1,482 research outputs found
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.
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
Non Axisymmetric Relativistic Wind Accretion with Velocity Gradients onto a Rotating Black Hole
We model, for the first time, the Bondi-Hoyle accretion of a fluid with
velocity gradients onto a Kerr black hole, by numerically solving the fully
relativistic hydrodynamics equations. Specifically, we consider a supersonic
ideal gas, which has velocity gradients perpendicular to the relative motion.
We measure the mass and specific angular accretion rates to illustrate whether
the fluid presents unstable patterns or not. The initial parameters, we
consider in this work, are the velocity gradient , the black hole
spin , the asymptotic Mach number and adiabatic index
. We show that the flow accretion reaches a fairly stationary regime,
unlike in the Newtonian case, where significant fluctuations of the mass and
angular momentum accretion rates are found. On the other hand, we consider a
special case where both density and velocity gradients of the fluid are taken
into account. The spin of the black hole and the asymptotic Newtonian Mach
number, for this case, are and , respectively. A
kind of flip-flop behavior is found at the early times; nevertheless, the
system also reaches a steady state.Comment: 11 pages, 20 figures, 1 table. Accepted for publication in MNRA
Horizon growth of supermassive black hole seeds fed with collisional dark matter
We present the accretion of collisional dark matter on a supermassive black
hole seed. The analysis is based on the numerical solution of the fully coupled
system of Einstein-Euler equations for spherically symmetric flow, where the
dark matter is modeled as a perfect fluid that obeys an ideal gas equation of
state. As the black hole actually grows, the accretion rate of dark matter
corresponds to the black hole apparent horizon growth rate. We analyse cases
with infall velocity as high as and an environment density of
, which are rather extreme conditions. Being the
radial flux the maximum accretion case, our results show that the accretion of
an ideal gas, eventually collisional dark matter, does not contribute
significantly to SMBH masses. This result favors models predicting SMBHs were
formed already with supermasses. We show that despite the fact that we are
solving the full general relativistic system, for the parameter space studied
our results are surprisingly similar to those obtained using the Bondi formula,
which somehow certifies its use as a good approximation of a fully evolving
space-time with spherical symmetry at short scales at least for dark matter
densities. Additionally, we study the density profile of the gas and find that
the presence of SMBHs redistributes the gas near the event horizon with a cuspy
profile, whereas beyond a small fraction of a parsec it is not-cuspy anymore.Comment: 11 pages, 6 eps figures, 3 tables. Accepted for publication in MNRA
On the conservation of the Jacobi integral in the post-Newtonian circular restricted three-body problem
In the present paper, using the first-order approximation of the -body
Lagrangian (derived on the basis of the post-Newtonian gravitational theory of
Einstein, Infeld, and Hoffman), we explicitly write down the equations of
motion for the planar circular restricted three-body problem. Additionally,
with some simplified assumptions, we obtain two formulas for estimating the
values of the mass/distance and velocity/speed of light ratios appropriate for
a given post-Newtonian approximation. We show that the formulas derived in the
present study, lead to a good numerical conservation of the Jacobi constant and
allow for an approximate equivalence between the Lagrangian and Hamiltonian
approaches at the same post-Newtonian order. Accordingly, the dynamics of the
system is analyzed in terms of the Poincar\'e sections method and Lyapunov
exponents, finding that for specific values of the Jacobi constant the dynamics
can be either chaotic or regular. Our results suggest that the chaoticity of
the post-Newtonian system is slightly in- creased in comparison with its
Newtonian counterpart.Comment: 13 pages, 6 figures. This version has been substantially revised.
Some new results were adde
Is the flip-flop behaviour of accretion shock cones on to black holes an effect of coordinates?
We study numerically the relativistic Bondi-Hoyle accretion of an ideal gas
onto a Kerr fixed background space-time on the equatorial plane with s-lab
symmetry. We use both Kerr-Schild (KS) and Boyer-Lindquist (BL) coordinates. We
particularly focus on the study of the flip-flop motion of the shock cone
formed when the gas is injected at supersonic speed. The development of the
flip-flop instability of the shock cone in the relativistic regime was reported
recently for the first time. We reproduce the flip-flop behaviour found in the
past when BL coordinates are used, and perform similar numerical experiments
using horizon penetrating KS coordinates. We find that when using KS
coordinates the shock cone oscillates, however such oscillations are not of the
flip-flop type and their amplitude decrease with resolution.Comment: 8 pages, 9 eps figures, accepted for publication in MNRA
Evolution of a mass-less test scalar field on Boson Stars space-times
We numerically solve the mass-less test scalar field equation on the
space-time background of boson stars and black holes. In order to do so, we use
a numerical domain that contains future null infinity. We achieve this
construction using a scri-fixing conformal compactification technique based on
hyperboloidal constant mean curvature foliations of the space-time and solve
the conformally invariant wave equation. We present two results: the scalar
field shows oscillations of the quasi- normal-mode type found for black holes
only for boson star configurations that are compact, and no signs of tail decay
is found in the parameter space we explored. Even though our results do not
correspond to the master equation of perturbations of boson star solutions,
they indicate that the parameter space of boson stars as black hole mimickers
is restricted to compact configurations.Comment: 9 pages, 15 eps figures, revtex
CAFE: A New Relativistic MHD Code
We introduce CAFE, a new independent code designed to solve the equations of
Relativistic ideal Magnetohydrodynamics (RMHD) in 3D. We present the standard
tests for a RMHD code and for the Relativistic Hydrodynamics (RHD) regime since
we have not reported them before. The tests include the 1D Riemann problems
related to blast waves, head-on collision of streams and states with transverse
velocities, with and without magnetic field, which is aligned or transverse,
constant or discontinuous across the initial discontinuity. Among the 2D and 3D
tests, without magnetic field we include the 2D Riemann problem, a one
dimensional shock tube along a diagonal, the high speed Emery wind tunnel, the
Kelvin-Helmholtz instability, a set of jets and a 3D spherical blast wave,
whereas in the presence of a magnetic field we show the magnetic rotor, the
cylindrical explosion, a case of Kelvin-Helmholtz instability and a 3D magnetic
field advection loop. The code uses High Resolution Shock Capturing methods and
we present the error analysis for a combination that uses the HLLE flux formula
combined with linear, PPM and fifth order WENO reconstructors. We use the
flux-CT and the divergence cleaning methods to control the divergence free
magnetic field constraint.Comment: 30 pages, 110 png figures, 4 tables. Accepted for publication in the
Astrophysical Journal Supplement. More numerical details, tests and
additional reference
Revisiting spherically symmetric relativistic hydrodynamics
In this paper we revise two classical examples of Relativistic Hydrodynamics
in order to illustrate in detail the numerical methods commonly used in fluid
dynamics, specifically those designed to deal with shocks, which are based on a
finite volume approximation. The two cases we consider are the relativistic
blast wave problem and the evolution of a Tolman-Oppenheimer-Volkoff star
model, in spherical symmetry. In the first case we illustrate the
implementation of relativistic Euler's equations on a fixed background
space-time, whereas in the second case we also show how to couple the evolution
of the fluid to the evolution of the space-time.Comment: Prepared with educative purposes, 15 pages, 34 eps figure
Pseudo-Newtonian planar circular restricted 3-body problem
We study the dynamics of the planar circular restricted three-body problem in
the context of a pseudo-Newtonian approximation. By using the
Fodor-Hoenselaers-Perj\'es procedure, we perform an expansion in the mass
potential of a static massive spherical source up to the first non-Newtonian
term, giving place to a gravitational potential that includes first-order
general relativistic effects. With this result, we model a system composed by
two pseudo-Newtonian primaries describing circular orbits around their common
center of mass, and a test particle orbiting the system in the equatorial
plane. The dynamics of the new system of equations is studied in terms of the
Poincar\'e section method and the Lyapunov exponents, where the introduction of
a new parameter , allows us to observe the transition from the
Newtonian to the pseudo-Newtonian regime. We show that when the Jacobian
constant is fixed, a chaotic orbit in the Newtonian regime can be either
chaotic or regular in the pseudo-Newtonian approach. As a general result, we
find that most of the pseudo-Newtonian configurations are less stable than
their Newtonian equivalent.Comment: 11 pages, 2 figures. Accepted for publication in Physics Letters A,
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