scholarly journals Modelling the polarised emission from black holes on event horizon-scales

2020 ◽  
Vol 14 (S342) ◽  
pp. 9-12 ◽  
Author(s):  
Ziri Younsi ◽  
Oliver Porth ◽  
Yosuke Mizuno ◽  
Christian M. Fromm ◽  
Hector Olivares
Keyword(s):  
Black Holes ◽  
Radiative Transfer ◽  
Event Horizon ◽  
Theoretical Description ◽  
Accretion Flow ◽  
Fundamental Properties ◽  
Sagittarius A ◽  
General Relativistic ◽  
Realistic Images ◽  
Insight Into

AbstractUpcoming VLBI observations will resolve nearby supermassive black holes, most notably Sagittarius A* and M87, on event horizon-scales. Recent observations of Sagittarius A* with the Event Horizon Telescope have revealed horizon-scale structure. Accordingly, the detection and measurement of the back hole “shadow” is expected to enable the existence of astrophysical black holes to be verified directly. Although the theoretical description of the shadow is straightforward, its observational appearance is largely determined by the properties of the surrounding accretion flow, which is highly turbulent. We introduce a new polarised general-relativistic radiative transfer code, BHOSS, which accurately solves the equations of polarised radiative transfer in arbitrary strong-gravity environments, providing physically-realistic images of astrophysical black holes on event horizon-scales, as well as also providing insight into the fundamental properties and nature of the surrounding accretion flow environment.

scholarly journals How to tell an accreting boson star from a black hole

2020 ◽  
Vol 497 (1) ◽  
pp. 521-535 ◽  
Author(s):  
Hector Olivares ◽  
Ziri Younsi ◽  
Christian M Fromm ◽  
Mariafelicia De Laurentis ◽  
Oliver Porth ◽  
...  
Keyword(s):  
Black Hole ◽  
Radiative Transfer ◽  
Event Horizon ◽  
Polar Regions ◽  
Radio Observations ◽  
Accretion Flow ◽  
Supermassive Black Hole ◽  
General Relativistic ◽  
Sgr A ◽  
Magnetohydrodynamic Simulations

ABSTRACT 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 on to 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.

scholarly journals The surprisingly small impact of magnetic fields on the inner accretion flow of Sagittarius A* fueled by stellar winds

2019 ◽  
Vol 492 (3) ◽  
pp. 3272-3293 ◽  
Author(s):  
S M Ressler ◽  
E Quataert ◽  
J M Stone
Keyword(s):  
Angular Momentum ◽  
Magnetic Fields ◽  
Event Horizon ◽  
Initial Conditions ◽  
Rotational Instability ◽  
Stellar Winds ◽  
Accretion Flow ◽  
Sagittarius A ◽  
Mhd Simulations ◽  
Sgr A

ABSTRACT We study the flow structure in 3D magnetohydrodynamic (MHD) simulations of accretion on to Sagittarius A* via the magnetized winds of the orbiting Wolf–Rayet stars. These simulations cover over 3 orders of magnitude in radius to reach ≈300 gravitational radii, with only one poorly constrained parameter (the magnetic field in the stellar winds). Even for winds with relatively weak magnetic fields (e.g. plasma β ∼ 106), flux freezing/compression in the inflowing gas amplifies the field to β ∼ few well before it reaches the event horizon. Overall, the dynamics, accretion rate, and spherically averaged flow profiles (e.g. density, velocity) in our MHD simulations are remarkably similar to analogous hydrodynamic simulations. We attribute this to the broad distribution of angular momentum provided by the stellar winds, which sources accretion even absent much angular momentum transport. We find that the magneto-rotational instability is not important because of (i) strong magnetic fields that are amplified by flux freezing/compression, and (ii) the rapid inflow/outflow times of the gas and inefficient radiative cooling preclude circularization. The primary effect of magnetic fields is that they drive a polar outflow that is absent in hydrodynamics. The dynamical state of the accretion flow found in our simulations is unlike the rotationally supported tori used as initial conditions in horizon scale simulations, which could have implications for models being used to interpret Event Horizon Telescope and GRAVITY observations of Sgr A*.

The Biggest Eyes in the Sky: The EHT

2020 ◽  
pp. 177-202
Author(s):  
John W. Moffat
Keyword(s):  
Black Holes ◽  
Event Horizon ◽  
Accretion Disks ◽  
Bright Light ◽  
Supermassive Black Holes ◽  
Western Hemisphere ◽  
Sagittarius A ◽  
Long Baseline ◽  
The Galaxy ◽  
International Event

The international Event Horizon Telescope (EHT) project aims to observe the supermassive black holes at the centers of galaxies, such as Sagittarius A* at the center of the Milky Way and the more distant M87* in the galaxy M87. Using Very-Long-Baseline Interferometry, the project can observe the shadows of the supermassive black holes that block the bright light emitted by their accretion disks. The EHT ties together radio telescopes ranging across the western hemisphere of Earth to create, in effect, a planet-size telescope. The EHT will determine the size of the shadow, which can be compared to the predictions of general relativity and modified gravity theories. The EHT will also observe the physics of the accretion disks surrounding supermassive black holes. These observations can potentially determine whether a black hole event horizon exists.

scholarly journals Event horizon scale emission models for Sagittarius A*

2013 ◽  
Vol 9 (S303) ◽  
pp. 298-302
Author(s):  
J. Dexter
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Event Horizon ◽  
Near Infrared ◽  
Sagittarius A ◽  
Long Baseline ◽  
Black Hole Accretion ◽  
Emission Models ◽  
Infrared Interferometry ◽  
Sgr A

AbstractVery long baseline interferometry observations at millimeter wavelengths have detected source structure in Sgr A* on event horizon scales. Near-infrared interferometry will achieve similar resolution in the next few years. These experiments provide an unprecedented opportunity to explore strong gravity around black holes, but interpreting the data requires physical modeling. I discuss the calculation of images, spectra, and light curves from relativistic MHD simulations of black hole accretion. The models provide an excellent description of current observations, and predict that we may be on the verge of detecting a black hole shadow, which would constitute the first direct evidence for the existence of black holes.

scholarly journals Polarization imaging of M 87 jets by general relativistic radiative transfer calculation based on GRMHD simulations

2020 ◽  
Vol 72 (2) ◽  
Author(s):  
Yuh Tsunetoe ◽  
Shin Mineshige ◽  
Ken Ohsuga ◽  
Tomohisa Kawashima ◽  
Kazunori Akiyama
Keyword(s):  
Magnetic Field ◽  
Black Hole ◽  
Radiative Transfer ◽  
Circular Polarization ◽  
Polarized Light ◽  
Polarization Degree ◽  
Emission Region ◽  
Magnetic Field Direction ◽  
Accretion Flow ◽  
General Relativistic

Abstract The spectacular images of the M 87 black hole taken by the Event Horizon Telescope (EHT) have opened a new era of black hole research. One of the next issues is to take polarization images around the central black hole (BH). Since radio emission is produced by synchrotron process, polarization properties should vividly reflect the magnetic field structures at the jet base and thus provide good information regarding the magnetic mechanism of jet formation. With this kept in mind we perform general relativistic (GR) radiative transfer calculations of polarized light based on the GR magnetohydrodynamic (MHD) simulation data of accretion flow and outflow in M 87, to obtain their linear and circular polarization images in the BH horizon-scale. We found that the linear polarization components originating from the jet base and inner accretion flow should experience Faraday rotation and depolarization when passing through magnetized plasmas around the BH, thus sensitively depending on the BH spin. Through the comparison with total intensity image at $1.3\:$mm by EHT and the polarization degree and the rotation measure (RM) measured at $1.3\:$mm with the Submillimeter Array, the model with the spin parameter of $a=0.9\, M_{\,\mathrm{BH}}$ (with $M_{\,\mathrm{BH}}$ being the BH mass) is favored over other models with $a = 0.5\, M_{\,\mathrm{BH}}$ or $0.99\, M_{\,\mathrm{BH}}$, though we need further systematic studies for confirmation. We also find in low-temperature models a clear ring-like image in the circular polarization map, which arises because of Faraday conversion of the linearly polarized synchrotron emission and is thus indicative of magnetic field direction. This occurs only when the emission region is threaded with well-ordered magnetic fields and hence no clear images are expected in high-temperature disk models, in which disk emission is appreciable. We will be able to elucidate the field configuration through the comparison between the simulated polarization images and future polarimetry with EHT and other VLBI observations.

General Relativistic Radiative Transfer: Emission from Accreting Black Holes in AGN

2006 ◽  
Vol 6 (S1) ◽  
pp. 205-220 ◽  
Author(s):  
Kinwah Wu ◽  
Steven V Fuerst ◽  
Khee-Gan Lee ◽  
Graziella Branduardi-Raymont
Keyword(s):  
Black Holes ◽  
Radiative Transfer ◽  
General Relativistic

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

2017 ◽  
Vol 598 ◽  
pp. A38 ◽  
Author(s):  
Zakaria Meliani ◽  
Yosuke Mizuno ◽  
Hector Olivares ◽  
Oliver Porth ◽  
Luciano Rezzolla ◽  
...  
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Radiative Transfer ◽  
Neutron Stars ◽  
Adaptive Mesh Refinement ◽  
Mesh Refinement ◽  
Adaptive Mesh ◽  
Numerical Code ◽  
Accretion Flows ◽  
General Relativistic

Context. In many astrophysical phenomena, and especially in those that involve the high-energy regimes that always accompany the astronomical phenomenology of black holes and neutron stars, physical conditions that are achieved are extreme in terms of speeds, temperatures, and gravitational fields. In such relativistic regimes, numerical calculations are the only tool to accurately model the dynamics of the flows and the transport of radiation in the accreting matter. Aims. We here continue our effort of modelling the behaviour of matter when it orbits or is accreted onto a generic black hole by developing a new numerical code that employs advanced techniques geared towards solving the equations of general-relativistic hydrodynamics. Methods. More specifically, 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 adaptive mesh-refinement (AMR) techniques. In addition, the code makes use of sophisticated ray-tracing libraries that, coupled with general-relativistic radiation-transfer calculations, allow us to accurately compute the electromagnetic emissions from such accretion flows. Results. We validate the new code by presenting an extensive series of stationary accretion flows either in spherical or axial symmetry that are performed either in two or three spatial dimensions. 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. Conclusions. The work presented here lays the ground for the development of a generic computational infrastructure employing AMR techniques to accurately and self-consistently calculate general-relativistic 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 currently excluded from our analysis, the tools presented here can have a number of applications to study accretion flows onto black holes or neutron stars.

Sign in / Sign up

Export Citation Format

Share Document