scholarly journals Flares in the Galactic Centre – I. Orbiting flux tubes in magnetically arrested black hole accretion discs

2021 ◽  
Vol 502 (2) ◽  
pp. 2023-2032
Author(s):  
O Porth ◽  
Y Mizuno ◽  
Z Younsi ◽  
C M Fromm
Keyword(s):  
Black Hole ◽  
Magnetic Energy ◽  
Gravity Data ◽  
Accretion Discs ◽  
Galactic Centre ◽  
Flux Tubes ◽  
Black Hole Accretion ◽  
General Relativistic ◽  
Sgr A ◽  
The Magnetic Field

ABSTRACT Recent observations of Sgr A* by the GRAVITY instrument have astrometrically tracked infrared (IR) flares at distances of ∼10 gravitational radii (rg). In this paper, we study a model for the flares based on 3D general relativistic magnetohydrodynamic (GRMHD) simulations of magnetically arrested accretion discs (MADs) that exhibit violent episodes of flux escape from the black hole magnetosphere. These events are attractive for flare modelling for several reasons: (i) the magnetically dominant regions can resist being disrupted via magnetorotational turbulence and shear; (ii) the orientation of the magnetic field is predominantly vertical as suggested by the GRAVITY data; and (iii) the magnetic reconnection associated with the flux eruptions could yield a self-consistent means of particle heating/acceleration during the flare events. In this analysis, we track erupted flux bundles and provide distributions of sizes, energies, and plasma parameter. In our simulations, the orbits tend to circularize at a range of radii from ${\sim} 5\hbox{ to }40\, r_{\rm g}$. The magnetic energy contained within the flux bundles ranges up to ${\sim} 10^{40}\,\rm erg$, enough to power IR and X-ray flares. We find that the motion within the magnetically supported flow is substantially sub-Keplerian, in tension with the inferred period–radius relation of the three GRAVITY flares.

scholarly journals heroic: 3D general relativistic radiative post-processor with comptonization for black hole accretion discs

2016 ◽  
Vol 457 (1) ◽  
pp. 608-628 ◽  
Author(s):  
Ramesh Narayan ◽  
Yucong Zhu ◽  
Dimitrios Psaltis ◽  
Aleksander Sa̧dowski
Keyword(s):  
Black Hole ◽  
Accretion Discs ◽  
Black Hole Accretion ◽  
General Relativistic ◽  
Hole Accretion

scholarly journals Blob formation and ejection from the radiative inefficient accretion flow around massive black hole

2020 ◽  
Author(s):  
Tian-Le Zhao ◽  
Ye-Fei Yuan ◽  
Rajiv Kumar
Keyword(s):  
Magnetic Field ◽  
Black Hole ◽  
Current Sheet ◽  
Magnetic Energy ◽  
Small Scale ◽  
Central Black Hole ◽  
Massive Black Hole ◽  
Accretion Flow ◽  
Black Hole Accretion ◽  
Sgr A

Abstract We study the small scale magnetic reconnection above the radiative inefficient accretion flow around massive black hole via 2D magnetohydrodynamics (MHD) numerical simulation, in order to model the blob formation and ejection from the accretion flow around Sgr A*. The connection of both the newly emerging magnetic field and the pre-existing magnetic field is investigated to check whether blobs could be driven in the environment of black hole accretion disk. After the magnetic connection, both the velocity and temperature of the plasma can be comparable to the inferred physical properties at the base of the observed blob ejection. For illustration, three small boxes which are located within 40 Schwarzschild radii from the central black hole are chosen as our simulation areas. At the beginning of the reconnections, the fluid is pulled toward the central black hole due to the gravitational attraction, and the current sheet produced by the reconnection is also pulled toward the same direction, consequently, the resulting outflows move both upward and toward the symmetry axis of the central black hole. Eventually, huge blobs appear, which supports the catastrophe model of episodic jets (Yuan et al. 2009a). It is also found that the closer to the black hole the magnetic connection happens, the higher the converting efficiency of the magnetic energy into the heat and kinetic energy. For these inner blobs, they have vortex structure due to the Kelvin-Helmholtz instability which happens along the current sheet separating the fluids with different speed.

scholarly journals Detection of the gravitational redshift in the orbit of the star S2 near the Galactic centre massive black hole

2018 ◽  
Vol 615 ◽  
pp. L15 ◽  
Author(s):  
◽  
R. Abuter ◽  
A. Amorim ◽  
N. Anugu ◽  
M. Bauböck ◽  
...  
Keyword(s):  
Black Hole ◽  
Adaptive Optics ◽  
Gravitational Redshift ◽  
Galactic Centre ◽  
Order Effects ◽  
Massive Black Hole ◽  
Black Hole Candidate ◽  
Very Large Telescope ◽  
General Relativistic ◽  
Sgr A

The highly elliptical, 16-year-period orbit of the star S2 around the massive black hole candidate Sgr A✻ is a sensitive probe of the gravitational field in the Galactic centre. Near pericentre at 120 AU ≈ 1400 Schwarzschild radii, the star has an orbital speed of ≈7650 km s−1, such that the first-order effects of Special and General Relativity have now become detectable with current capabilities. Over the past 26 years, we have monitored the radial velocity and motion on the sky of S2, mainly with the SINFONI and NACO adaptive optics instruments on the ESO Very Large Telescope, and since 2016 and leading up to the pericentre approach in May 2018, with the four-telescope interferometric beam-combiner instrument GRAVITY. From data up to and including pericentre, we robustly detect the combined gravitational redshift and relativistic transverse Doppler effect for S2 of z = Δλ / λ ≈ 200 km s−1/c with different statistical analysis methods. When parameterising the post-Newtonian contribution from these effects by a factor f , with f = 0 and f = 1 corresponding to the Newtonian and general relativistic limits, respectively, we find from posterior fitting with different weighting schemes f = 0.90 ± 0.09|stat ± 0.15|sys. The S2 data are inconsistent with pure Newtonian dynamics.

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 Black hole accretion discs and screened scalar hair

2016 ◽  
Vol 2016 (10) ◽  
pp. 024-024 ◽  
Author(s):  
Anne-Christine Davis ◽  
Ruth Gregory ◽  
Rahul Jha
Keyword(s):  
Black Hole ◽  
Accretion Discs ◽  
Black Hole Accretion ◽  
Scalar Hair ◽  
Hole Accretion

scholarly journals Relative depolarization of the black hole photon ring in GRMHD models of Sgr A* and M87*

2021 ◽  
Vol 503 (3) ◽  
pp. 4563-4575
Author(s):  
A Jiménez-Rosales ◽  
J Dexter ◽  
S M Ressler ◽  
A Tchekhovskoy ◽  
M Bauböck ◽  
...  
Keyword(s):  
Black Hole ◽  
Relativistic Effects ◽  
Image Features ◽  
Black Hole Mass ◽  
Magnetic Turbulence ◽  
Intensity Images ◽  
General Relativistic ◽  
Sharp Image ◽  
Sgr A ◽  
Magnetohydrodynamic Simulations

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.

scholarly journals Detection of the Schwarzschild precession in the orbit of the star S2 near the Galactic centre massive black hole

2020 ◽  
Vol 636 ◽  
pp. L5 ◽  
Author(s):  
◽  
R. Abuter ◽  
A. Amorim ◽  
M. Bauböck ◽  
J. P. Berger ◽  
...  
Keyword(s):  
Black Hole ◽  
Reference Frame ◽  
Adaptive Optics ◽  
Galactic Centre ◽  
Massive Black Hole ◽  
Central Mass ◽  
Black Hole Candidate ◽  
Beam Combiner ◽  
Direct Measurements ◽  
Sgr A

The star S2 orbiting the compact radio source Sgr A* is a precision probe of the gravitational field around the closest massive black hole (candidate). Over the last 2.7 decades we have monitored the star’s radial velocity and motion on the sky, mainly with the SINFONI and NACO adaptive optics (AO) instruments on the ESO VLT, and since 2017, with the four-telescope interferometric beam combiner instrument GRAVITY. In this Letter we report the first detection of the General Relativity (GR) Schwarzschild Precession (SP) in S2’s orbit. Owing to its highly elliptical orbit (e = 0.88), S2’s SP is mainly a kink between the pre-and post-pericentre directions of motion ≈±1 year around pericentre passage, relative to the corresponding Kepler orbit. The superb 2017−2019 astrometry of GRAVITY defines the pericentre passage and outgoing direction. The incoming direction is anchored by 118 NACO-AO measurements of S2’s position in the infrared reference frame, with an additional 75 direct measurements of the S2-Sgr A* separation during bright states (“flares”) of Sgr A*. Our 14-parameter model fits for the distance, central mass, the position and motion of the reference frame of the AO astrometry relative to the mass, the six parameters of the orbit, as well as a dimensionless parameter fSP for the SP (fSP = 0 for Newton and 1 for GR). From data up to the end of 2019 we robustly detect the SP of S2, δϕ ≈ 12′ per orbital period. From posterior fitting and MCMC Bayesian analysis with different weighting schemes and bootstrapping we find fSP = 1.10 ± 0.19. The S2 data are fully consistent with GR. Any extended mass inside S2’s orbit cannot exceed ≈0.1% of the central mass. Any compact third mass inside the central arcsecond must be less than about 1000 M⊙.

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