Simulations of recoiling black holes: adaptive mesh refinement and radiative transfer

(Abridged) We here continue our effort to model the behaviour of matter when orbiting or accreting onto a generic black hole by developing a new numerical code employing advanced techniques geared solve the equations of in general-relativistic hydrodynamics. The new code employs a number of high-resolution shock-capturing Riemann-solvers and reconstruction algorithms, exploiting the enhanced accuracy and the reduced computational cost of AMR techniques. In addition, the code makes use of sophisticated ray-tracing libraries that, coupled with general-relativistic radiation-transfer calculations, allow us to compute accurately the electromagnetic emissions from such accretion flows. We validate the new code by presenting an extensive series of stationary accretion flows either in spherical or axial symmetry and performed either in 2D or 3D. In addition, we consider the highly nonlinear scenario of a recoiling black hole produced in the merger of a supermassive black hole binary interacting with the surrounding circumbinary disc. In this way we can present, for the first time, ray-traced images of the shocked fluid and the light-curve resulting from consistent general-relativistic radiation-transport calculations from this process. The work presented here lays the ground for the development of a generic computational infrastructure employing AMR techniques to deal accurately and self-consistently with accretion flows onto compact objects. In addition to the accurate handling of the matter, we provide a self-consistent electromagnetic emission from these scenarios by solving the associated radiative-transfer problem. While magnetic fields are presently excluded from our analysis, the tools presented here can have a number of applications to study accretion flows onto black holes or neutron stars.Comment: 20 pages, 20 figures, accepted for publication in A&

Heat sensor on wheels

2018/201

Two-moment scheme for general-relativistic radiation hydrodynamics: a systematic description and new applications

We provide a systematic description of the steps necessary -- and of the potential pitfalls to be encountered -- when implementing a two-moment scheme within an Implicit-Explicit (IMEX) scheme to include radiative-transfer contributions in numerical simulations of general-relativistic (magneto-)hydrodynamics. We make use of the M1 closure, which provides an exact solution for the optically thin and thick limit, and an interpolation between these limits. Special attention is paid to the efficient solution of the emerging set of implicit conservation equations. In particular, we present an efficient method for solving these equations via the inversion of a $4\times 4$-matrix within an IMEX scheme. While this method relies on a few approximations, it offers a very good compromise between accuracy and computational efficiency. After a large number of tests in special relativity, we couple our new radiation code, \texttt{FRAC}, with the general-relativistic magnetohydrodynamics code \texttt{BHAC} to investigate the radiative Michel solution, namely, the problem of spherical accretion onto a black hole in the presence of a radiative field. By performing the most extensive exploration of the parameter space for this problem, we find that the accretion's efficiency can be expressed in terms of physical quantities such as temperature, $T$, luminosity, $L$, and black-hole mass, $M$, via the expression $\varepsilon=(L/L_{\rm Edd})/(\dot{M}/\dot{M}_{\rm Edd})= 7.41\times 10^{-7}\left(T/10^6\,\mathrm{K}\right)^{0.22} \left(L/L_\odot\right)^{0.48} \left(M/M_\odot\right)^{0.48}$, where $L_{\mathrm{Edd}}$ and $\dot{M}_{\mathrm{Edd}}$ are the Eddington luminosity and accretion rate, respectively. Finally, we also consider the accretion problem away from spherical symmetry, finding that the solution is stable under perturbations in the radiation field.Comment: 22 pages, 15 figures, matches version accepted to MNRA

Finanzas : Análisis Financiero aplicado a la empresa Transcarga,S.A.para el periodo terminado 2013-2014

El estudio de las finanzas es muy importante esto por que brinda herramientas muy útil al profesional para desarrollar un análisis del comportamiento operacional de un negocio y para la toma de decisiones que ayuden a enfocarse en el cumplimiento de los objetivos de crecimiento del negocio, esto se realiza en base a la información presentada por la empresa, esta información es mostrada por los estados financieros, la información financiera cumple un rol muy importante al producir datos indispensables para la administración y el desarrollo del sistema económico. Esta investigación es importante porque brinda una situación real de la empresa y así poder servir de apoyo en la tomas de decisiones El presente trabajo se desarrolló con el objetivo de presentar el análisis financieros de la empresa Transcarga S, A para los periodos terminados de los años 2013 y 2014, así como también abordar las generalidades de finanzas y sus herramientas de análisis financieros para poder evaluar la situación financiera de la empresa. El proceso de análisis consiste en la aplicación de un conjunto de técnicas e instrumentos analíticos a los estados financieros para deducir una serie de medidas y relaciones que son significativas y útiles para la toma de decisiones, como resultados del análisis se obtuvieron algunos aspectos que la Empresa presenta algunas dificultades que deben ser resueltas para de esta forma mejorar o transformar positivamente su situación financiera. Entre las razones financieras utilizadas la más significativa es las de liquidez en el año 2014 comparado con los resultados del año 2013, y de igual forma de su Capital de Trabajo, las ventas de la empresa, la cuales presentan una disminución en sus resultados que es un riesgos para la operación de la empresa, en las conclusiones se presenta el comportamiento económico obtenido y los que deberán ser considerados por la gerencia de la empresa

Plasmoid identification and statistics in two-dimensional Harris sheet and GRMHD simulations

Magnetic reconnection is a ubiquitous phenomenon for magnetized plasmas and leads to the rapid reconfiguration of magnetic field lines. During reconnection events, plasma is heated and accelerated until the magnetic field lines enclose and capture the plasma within a circular configuration. These plasmoids could therefore observationally manifest themselves as hot spots that are associated with flaring behavior in supermassive black hole systems, such as Sagittarius A$^\ast$. We have developed a novel algorithm for identifying plasmoid structures, which incorporates watershed and custom closed contouring steps. From the identified plasmoids, we determine the plasma characteristics and energetics in magnetohydrodynamical simulations. The algorithm's performance is showcased for a high-resolution suite of axisymmetric ideal and resistive magnetohydrodynamical simulations of turbulent accretion discs surrounding a supermassive black hole. For validation purposes, we also evaluate several Harris current sheets that are well-investigated in the literature. Interestingly, we recover the characteristic power-law distribution of plasmoid sizes for both the black hole and Harris sheet simulations. This indicates that while the dynamics are vastly different, with different dominant plasma instabilities, the plasmoid creation behavior is similar. Plasmoid occurrence rates for resistive general relativistic magnetohydrodynamical simulations are significantly higher than for the ideal counterpart. Moreover, the largest identified plasmoids are consistent with sizes typically assumed for semi-analytical interpretation of observations. We recover a positive correlation between the plasmoid formation rate and a decrease in black-hole-horizon-penetrating magnetic flux. The developed algorithm has enabled an extensive quantitative analysis of plasmoid formation in black hole accretion simulations.Comment: 23 pages, 15 figures, submitted to MNRA

Tecnología de la información y su relación con la competitividad de una Startup de Comercio Electrónico en Lima – Perú 2023

El presente trabajo de investigación titulado “Tecnología de la información y su relación con la competitividad de una Startup de comercio electrónico en Lima – Perú 2023”, tiene como objetivo general demostrar la influencia de la Tecnología de la información en la competitividad de una Startup de comercio electrónico en Lima – Perú 2023. El diseño del presente trabajo es una investigación de tipo descriptivo, con diseño no experimental de carácter transversal y correlacional. La población para esta investigación, fueron los trabajadores de una Startup de comercio electrónico, la cual totaliza 50 colaboradores. La técnica utilizada fue la encuesta y el instrumento aplicado fue el cuestionario de tipo Likert con 22 preguntas. Este estudio fue trasladado al programa estadístico SPSS para validar el grado de confiabilidad de las variables y la relación que existe entre las mismas, se realizaron tablas estadísticas, gráficos y su respectivo análisis obtenido de la prueba estadística Chi – cuadrado. Terminado el trabajo de investigación pasamos a la conclusiones y recomendaciones

Magnetic flux eruptions at the root of time-lags in low-luminosity AGN

Sagittarius A$^\ast$ is a compact radio source at the center of the Milky Way that has not conclusively shown evidence for the presence of a relativistic jet. Nevertheless, indirect methods at radio frequencies do indicate consistent outflow signatures. Brinkerink et al. (2015) found temporal shifts between frequency bands, called time-lags, which are associated with flares and/or outflows of the accretion system. It is possible to gain information on the emission and potential outflow mechanics by interpreting these time-lags. By means of combined general-relativistic magnetrohydrodynamical and radiative transfer modeling, we study the origin of the time-lags for magnetically arrested disc models at three black hole spins ($a_\ast$ = 0.9375, 0, -0.9375). The study also includes a targeted `slow light' study for one of the best-fitting `fast light' windows. We were able to recover the time-lags found by Brinkerink et al. (2015) in various windows of our simulated lightcurves. The theoretical interpretation of these most-promising time-lag windows is threefold; i) a magnetic flux eruption perturbs the jet-disc boundary and creates a flux tube, ii) the flux tube orbits and creates a clear emission feature, and iii) the flux tube interacts with the jet-disc boundary. The best-fitting windows have an intermediate (i=30$^\circ$/50$^\circ$) inclination and zero-BH-spin. The targeted `slow light' study did not yield better-fitting time-lag results, which indicates that the fast vs. slow light paradign is often not intuitively understood and is likely influential in timing-sensitive studies.Comment: 17 pages, 11 figure

The Current Ability to Test Theories of Gravity with Black Hole Shadows

Our Galactic Center, Sagittarius A* (Sgr A*), is believed to harbour a supermassive black hole (BH), as suggested by observations tracking individual orbiting stars. Upcoming sub-millimetre very-long-baseline-interferometry (VLBI) images of Sgr A* carried out by the Event-Horizon-Telescope Collaboration (EHTC) are expected to provide critical evidence for the existence of this supermassive BH. We assess our present ability to use EHTC images to determine if they correspond to a Kerr BH as predicted by Einstein's theory of general relativity (GR) or to a BH in alternative theories of gravity. To this end, we perform general-relativistic magnetohydrodynamical (GRMHD) simulations and use general-relativistic radiative transfer (GRRT) calculations to generate synthetic shadow images of a magnetised accretion flow onto a Kerr BH. In addition, and for the first time, we perform GRMHD simulations and GRRT calculations for a dilaton BH, which we take as a representative solution of an alternative theory of gravity. Adopting the VLBI configuration from the 2017 EHTC campaign, we find that it could be extremely difficult to distinguish between BHs from different theories of gravity, thus highlighting that great caution is needed when interpreting BH images as tests of GR.Comment: Published in Nature Astronomy on 16.04.18 (including supplementary information); simulations at https://blackholecam.org/telling_bhs_apart

How to tell an accreting boson star from a black hole

The capability of the Event Horizon Telescope (EHT) to image the nearest supermassive black hole candidates at horizon-scale resolutions offers a novel means to study gravity in its strongest regimes and to test different models for these objects. Here, we study the observational appearance at 230 GHz of a surfaceless black hole mimicker, namely a non-rotating boson star, in a scenario consistent with the properties of the accretion flow onto Sgr A*. To this end, we perform general relativistic magnetohydrodynamic simulations followed by general relativistic radiative transfer calculations in the boson star space-time. Synthetic reconstructed images considering realistic astronomical observing conditions show that, despite qualitative similarities, the differences in the appearance of a black hole -- either rotating or not -- and a boson star of the type considered here are large enough to be detectable. These differences arise from dynamical effects directly related to the absence of an event horizon, in particular, the accumulation of matter in the form of a small torus or a spheroidal cloud in the interior of the boson star, and the absence of an evacuated high-magnetization funnel in the polar regions. The mechanism behind these effects is general enough to apply to other horizonless and surfaceless black hole mimickers, strengthening confidence in the ability of the EHT to identify such objects via radio observations.Comment: 16 pages, 12 figures. Published in MNRAS. Adding more information in the form of appendices, and a new simulation of a different boson star model. The conclusions do not chang