scholarly journals Observational signatures of disc and jet misalignment in images of accreting black holes

2020 ◽  
Vol 499 (1) ◽  
pp. 362-378
Author(s):  
K Chatterjee ◽  
Z Younsi ◽  
M Liska ◽  
A Tchekhovskoy ◽  
S B Markoff ◽  
...  
Keyword(s):  
Accretion Disc ◽  
Accretion Discs ◽  
Time Variability ◽  
Noticeable Effect ◽  
Efficient Energy ◽  
Rotation Axes ◽  
General Relativistic ◽  
Extraction Processes ◽  
Relativistic Magnetohydrodynamics ◽  
Tilted Disc

ABSTRACT Black hole (BH) accretion is one of nature’s most efficient energy extraction processes. When gas falls in, a significant fraction of its gravitational binding energy is either converted into radiation or flows outwards in the form of BH-driven jets and disc-driven winds. Recently, the Event Horizon Telescope (EHT), an Earth-sized submillimetre radio interferometer, captured the first images of M87’s BH. These images were analysed and interpreted using general relativistic magnetohydrodynamics (GRMHD) models of accretion discs with rotation axes aligned with the BH spin axis. However, since infalling gas is often insensitive to the BH spin direction, misalignment between accretion disc and BH spin may be a common occurrence in nature. In this work, we use the general relativistic radiative transfer code bhoss to calculate the first synthetic radio images of (highly) tilted disc/jet models generated by our GPU-accelerated GRMHD code h-amr . While the tilt does not have a noticeable effect on the system dynamics beyond a few tens of gravitational radii from the BH, the warping of the disc and jet can imprint observable signatures in EHT images on smaller scales. Comparing the images from our GRMHD models to the 43 and 230 GHz EHT images of M87, we find that M87 may feature a tilted disc/jet system. Further, tilted discs and jets display significant time variability in the 230 GHz flux that can be further tested by longer-duration EHT observations of M87.

ON MAGNETIC SELF-COLLIMATION OF RELATIVISTIC JETS

2010 ◽  
Vol 19 (06) ◽  
pp. 689-694
Author(s):  
N. GLOBUS ◽  
V. CAYATTE ◽  
C. SAUTY
Keyword(s):  
Black Hole ◽  
Total Energy ◽  
Ideal Fluid ◽  
Polar Axis ◽  
Kerr Metric ◽  
Relativistic Jets ◽  
Simple Criterion ◽  
General Relativistic ◽  
Time Splitting ◽  
Relativistic Magnetohydrodynamics

We present a semi-analytical model using the equations of general relativistic magnetohydrodynamics (GRMHD) for jets emitted by a rotating black hole. We assume steady axisymmetric outflows of a relativistic ideal fluid in Kerr metrics. We express the conservation equations in the frame of the FIDucial Observer (FIDO or ZAMO) using a 3+1 space–time splitting. Calculating the total energy variation between a non-polar field line and the polar axis, we extend to the Kerr metric the simple criterion for the magnetic collimation of jets obtained for a nonrotating black hole by Meliani et al.10 We show that the black role rotation induced a more efficient magnetic collimation of the jet.

scholarly journals Spectral and polarization properties of black hole accretion disc emission: including absorption effects

2020 ◽  
Author(s):  
R Taverna ◽  
L Marra ◽  
S Bianchi ◽  
M Dovčiak ◽  
R Goosmann ◽  
...  
Keyword(s):  
Black Hole ◽  
Polarization State ◽  
General Rule ◽  
Accretion Disc ◽  
Accretion Discs ◽  
Polarization Degree ◽  
Monte Carlo Code ◽  
Black Hole Spin ◽  
Black Hole Accretion ◽  
Hole Accretion

Abstract The study of radiation emitted from black hole accretion discs represents a crucial way to understand the main physical properties of these sources, and in particular the black hole spin. Beside spectral analysis, polarimetry is becoming more and more important, motivated by the development of new techniques which will soon allow to perform measurements also in the X- and γ-rays. Photons emitted from black hole accretion discs in the soft state are indeed expected to be polarized, with an energy dependence which can provide an estimate of the black hole spin. Calculations performed so far, however, considered scattering as the only process to determine the polarization state of the emitted radiation, implicitly assuming that the temperatures involved are such that material in the disc is entirely ionized. In this work we generalize the problem by calculating the ionization structure of a surface layer of the disc with the public code cloudy, and then by determining the polarization properties of the emerging radiation using the Monte Carlo code stokes. This allows us to account for absorption effects alongside scattering ones. We show that including absorption can deeply modify the polarization properties of the emerging radiation with respect to what is obtained in the pure-scattering limit. As a general rule, we find that the polarization degree is larger when absorption is more important, which occurs e.g. for low accretion rates and/or spins when the ionization of the matter in the innermost accretion disc regions is far from complete.

scholarly journals iharm3D: Vectorized General Relativistic Magnetohydrodynamics

2021 ◽  
Vol 6 (66) ◽  
pp. 3336
Author(s):  
Ben Prather ◽  
George Wong ◽  
Vedant Dhruv ◽  
Benjamin Ryan ◽  
Joshua Dolence ◽  
...  
Keyword(s):  
General Relativistic ◽  
Relativistic Magnetohydrodynamics

scholarly journals X-ray Dips in AGN and Microquasars – Collapse Timescales of Inner Accretion Disc

2020 ◽  
Author(s):  
Mayur B Shende ◽  
Prashali Chauhan ◽  
Prasad Subramanian
Keyword(s):  
Collisionless Plasma ◽  
Cosmic Ray ◽  
Outer Radius ◽  
Accretion Disc ◽  
Accretion Discs ◽  
X Rays ◽  
Temporal Behaviour ◽  
X Ray ◽  
Ray Diffusion ◽  
3C 120

Abstract The temporal behaviour of X-rays from some AGN and microquasars is thought to arise from the rapid collapse of the hot, inner parts of their accretion discs. The collapse can occur over the radial infall timescale of the inner accretion disc. However, estimates of this timescale are hindered by a lack of knowledge of the operative viscosity in the collisionless plasma comprising the inner disc. We use published simulation results for cosmic ray diffusion through turbulent magnetic fields to arrive at a viscosity prescription appropriate to hot accretion discs. We construct simplified disc models using this viscosity prescription and estimate disc collapse timescales for 3C 120, 3C 111, and GRS 1915+105. The Shakura-Sunyaev α parameter resulting from our model ranges from 0.02 to 0.08. Our inner disc collapse timescale estimates agree well with those of the observed X-ray dips. We find that the collapse timescale is most sensitive to the outer radius of the hot accretion disc.

scholarly journals Magnetohydrodynamic Turbulence in Accretion Discs: Towards More Realistic Models

1997 ◽  
Vol 163 ◽  
pp. 210-214
Author(s):  
Ulf Torkelsson ◽  
Axel Brandenburg ◽  
Åke Nordlund ◽  
Robert F. Stein
Keyword(s):  
Angular Momentum ◽  
Boundary Conditions ◽  
Accretion Disc ◽  
Quantitative Change ◽  
Accretion Discs ◽  
Momentum Transport ◽  
Magnetohydrodynamic Turbulence ◽  
Accretion Flow ◽  
Angular Momentum Transport ◽  
Main Effects

AbstractThe shearing box has rapidly become the accepted way to investigate turbulence in Keplerian shear flows. In this paper we discuss to what extent and in which way the outcome of the shearing box is affected by the adopted boundary conditions, and how the shearing box can be modified to capture more of the physics of an accretion disc. The original shearing box model is too symmetric to generate a net accretion flow, but the symmetry can be broken by including the main effects of the cylindrical geometry of the real disc. However the quantitative change in the resulting angular momentum transport is small.

scholarly journals X-rays from Photoionized Accretion Discs

1994 ◽  
Vol 159 ◽  
pp. 380-380
Author(s):  
G. Matt ◽  
A.C. Fabian ◽  
R.R. Ross
Keyword(s):  
Black Hole ◽  
Seyfert Galaxies ◽  
High Energy ◽  
Accretion Disc ◽  
Accretion Discs ◽  
X Rays ◽  
Central Black Hole ◽  
X Ray

The presence of iron lines and high energy excesses in the X-ray spectra of Seyfert galaxies has been firmly established by Ginga (e.g. Nandra & Pounds 1993 and references therein). These features are generally interpreted as signatures of the reprocessing of the primary X-rays by matter in the neighbourhood of the central black hole, probably distributed in an accretion disc (Lightman & White 1988, George & Fabian 1991, Matt, Perola & Piro 1991).

scholarly journals Barycentric interpolation on Riemannian and semi-Riemannian spaces

2019 ◽  
Vol 489 (3) ◽  
pp. 4161-4169
Author(s):  
Pauli Pihajoki ◽  
Matias Mannerkoski ◽  
Peter H Johansson
Keyword(s):  
Interpolation Method ◽  
Arbitrary Dimension ◽  
Curvilinear Coordinates ◽  
Barycentric Coordinates ◽  
Intrinsic Variability ◽  
Curvature Effects ◽  
Barycentric Interpolation ◽  
General Relativistic ◽  
Relativistic Magnetohydrodynamics ◽  
Riemannian Spaces

ABSTRACT Interpolation of data represented in curvilinear coordinates and possibly having some non-trivial, typically Riemannian or semi-Riemannian geometry is a ubiquitous task in all of physics. In this work, we present a covariant generalization of the barycentric coordinates and the barycentric interpolation method for Riemannian and semi-Riemannian spaces of arbitrary dimension. We show that our new method preserves the linear accuracy property of barycentric interpolation in a coordinate-invariant sense. In addition, we show how the method can be used to interpolate constrained quantities so that the given constraint is automatically respected. We showcase the method with two astrophysics related examples situated in the curved Kerr space–time. The first problem is interpolating a locally constant vector field, in which case curvature effects are expected to be maximally important. The second example is a general relativistic magnetohydrodynamics simulation of a turbulent accretion flow around a black hole, wherein high intrinsic variability is expected to be at least as important as curvature effects.

scholarly journals Disc Tearing and Bardeen-Petterson Alignment in GRMHD Simulations of Highly Tilted Thin Accretion Discs

2020 ◽  
Author(s):  
M Liska ◽  
C Hesp ◽  
A Tchekhovskoy ◽  
A Ingram ◽  
M van der Klis ◽  
...  
Keyword(s):  
Black Hole ◽  
Galactic Nuclei ◽  
Accretion Discs ◽  
Emission Model ◽  
Sharp Drop ◽  
Frame Dragging ◽  
General Relativistic ◽  
Magnetohydrodynamic Simulations ◽  
Future Work ◽  
X Ray Binaries

Abstract Luminous active galactic nuclei (AGN) and X-Ray binaries (XRBs) often contain geometrically thin, radiatively cooled accretion discs. According to theory, these are – in many cases – initially highly misaligned with the black hole equator. In this work, we present the first general relativistic magnetohydrodynamic simulations of very thin (h/r∼0.015-0.05) accretion discs around rapidly spinning (a∼0.9) black holes and tilted by 45-65 degrees. We show that the inner regions of the discs with h/r≲0.03 align with the black hole equator, though out to smaller radii than predicted by analytic work. The inner aligned and outer misaligned disc regions are separated by a sharp break in tilt angle accompanied by a sharp drop in density. We find that frame-dragging by the spinning black hole overpowers the disc viscosity, which is self-consistently produced by magnetized turbulence, tearing the disc apart and forming a rapidly precessing inner sub-disc surrounded by a slowly precessing outer sub-disc. We find that the system produces a pair of relativistic jets for all initial tilt values. At small distances the black hole launched jets precess rapidly together with the inner sub-disc, whereas at large distances they partially align with the outer sub-disc and precess more slowly. If the tearing radius can be modeled accurately in future work, emission model independent measurements of black hole spin based on precession-driven quasi-periodic oscillations may become possible.

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