arXiv subjects

F. D. Lora-Clavijo

Publications and source records attributed to F. D. Lora-Clavijo.

50 records · Page 3Linked to original sources

arXiv2013

Stability of BEC galactic dark matter halos

In this paper we show that spherically symmetric BEC dark matter halos, with the $\sin r/r$ density profile, that accurately fit galactic rotation curves and represent a potential solution to the cusp-core problem are unstable. We do this by introducing back the density profiles into the fully time-dependent Gross-Pitaevskii-Poisson system of equations. Using numerical methods to track the evolution of the system, we found that these galactic halos lose mass at an approximate rate of half of its mass in a time scale of dozens of Myr. We consider this time scale is enough as to consider these halos are unstable and unlikely to be formed. We provide some arguments to show that this behavior is general and discuss some other drawbacks of the model that restrict its viability.

astro-ph.CO↗

arXiv2013

The shocks during the accretion of an ultrarelativistic supersonic gas onto a rotating black hole

In this work, we track the evolution of an ultrarelativistic fluid onto a Kerr black hole, on the equatorial plane. In this treatment, we consider the limit where the rest mass density is neglected, that is, the approximation is valid in the regime where the internal energy dominates over the rest mass density. We particularly concentrate in the case of a gas with $Γ$ = 4/3, which corresponds to a radiation fluid. We show, as in several cases, that a shock cone appears when the asymptotic velocity of the fluid is larger than the asymptotic relativistic sound speed of the gas. On the other hand, in order to show the system approaches to steady state, we calculate the accreted total energy rate on a spherical surface. Finally, we also show the gas distribution and various of its properties.

astro-ph.HE↗

arXiv2013

Exact solution of the 1D Riemann problem in Newtonian and relativistic hydrodynamics

Some of the most interesting scenarios that can be studied in astrophysics, contain fluids and plasma moving under the influence of strong gravitational fields. To study these problems it is required to implement numerical algorithms robust enough to deal with the equations describing such scenarios, which usually involve hydrodynamical shocks. It is traditional that the first problem a student willing to develop research in this area is to numerically solve the one dimensional Riemann problem, both Newtonian and relativistic. Even a more basic requirement is the construction of the exact solution to this problem in order to verify that the numerical implementations are correct. We describe in this paper the construction of the exact solution and a detailed procedure of its implementation.

astro-ph.HE↗

arXiv2012

Axisymmetric Bondi-Hoyle accretion onto a Schwarzschild Black Hole: shock cone vibrations

We study numerically the axisymmetric relativistic Bondi-Hoyle accretion of a supersonic ideal gas onto a fixed Schwarzschild background space-time described with horizon penetrating coordinates. We verify that a nearly stationary shock cone forms and that the properties of the shock cone are consistent with previous results in Newtonian gravity and former relativistic studies. The fact that the evolution of the gas is tracked on a spatial domain that contains a portion of the inner part of the black hole avoids the need to impose boundary conditions on a time-like boundary as done in the past. Thus, our approach contributes to the solution to the Bondi-Hoyle accretion problem at the length scale of the accretor in the sense that the gas is genuinely entering the black hole. As an astrophysical application, we study for a set of particular physical parameters, the spectrum of the shock cone vibrations and their potential association with QPO sources.

astro-ph.HE↗

arXiv2012

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.

gr-qc↗

arXiv2012

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.

astro-ph.HE↗

arXiv2012

Behavior of Phantom Scalar Fields near Black Holes

We present the accretion of a phantom scalar field into a black hole for various scalar field potentials in the full non-linear regime. Our results are based on the use of numerical methods and show that for all the cases studied the black hole's apparent horizon mass decreases. We explore a particular subset of the parameter space and from our results we conclude that this is a very efficient black hole shrinking process because the time scales of the area reduction of the horizon are short. We show that the radial equation of state of the scalar field depends strongly on the space and time, with the condition $ω= p/ρ>-1$, as opposed to a phantom fluid at cosmic scales that allows $ω< -1$.

astro-ph.CO↗

arXiv2012

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.

astro-ph.CO↗

arXiv2011

Scalar Field Dark Matter: behavior around black holes

We present the numerical evolution of a massive test scalar fields around a Schwarzschild space-time. We proceed by using hyperboloidal slices that approach future null infinity, which is the boundary of scalar fields, and also demand the slices to penetrate the event horizon of the black hole. This approach allows the scalar field to be accreted by the black hole and to escape toward future null infinity. We track the evolution of the energy density of the scalar field, which determines the rate at which the scalar field is being diluted. We find polynomial decay of the energy density of the scalar field, and use it to estimate the rate of dilution of the field in time. Our findings imply that the energy density of the scalar field decreases even five orders of magnitude in time scales smaller than a year. This implies that if a supermassive black hole is the Schwarzschild solution, then scalar field dark matter would be diluted extremely fast

astro-ph.CO↗

arXiv2011

Collisional dark matter density profiles around supermassive black holes

We solve the spherically symmetric time dependent relativistic Euler equations on a Schwarzschild background space-time for a perfect fluid, where the perfect fluid models the dark matter and the space-time background is that of a non-rotating supermassive black hole. We consider the fluid obeys an ideal gas equation of state as a simple model of dark matter with pressure. Assuming out of equilibrium initial conditions we search for late-time attractor type of solutions, which we found to show a constant accretion rate for the non-zero pressure case, that is, the pressure itself suffices to produce stationary accretion regimes. We then analyze the resulting density profile of such late-time solutions with the function $A/r^κ$. For different values of the adiabatic index we find different slopes of the density profile, and we study such profile in two regions: a region one near the black hole, located from the horizon up to 50$M$ and a region two from $\sim 800M$ up to $\sim 1500M$, which for a black hole of $10^{9}M_{\odot}$ corresponds to $\sim 0.1$pc. The profile depends on the adiabatic index or equivalently on the pressure of the fluid and our findings are as follows: in the near region the density profile shows values of $κ<1.5$ and in the limit of the pressure-less case $κ\rightarrow 1.5$; on the other hand, in region two, the value of $κ<0.3$ in all the cases we studied. If these results are to be applied to the dark matter problem, the conclusion is that, in the limit of pressure-less gas the density profile is cuspy only near the black hole and approaches a non-cuspy profile at bigger scales within 1pc. These results show on the one hand that pressure suffices to provide flat density profiles of dark matter and on the other hand show that the presence of a central black hole does not distort the density profile of dark matter at scales of 0.1pc.

astro-ph.GA↗

arXiv2011

Exploring the effects of pressure on the radial accretion of dark matter by a Schwarzschild supermassive black hole

Based on the numerical solution of the time-dependent relativistic Euler equations onto a fixed Schwarzschild background space-time, we estimate the accretion rate of radial flow toward the horizon of a test perfect fluid obeying an ideal gas equation of state. We explore the accretion rate in terms of the initial density of the fluid for various values of the inflow velocity in order to investigate whether or not sufficiently arbitrary initial conditions allow a steady state accretion process depending on the values of the pressure. We extrapolate our results to the case where the fluid corresponds to dark matter and the black hole is a supermassive black hole seed. Then we estimate the equation of state parameters that provide a steady state accretion process. We found that when the pressure of the dark matter is zero, the black hole's mass grows up to values that are orders of magnitude above $10^{9}M_{\odot}$ during a lapse of 10Gyr, whereas in the case of the accretion of the ideal gas dark matter with non zero pressure the accreted mass can be of the order of $\sim 1M_{\odot}/10Gyr$ for black holes of $10^{6}M_{\odot}$. This would imply that if dark matter near a supermassive black hole acquires an equation of state with non trivial pressure, the contribution of accreted dark matter to the supermassive black hole growth could be small, even though only radial accretion is considered.

astro-ph.GA↗

arXiv2010

Charged Annular Disks and Reissner-Nordström Type Black Holes from Extremal Dust

We present the first analytical superposition of a charged black hole with an annular disk of extremal dust. In order to obtain the solutions, we first solve the Einstein-Maxwell field equations for sources that represent disk-like configurations of matter in confomastatic spacetimes by assuming a functional dependence among the metric function, the electric potential and an auxiliary function,which is taken as a solution of the Laplace equation. We then employ the Lord Kelvin Inversion Method applied to models of finite extension in order to obtain annular disks. The structures obtained extend to infinity, but their total masses are finite and all the energy conditions are satisfied. Finally, we observe that the extremal Reissner-Nordström black hole can be embedded into the center of the disks by adding a boundary term in the inversion.

gr-qc↗

arXiv2010

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.

gr-qc↗

arXiv2010

Numerical solution of the wave equation on particular space-times using CMC slices and scri-fixing conformal compactification

In this paper we present in detail the numerical solution of the conformally invariant wave equation on top of a fixed background space-time corresponding to two different cases: i) 1+1 Minkowski space-time in Cartesian coordinates and ii) Schwarzschild space-time. In both cases we use hyperboloidal constant mean curvature slices and scri-fixing conformal compactification, and solve the wave equation on the conformal space-time. In the case of the Schwarzschild space-time we study the quasinormal mode oscillations and the late-time polynomial tail decay exponents corresponding to a mass-less scalar field. We also present general formulas to construct hyperboloidal constant mean curvature slicings of spherically symmetric, static, space-times in spherical coordinates.

gr-qc↗