arXiv subjects

A. Cruz-Osorio

Publications and source records attributed to A. Cruz-Osorio.

14 recordsLinked to original sources

arXiv2025

Shadow and gravitational lensing produced by the nonlinear accretion of a scalar field onto a black hole

The hypothesis that classical scalar fields could constitute dark matter on galactic and cosmic scales has garnered significant interest. In scenarios where supermassive black holes (SMBHs) form through the accretion of matter onto black hole seeds, a critical question arises: what role does dark matter play in this process? We conduct a numerical investigation into the nonlinear dynamical evolution of black hole shadows and gravitational lensing effects resulting from the accretion of an ultralight, real scalar field onto a non-rotating black hole. The scalar field is minimally coupled to Einstein's gravity, and our simulations focus on wave packets, parameterized by their wave number and width, as they interact with and are accreted by a dynamic black hole. Our results demonstrate significant growth in the apparent horizon, photon ring, and Einstein ring sizes compared to those of a Schwarzschild black hole. These findings suggest that the observed photon ring and black hole shadow in Sgr\,A*, and M87* may be influenced by the gravitational interaction between the black hole and ultralight scalar field dark matter.

gr-qc↗

arXiv2024

Broadband Multi-wavelength Properties of M87 during the 2018 EHT Campaign including a Very High Energy Flaring Episode

The nearby elliptical galaxy M87 contains one of the only two supermassive black holes whose emission surrounding the event horizon has been imaged by the Event Horizon Telescope (EHT). In 2018, more than two dozen multi-wavelength (MWL) facilities (from radio to gamma-ray energies) took part in the second M87 EHT campaign. The goal of this extensive MWL campaign was to better understand the physics of the accreting black hole M87*, the relationship between the inflow and inner jets, and the high-energy particle acceleration. Understanding the complex astrophysics is also a necessary first step towards performing further tests of general relativity. The MWL campaign took place in April 2018, overlapping with the EHT M87* observations. We present a new, contemporaneous spectral energy distribution (SED) ranging from radio to very high energy (VHE) gamma-rays, as well as details of the individual observations and light curves. We also conduct phenomenological modelling to investigate the basic source properties. We present the first VHE gamma-ray flare from M87 detected since 2010. The flux above 350 GeV has more than doubled within a period of about 36 hours. We find that the X-ray flux is enhanced by about a factor of two compared to 2017, while the radio and millimetre core fluxes are consistent between 2017 and 2018. We detect evidence for a monotonically increasing jet position angle that corresponds to variations in the bright spot of the EHT image. Our results show the value of continued MWL monitoring together with precision imaging for addressing the origins of high-energy particle acceleration. While we cannot currently pinpoint the precise location where such acceleration takes place, the new VHE gamma-ray flare already presents a challenge to simple one-zone leptonic emission model approaches, and emphasises the need for combined image and spectral modelling.

astro-ph.HE↗

arXiv2024

Ordered magnetic fields around the 3C 84 central black hole

3C84 is a nearby radio source with a complex total intensity structure, showing linear polarisation and spectral patterns. A detailed investigation of the central engine region necessitates the use of VLBI above the hitherto available maximum frequency of 86GHz. Using ultrahigh resolution VLBI observations at the highest available frequency of 228GHz, we aim to directly detect compact structures and understand the physical conditions in the compact region of 3C84. We used EHT 228GHz observations and, given the limited (u,v)-coverage, applied geometric model fitting to the data. We also employed quasi-simultaneously observed, multi-frequency VLBI data for the source in order to carry out a comprehensive analysis of the core structure. We report the detection of a highly ordered, strong magnetic field around the central, SMBH of 3C84. The brightness temperature analysis suggests that the system is in equipartition. We determined a turnover frequency of $ν_m=(113\pm4)$GHz, a corresponding synchrotron self-absorbed magnetic field of $B_{SSA}=(2.9\pm1.6)$G, and an equipartition magnetic field of $B_{eq}=(5.2\pm0.6)$G. Three components are resolved with the highest fractional polarisation detected for this object ($m_\textrm{net}=(17.0\pm3.9)$%). The positions of the components are compatible with those seen in low-frequency VLBI observations since 2017-2018. We report a steeply negative slope of the spectrum at 228GHz. We used these findings to test models of jet formation, propagation, and Faraday rotation in 3C84. The findings of our investigation into different flow geometries and black hole spins support an advection-dominated accretion flow in a magnetically arrested state around a rapidly rotating supermassive black hole as a model of the jet-launching system in the core of 3C84. However, systematic uncertainties due to the limited (u,v)-coverage, however, cannot be ignored.

astro-ph.HE↗

arXiv2017

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.

astro-ph.HE↗

arXiv2016

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 $ε_{v}$, the black hole spin $a$, the asymptotic Mach number ${\cal M}_{\infty}$ and adiabatic index $Γ$. 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 $a=0.98$ and ${\cal M}_{\infty}=1$, respectively. A kind of flip-flop behavior is found at the early times; nevertheless, the system also reaches a steady state.

astro-ph.HE↗

arXiv2015

Newtonian CAFE: a new ideal MHD code to study the solar atmosphere

We present a new code designed to solve the equations of classical ideal magneto-hydrodynamics (MHD) in three dimensions, submitted to a constant gravitational field. The purpose of the code centers on the analysis of solar phenomena within the photosphere-corona region. We present 1D and 2D standard tests to demonstrate the quality of the numerical results obtained with our code. As solar tests we present the transverse oscillations of Alfvenic pulses in coronal loops using a 2.5D model, and as 3D tests we present the propagation of impulsively generated MHD-gravity waves and vortices in the solar atmosphere. The code is based on high-resolution shock-capturing methods, uses the HLLE flux formula combined with Minmod, MC and WENO5 reconstructors. The divergence free magnetic field constraint is controlled using the Flux Constrained Transport method.

astro-ph.SR↗

arXiv2015

Relativistic Bondi-Hoyle-Lyttleton Accretion onto a Rotating Black-Hole: Density Gradients

In this work, we present, for the first time, a numerical study of the Bondi-Hoyle accretion with density gradients in the fully relativistic regime. In this context, we consider accretion onto a Kerr Black Hole (BH) of a supersonic ideal gas, which has density gradients perpendicular to the relative motion. The set of parameters of interest in this study are the Mach number, M, the spin of the BH, a, and the density-gradient parameter of the gas, ρ . We show that, unlike in the Newtonian case, all the studied cases, especially those with density gradient, approach a stationary flow pattern. To illustrate that the system reaches steady state we calculate the mass and angular momentum accretion rates on a spherical surface located almost at the event horizon. In the particular case of M = 1, ρ = 0.5 and BH spin a = 0.5, we observe a disk-like configuration surrounding the BH. Finally, we present the gas morphology and some of its properties.

astro-ph.HE↗

arXiv2015

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.

gr-qc↗

arXiv2013

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 $p=ρ/3$. We calculate the final mass of a black hole by the integration of the accreted radiation energy density during the leptonic era between $t\sim10^{-4}s$ to $t\sim 10^2s$ after the Big Bang. Our results indicate that small PBHs with initial masses between $10^{-4}$ to $1M_{\odot}$ may grow up to hundreds of solar masses, and thus can be SMBH seeds. On the other hand, PBHs formed at $t\sim 1s$ with initial mass between 900 and $\sim 980M_{\odot}$, by the time $t\sim 100s$ show masses of $10^4$ to $10^6M_{\odot}$ 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.

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↗

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↗

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↗

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↗