Search results for "black hole"
showing 10 items of 336 documents
Shock oscillation model for quasi-periodic oscillations in stellar mass and supermassive black holes
2007
We numerically examine centrifugally supported shock waves in 2D rotating accretion flows around a stellar-mass (10M_sun) and a supermassive (10^6M_sun) black holes over a wide range of input accretion rates of 10^7 >\dot M/\dot M_E>10^{-4}. The resultant 2D-shocks are unstable with time and the luminosities show quasi-periodic oscillations (QPOs) with modulations of a factor of 2-3 andwith periods of a tenth seconds to several hours, depending on the black hole masses. The shock oscillation model may explain the intermediate frequency QPOs with 1-10 Hz observed in the stellar-mass black hole candidates and also suggest the existence of QPOs with the period of hours in AGNs. When the accret…
A quantum model of Schwarzschild black hole evaporation
1996
We construct a one-loop effective metric describing the evaporation phase of a Schwarzschild black hole in a spherically symmetric null-dust model. This is achieved by quantising the Vaidya solution and by chosing a time dependent quantum state. This state describes a black hole which is initially in thermal equilibrium and then the equilibrium is switched off, so that the black hole starts to evaporate, shrinking to a zero radius in a finite proper time. The naked singularity appears, and the Hawking flux diverges at the end-point. However, a static metric can be imposed in the future of the end-point. Although this end-state metric cannot be determined within our construction, we show tha…
Symmetries and solvable models for evaporating 2D black holes
1997
We study the evaporation process of a 2D black hole in thermal equilibrium when the ingoing radiation is suddenly switched off. We also introduce global symmetries of generic 2D dilaton gravity models which generalize the extra symmetry of the CGHS model. © Elsevier Science B.V
Dynamics in the Magnetospheres of Compact Objects
2020
Esta tesis doctoral explora el modelado de la dinámica en las magnetosferas alrededor de objetos compactos (agujeros negros y estrellas de neutrones), y sus implicaciones en la formación de fenómenos de alta energía como las llamaradas en magnetares y la emisión de alta variabilidad en el rango de los teraelectronvoltios (TeV) de algunos núcleos galácticos activos, por medio de simulaciones numéricas. Las sorprendentes imágenes de las sombras de los agujeros negros (BH) del centro galáctico y la galaxia M87 proporcionan una primera visión directa de la física de los flujos de acreción en los entornos más extremos del universo. La extracción eficiente de energía en forma de flujos de plasma …
Science case study and scientific simulations for the enhanced X-ray Timing Polarimetry mission, eXTP
2022
The X-ray astronomy mission eXTP (enhanced X-ray Timing Polarimetry) is designed to study matter under extreme conditions of density, gravity and magnetism. Primary goals are the determination of the equation of state (EoS) of matter at supranuclear density, the physics in extremely strong magnetic fields, the study of accretion in strong-field gravity (SFG) regime. Primary targets include isolated and binary neutron stars, strong magneticfield systems like magnetars, and stellar-mass and supermassive black holes. In this paper we report about key observations and simulations with eXTP on the primary objectives involving accretion under SFG regimes and determination of NS-EoS.
Tracking the evolution of the accretion flow in MAXI J1820+070 during its hard state with the JED-SAD model
2021
X-ray binaries in outburst typically show two canonical X-ray spectral states, i.e. hard and soft states, in which the physical properties of the accretion flow and of the jet are known to change. Recently, the JED-SAD paradigm has been proposed for black hole X-ray binaries, aimed to address the accretion-ejection interplay in these systems. According to this model, the accretion flow is composed by an outer standard Shakura-Sunyaev disk (SAD) and an inner hot Jet Emitting Disk (JED). The JED produces both the hard X-ray emission, effectively playing the role of the hot corona, and the radio jets. In this paper, we use the JED-SAD model to describe the evolution of the accretion flow in th…
GW170814: A Three-Detector Observation of Gravitational Waves from a Binary Black Hole Coalescence
2017
On August 14, 2017 at 10 30:43 UTC, the Advanced Virgo detector and the two Advanced LIGO detectors coherently observed a transient gravitational-wave signal produced by the coalescence of two stellar mass black holes, with a false-alarm rate of 1 in 27 000 years. The signal was observed with a three-detector network matched-filter signal-to-noise ratio of 18. The inferred masses of the initial black holes are 30.5-3.0+5.7M and 25.3-4.2+2.8M (at the 90% credible level). The luminosity distance of the source is 540-210+130 Mpc, corresponding to a redshift of z=0.11-0.04+0.03. A network of three detectors improves the sky localization of the source, reducing the area of the 90% credible regio…
The 30 Year Search for the Compact Object in SN 1987A
2018
Despite more than 30 years of searches, the compact object in Supernova (SN) 1987A has not yet been detected. We present new limits on the compact object in SN 1987A using millimeter, near-infrared, optical, ultraviolet, and X-ray observations from ALMA, VLT, HST, and Chandra. The limits are approximately 0.1 mJy ($0.1\times 10^{-26}$ erg s$^{-1}$ cm$^{-2}$ Hz$^{-1}$) at 213 GHz, 1 Lsun ($6\times 10^{-29}$ erg s$^{-1}$ cm$^{-2}$ Hz$^{-1}$) in optical if our line-of-sight is free of ejecta dust, and $10^{36}$ erg s$^{-1}$ ($2\times 10^{-30}$ erg s$^{-1}$ cm$^{-2}$ Hz$^{-1}$) in 2-10 keV X-rays. Our X-ray limits are an order of magnitude less constraining than previous limits because we use a…
VLBA polarimetric monitoring of 3C 111
2018
Context. While studies of large samples of jets of active galactic nuclei (AGN) are important in order to establish a global picture, dedicated single-source studies are an invaluable tool for probing crucial processes within jets on parsec scales. These processes involve in particular the formation and geometry of the jet magnetic field as well as the flow itself. Aims. We aim to better understand the dynamics within relativistic magneto-hydrodynamical flows in the extreme environment and close vicinity of supermassive black holes. Methods. We analyze the peculiar radio galaxy 3C 111, for which long-Term polarimetric observations are available. We make use of the high spatial resolution of…
Astronomy and space on the big screen : how accurately has cinema portrayed space travel and other astrophysical concepts?
2016
"Since its origins, cinema has been fascinated with the subject of scientific developments. In particular, astronomy and astrophysics have played an important role in science fiction stories about space travel and exploration. Though the science has not always been accurately represented, in the last decades there has been more and more interest from the cinema industry in approaching scientists to make sure that the stories and concepts shown in films are closer to our true understanding of the universe. In this article, I will explore how cinema has portrayed astrophysical concepts throughout the decades, and how sometimes cinema has even inspired the direction of scientific research."