics Update 2
\\
The correlation between the mass of supermassive black holes in galaxy nuclei
and the mass of the galaxy spheroids or bulges (or more precisely their central
velocity dispersion), suggests a common formation scenario for galaxies and
their central black holes. The growth of bulges and black holes can commonly
proceed through external gas accretion or hierarchical mergers, and are both
related to starbursts. Internal dynamical processes control and regulate the
rate of mass accretion. Self-regulation and feedback are the key of the
correlation. It is possible that the growth of one component, either BH or
bulge, takes over, breaking the correlation, as in Narrow Line Seyfert 1
objects. The formation of supermassive black holes can begin early in the
universe, from the collapse of Population III, and then through gas accretion.
The active black holes can then play a significant role in the re-ionization of
the universe. The nuclear activity is now frequently invoked as a feedback to
star formation in galaxies, and even more spectacularly in cooling flows. The
growth of SMBH is certainly there self-regulated. SMBHs perturb their local
environment, and the mergers of binary SMBHs help to heat and destroy central
stellar cusps. The interpretation of the X-ray background yields important
constraints on the history of AGN activity and obscuration, and the census of
AGN at low and at high redshifts reveals the downsizing effect, already
observed for star formation. History appears quite different for bright QSO and
low-luminosity AGN: the first grow rapidly at high z, and their number density
decreases then sharply, while the density of low-luminosity objects peaks more
recently, and then decreases smoothly.

\\ ( http://arXiv.org/abs/astro-ph/0505463 , 372kb)