General relativistic magnetohydrodynamic simulations of accretion on to Sgr A*: how important are radiative losses?

ABSTRACT Using general relativistic magnetohydrodynamic simulations of accreting black holes, we show that a suitable subtraction of the linear polarization per pixel from total intensity images can enhance the photon ring feature. We find that the photon ring is typically a factor of ≃2 less polarized than the rest of the image. This is due to a combination of plasma and general relativistic effects, as well as magnetic turbulence. When there are no other persistently depolarized image features, adding the subtracted residuals over time results in a sharp image of the photon ring. We show that the method works well for sample, viable GRMHD models of Sgr A* and M87*, where measurements of the photon ring properties would provide new measurements of black hole mass and spin, and potentially allow for tests of the ‘no-hair’ theorem of general relativity.

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How to tell an accreting boson star from a black hole

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1878 ◽

2020 ◽

Vol 497 (1) ◽

pp. 521-535 ◽

Cited By ~ 1

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.

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Status of GRMHD simulations and radiative models of Sgr A*

Proceedings of the International Astronomical Union ◽

10.1017/s174392131601259x ◽

2016 ◽

Vol 11 (S322) ◽

pp. 43-49

Author(s):

Monika Mościbrodzka

Keyword(s):

Black Hole ◽

Galactic Center ◽

Kerr Black Hole ◽

Theoretical Models ◽

Radiative Properties ◽

X Ray ◽

Accretion Flows ◽

General Relativistic ◽

Sgr A ◽

Magnetohydrodynamic Simulations

AbstractThe Galactic center is a perfect laboratory for testing various theoretical models of accretion flows onto a supermassive black hole. Here, I review general relativistic magnetohydrodynamic simulations that were used to model emission from the central object - Sgr A*. These models predict dynamical and radiative properties of hot, magnetized, thick accretion disks with jets around a Kerr black hole. Models are compared to radio-VLBI, mm-VLBI, NIR, and X-ray observations of Sgr A*. I present the recent constrains on the free parameters of the model such as accretion rate onto the black hole, the black hole angular momentum, and orientation of the system with respect to our line of sight.

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3D magnetized jet break-out from neutron-star binary merger ejecta: afterglow emission from the jet and the ejecta

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab115 ◽

2021 ◽

Vol 502 (2) ◽

pp. 1843-1855

Author(s):

Antonios Nathanail ◽

Ramandeep Gill ◽

Oliver Porth ◽

Christian M Fromm ◽

Luciano Rezzolla

Keyword(s):

Neutron Star ◽

Thermal Emission ◽

Opening Angle ◽

Hollow Core ◽

Binary Neutron Star ◽

Vlbi Observations ◽

Superluminal Motion ◽

General Relativistic ◽

Star Binary ◽

Magnetohydrodynamic Simulations

ABSTRACT We perform 3D general-relativistic magnetohydrodynamic simulations to model the jet break-out from the ejecta expected to be produced in a binary neutron-star merger. The structure of the relativistic outflow from the 3D simulation confirms our previous results from 2D simulations, namely, that a relativistic magnetized outflow breaking out from the merger ejecta exhibits a hollow core of θcore ≈ 4°, an opening angle of θjet ≳ 10°, and is accompanied by a wind of ejected matter that will contribute to the kilonova emission. We also compute the non-thermal afterglow emission of the relativistic outflow and fit it to the panchromatic afterglow from GRB170817A, together with the superluminal motion reported from VLBI observations. In this way, we deduce an observer angle of $\theta _{\rm obs}= 35.7^{\circ \, \, +1.8}_{\phantom{\circ \, \, }-2.2}$. We further compute the afterglow emission from the ejected matter and constrain the parameter space for a scenario in which the matter responsible for the thermal kilonova emission will also lead to a non-thermal emission yet to be observed.

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PARSEC-SCALE FARADAY ROTATION MEASURES FROM GENERAL RELATIVISTIC MAGNETOHYDRODYNAMIC SIMULATIONS OF ACTIVE GALACTIC NUCLEUS JETS

The Astrophysical Journal ◽

10.1088/0004-637x/725/1/750 ◽

2010 ◽

Vol 725 (1) ◽

pp. 750-773 ◽

Cited By ~ 60

Author(s):

Avery E. Broderick ◽

Jonathan C. McKinney

Keyword(s):

Faraday Rotation ◽

Active Galactic Nucleus ◽

General Relativistic ◽

Magnetohydrodynamic Simulations

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Plasmoid formation in global GRMHD simulations and AGN flares

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1165 ◽

2020 ◽

Vol 495 (2) ◽

pp. 1549-1565 ◽

Cited By ~ 4

Author(s):

Antonios Nathanail ◽

Christian M Fromm ◽

Oliver Porth ◽

Hector Olivares ◽

Ziri Younsi ◽

...

Keyword(s):

Black Holes ◽

Dipolar Field ◽

Relativistic Jets ◽

Poloidal Magnetic Field ◽

Accretion Flows ◽

Rotating Black Holes ◽

General Relativistic ◽

Formation And Evolution ◽

Magnetohydrodynamic Simulations ◽

Dissipation Processes

ABSTRACT One of the main dissipation processes acting on all scales in relativistic jets is thought to be governed by magnetic reconnection. Such dissipation processes have been studied in idealized environments, such as reconnection layers, which evolve in merging islands and lead to the production of ‘plasmoids’, ultimately resulting in efficient particle acceleration. In accretion flows on to black holes, reconnection layers can be developed and destroyed rapidly during the turbulent evolution of the flow. We present a series of two-dimensional general-relativistic magnetohydrodynamic simulations of tori accreting on to rotating black holes focusing our attention on the formation and evolution of current sheets. Initially, the tori are endowed with a poloidal magnetic field having a multiloop structure along the radial direction and with an alternating polarity. During reconnection processes, plasmoids and plasmoid chains are developed leading to a flaring activity and hence to a variable electromagnetic luminosity. We describe the methods developed to track automatically the plasmoids that are generated and ejected during the simulation, contrasting the behaviour of multiloop initial data with that encountered in typical simulations of accreting black holes having initial dipolar field composed of one loop only. Finally, we discuss the implications that our results have on the variability to be expected in accreting supermassive black holes.

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Accelerating AGN jets to parsec scales using general relativistic MHD simulations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2626 ◽

2019 ◽

Vol 490 (2) ◽

pp. 2200-2218 ◽

Cited By ~ 16

Author(s):

K Chatterjee ◽

M Liska ◽

A Tchekhovskoy ◽

S B Markoff

Keyword(s):

Ambient Medium ◽

Galactic Nuclei ◽

Lorentz Factor ◽

Opening Angle ◽

Long Baseline ◽

General Relativistic ◽

Field Lines ◽

Magnetohydrodynamic Simulations ◽

Jet Collimation ◽

Sheath Structure

ABSTRACT Accreting black holes produce collimated outflows, or jets, that traverse many orders of magnitude in distance, accelerate to relativistic velocities, and collimate into tight opening angles. Of these, perhaps the least understood is jet collimation due to the interaction with the ambient medium. In order to investigate this interaction, we carried out axisymmetric general relativistic magnetohydrodynamic simulations of jets produced by a large accretion disc, spanning over 5 orders of magnitude in time and distance, at an unprecedented resolution. Supported by such a disc, the jet attains a parabolic shape, similar to the M87 galaxy jet, and the product of the Lorentz factor and the jet half-opening angle, γθ ≪ 1, similar to values found from very long baseline interferometry (VLBI) observations of active galactic nuclei (AGNs) jets; this suggests extended discs in AGNs. We find that the interaction between the jet and the ambient medium leads to the development of pinch instabilities, which produce significant radial and lateral variability across the jet by converting magnetic and kinetic energy into heat. Thus pinched regions in the jet can be detectable as radiating hotspots and may provide an ideal site for particle acceleration. Pinching also causes gas from the ambient medium to become squeezed between magnetic field lines in the jet, leading to enhanced mass loading and deceleration of the jet to non-relativistic speeds, potentially contributing to the spine-sheath structure observed in AGN outflows.

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The effects of resolution on black hole accretion simulations of jets

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2423 ◽

2020 ◽

Vol 498 (2) ◽

pp. 2428-2439

Author(s):

Christopher J White ◽

Fiona Chrystal

Keyword(s):

Black Hole ◽

Velocity Structure ◽

Grid Resolution ◽

Black Hole Accretion ◽

General Relativistic ◽

Axisymmetric Structure ◽

Magnetohydrodynamic Simulations ◽

Jet Power ◽

Hole Accretion

ABSTRACT We perform three general-relativistic magnetohydrodynamic simulations of black hole accretion designed to test how sensitive results are to grid resolution in the jet region. The cases differ only in numerics, modelling the same physical scenario of a radiatively inefficient, geometrically thick, magnetically arrested flow on to a rapidly spinning black hole. Properties inferred with the coarsest grid generally agree with those found with higher resolutions, including total jet power and its decomposition into different forms, velocity structure, non-axisymmetric structure, and the appearance of resolved millimetre images. Some measures of variability and magnetization are sensitive to resolution. We conclude that most results obtained by limiting resolution near the jet for computational expediency should still be reliable, at least in so far as they would not be improved with a finer grid.

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

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa099 ◽

2020 ◽

Cited By ~ 5

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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