11,302 research outputs found
Oscillation modes of ultralight BEC dark matter cores
Structure formation simulations of ultralight bosonic dark matter, ruled by
the Gross-Pitaevskii-Poisson (GPP) system of equations, show that dark matter
clumps to form structures with density profiles consisting of a core surrounded
by a power-law distribution. The core has a density profile similar to that of
spherically symmetric equilibrium configurations of the GPP system. These
configurations have been shown to be stable under a variety of perturbations
and to have attractor properties. It is interesting to know the dominant
frequencies of oscillation of these configurations. One reason is that in
galaxies the effects of perturbations can trigger observable effects for
specific frequency modes. Another reason is that during the process of
structure formation, the oscillation modes can help to characterize a core.
Based on these motivations, in this manuscript we present a systematic
numerical analysis of the reaction of equilibrium configurations to various
axi-symmetric perturbations with modes . We then calculate the
first few oscillation frequencies of equilibrium configurations for each mode.Comment: 6 pages, 22 eps figures. Accepted for publication in Phys. Rev.
Answer to the Comment about the Letter entitled ``Scalar fields as dark matter in spiral galaxies''
In this manuscript the authors present a detailed answer to the comment in
order to avoid misunderstandings in the future.Comment: 3 pages, latex. An answer to a comment uploaded yesterday:
gr-qc/000605
Quintessence at Galactic Level?
Recently it has been proposed that the main contributor to the dark energy of
the Universe is a dynamical, slow evolving, spatially inhomogeneous scalar
field called quintessence. We investigate the behavior of this scalar field at
galactic level by assuming that it is the dark matter compossing the halos of
galaxies. Using an exact solution of the Einstein's equations we find an
excellent concordance between our results and observations.Comment: 3 pages, 2 .ps figures. Requires REVTe
Characterizing the velocity of a wandering black hole and properties of the surrounding medium using convolutional neural networks
We present a method for estimating the velocity of a wandering black hole and
the equation of state for the gas around, based on a catalog of numerical
simulations. The method uses machine learning methods based on convolutional
neural networks applied to the classification of images resulting from
numerical simulations. Specifically we focus on the supersonic velocity regime
and choose the direction of the black hole to be parallel to its spin. We build
a catalog of 900 simulations by numerically solving Euler's equations onto the
fixed space-time background of a black hole, for two parameters: the adiabatic
index with values in the range [1.1, 5/3], and the asymptotic relative
velocity of the black hole with respect to the surroundings , with
values within . For each simulation we produce a 2D image of the
gas density once the process of accretion has approached a stationary regime.
The results obtained show that the implemented Convolutional Neural Networks
are capable to classify correctly the adiabatic index of the time
within an uncertainty of while the prediction of the velocity is
correct of the times within an uncertainty of . We expect
that this combination of a massive number of numerical simulations and machine
learning methods will help analyze more complicated scenarios related to future
high resolution observations of black holes, like those from the Event Horizon
Telescope.Comment: 5 RevTex pages. Published in Physical Review
Accretion of supersonic winds onto black holes in 3D: stability of the shock cone
Using numerical simulations we present the accretion of supersonic winds onto
a rotating black hole in three dimensions. We study five representative
directions of the wind with respect to the axis of rotation of the black hole
and focus on the evolution and stability of the high density shock cone that is
formed during the process. We explore both, the regime in which the shock cone
is expected to be stable in order to confirm previous results obtained with two
dimensional simulations, and the regime in which the shock cone is expected to
show a flip-flop type of instability. The methods used to attempt triggering
the instability were first the accumulation of numerical errors and second the
explicit application of a perturbation on the velocity field after the
shock-cone was formed. The result is negative, that is, we did not find the
flip-flop instability within the parameter space we explored, which includes
cases that are expected to be unstable.Comment: 9 pages, 25 eps figures. Published in Ap
Spherical non-linear absorption of cosmological scalar fields onto a black hole
In this paper we track the non-linear spherical evolution of a massless
scalar field onto a Schwarzschild black hole space-time as a first
approximation to the accretion of cosmologically motivated classical scalar
fields. We perform an analysis related to wave packets described by wave number
and width. We study various values of the wave number k, and found that for k =
0 and width packets bigger than the Schwarzschild radius, the absorption is not
total. In the cases we studied for k > 0, the black hole absorbs the total
amount of energy density of the scalar field moving toward the horizon. Our
results indicate that assuming spherical symmetry, in the non-linear regime,
there are cases for which scalar fields are allowed to survive outside black
holes and may eventually have life-times consistent with cosmological time
scales.Comment: 7 revtex pages, accepted for publication in Phys. Rev.
Modeling long GRBs using a single shock with relativistic radiation hydrodynamics
We explore the possibility that a single relativistic shock, where the gas
dynamics is coupled with radiation, can fit the light curves of long GRBs. For
this we numerically solve the one dimensional relativistic radiation
hydrodynamics equations with a single initial shock. We calculate light curves
due to the evolution of this shock in terms of the velocity of the shock, the
opacity of the gas, mass density and density of radiated energy. We explore how
the variation of each of these parameters provides different features in the
light curves. As examples we include the fitting of two long GRBs.Comment: 11 pages, 10 figures, accepted for publication in MNRA
Spherical Boson Stars as Black Hole mimickers
We present spherically symmetric boson stars as black hole mimickers based on
the power spectrum of a simple accretion disk model. The free parameters of the
boson star are the mass of the boson and the fourth order self-interaction
coefficient in the scalar field potential. We show that even if the mass of the
boson is the only free parameter it is possible to find a configuration that
mimics the power spectrum of the disk due to a black hole of the same mass. We
also show that for each value of the self-interaction a single boson star
configuration can mimic a black hole at very different astrophysical scales in
terms of the mass of the object and the accretion rate. In order to show that
it is possible to distinguish one of our mimickers from a black hole we also
study the deflection of light.Comment: 8 revtex pages, 10 eps figure
Rotation curves of ultralight BEC dark matter halos with rotation
We study the rotation curves of ultralight BEC dark matter halos. These halos
are long lived solutions of initially rotating BEC fluctuations. In order to
study the implications of the rotation characterizing these long-lived
configurations we consider the particular case of a boson mass
and no self-interaction. We find that these halos
successfully fit samples of rotation curves (RCs) of LSB galaxies.Comment: 7 pages, 10 eps figures, 1 tables. Accepted for publication in
General Relativity and Gravitatio
Estimating the contribution of Alfv\'en waves to the process of heating the quiet solar corona
We solve numerically the ideal MHD equations with an external gravitational
field in 2D in order to study the effects of impulsively generated linear and
non-linear Alfv\'en waves into isolated solar arcades and coronal funnels. We
analyze the region containing the interface between the photosphere and the
corona. The main interest is to study the possibility that Alfv\'en waves
triggers the energy flux transfer toward the quiet solar corona and heat it,
including the case that two consecutive waves can occur. We find that in the
case of arcades, short or large, the transferred fluxes by Alfv\'en waves are
sufficient to heat the quiet corona only during a small lapse of time and in a
certain region. In the case of funnels the threshold is achieved only when the
wave is faster than 10 km/s, which is extremely high. We conclude from our
analysis, that Alfv\'en waves, even in the optimistic scenario of having two
consecutive Alfv\'en wave pulses, cannot transport enough energy as to heat the
quiet corona.Comment: 13 pages, 48 png figures. Accepted for publication in MNRA
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