1,831 research outputs found
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
Relativistic Static Thin Disks of Polarized Matter
An infinite family of exact solutions of the electrovacuum Einstein-Maxwell
equations is presented. The family is static, axially symmetric and describe
thin disks composed by electrically polarized material in a conformastatic
spacetime. The form of the conformastatic metric allows us to write down the
metric functions and the electromagnetic potentials in terms of a solution of
the Laplace equation. We find a general expression for the surface energy
density of the disk, the pressure, the polarization vector, the electromagnetic
fields and the velocity rotation for circular orbits. As an example, we present
the first model of the family and show the behavior of the different physical
variables.Comment: 7 pages, 4 figures, 70 and 70 Gravitation Fest, 28 September 2016,
Cartagena, Colombi
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
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,
In Pres
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
Bondi-Hoyle-Lyttleton accretion in the presence of small rigid bodies around a black hole
We study the relativistic Bondi-Hoyle-Lyttleton accretion onto a
Schwarzschild black hole (BH), which is surrounded by rigid and small, randomly
distributed, bodies. These bodies are idealized representations of substructure
like stars passing close to the BH, bubbles created by stellar winds or cold
clumps.We explore cases where the filling factor of these bodies is small. The
flow is assumed to be adiabatic and move supersonically towards the black hole.
The interaction with these rigid obstacles transforms ram pressure of the flow
into thermal pressure through bow shocks, slowing down the flow and making the
accreting gas turbulent. As a consequence, although the flow reaches a
statistically-steady state, the accretion rate presents some variability. For a
flow Mach number at infinity of 4, a few of these objects (5 - 10) are enough
to increase the accretion rate about 50% over the accretion rate without
bodies, even though the gas is adiabatic and the filling factor of the
obstacles is small.Comment: 8 pages, 13 figures, 1 table. Accepted for publication in Monthly
Notices of the Royal Astronomical Societ
PBH mass growth through radial accretion during the radiation dominated era
We model the radial accretion of radiation on Primordial Black Holes (PBH) by
numerically solving Einstein's equations coupled to an ultrarelativistic ideal
gas with equation of state . We calculate the final mass of a black
hole by the integration of the accreted radiation energy density during the
leptonic era between to after the Big Bang. Our
results indicate that small PBHs with initial masses between to
may grow up to hundreds of solar masses, and thus can be SMBH
seeds. On the other hand, PBHs formed at with initial mass between
900 and , by the time show masses of to
which are masses of seeds or already formed SMBHs. The fact
that we consider only radial flow implies that our results work well as
limiting cases, and it is expected that under more general scenarios the
accretion rates may change significantly. Nevertheless we show that it is
possible that SMBHs can be PBHs that grew due to the accretion of radiation.Comment: 15 pages, 6 eps figures. Accepted for publication in JCA
General Relativistic Razor-Thin Disks with Magnetically Polarized Matter
The origin of magnetic fields in the universe still remains unknown and
constitutes one of the most intriguing questions in astronomy and astrophysics.
Their significance is enormous since they have a strong influence on many
astrophysical phenomena. In regards of this motivation, theoretical models of
galactic disks with sources of magnetic field may contribute to understand the
physics behind them. Inspired by this, we present a new family of analytical
models for thin disks composed by magnetized material. The solutions are
axially symmetric, conformastatic and are obtained by solving the
Einstein-Maxwell Field Equations for continuum media without the test field
approximation, and assuming that the sources are razor-thin disk of
magnetically polarized matter. We find analytical expressions for the surface
energy density, the pressure, the polarization vector, the electromagnetic
fields, the mass and the rotational velocity for circular orbits, for two
particular solutions. In each case, the energy-momentum tensor agrees with the
energy conditions and also the convergence of the mass for all the solutions is
proved. Since the solutions are well-behaved, they may be used to model
astrophysical thin disks, and also may contribute as initial data in numerical
simulations. In addition, the process to obtain the solutions is described in
detail, which may be used as a guide to find solutions with magnetized material
in General Relativity.Comment: 18 pages, 11 .pdf figures, Accepted for publication in General
Relativity and Gravitatio
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