Toward the event horizon—the supermassive black hole in the Galactic Center

Falcke, H.; Markoff, Sera

doi:10.1088/0264-9381/30/24/244003

Cited by 147 publications

(140 citation statements)

References 198 publications

(303 reference statements)

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“…Several different, partially overlapping data sets exist in the literature. The particular data points we are using here were prepared by Broderick et al (2011a), while a comparable collection of data is available in the more recent review by Falcke & Markoff (2013).…”

Section: Current Spectral and Imagingmentioning

confidence: 99%

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THE POWER OF IMAGING: CONSTRAINING THE PLASMA PROPERTIES OF GRMHD SIMULATIONS USING EHT OBSERVATIONS OF Sgr A*

Chan

Psaltis

Özel

et al. 2015

ApJ

139

162

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Recent advances in general relativistic magnetohydrodynamic simulations have expanded and improved our understanding of the dynamics of black-hole accretion disks. However, current simulations do not capture the thermodynamics of electrons in the low density accreting plasma. This poses a significant challenge in predicting accretion flow images and spectra from first principles. Because of this, simplified emission models have often been used, with widely different configurations (e.g., disk-versus jet-dominated emission), and were able to account for the observed spectral properties of accreting black holes. Exploring the large parameter space introduced by such models, however, requires significant computational power that exceeds conventional computational facilities. In this paper, we use GRay, a fast graphics processing unit (GPU) based ray-tracing algorithm, on the GPU cluster El Gato, to compute images and spectra for a set of six general relativistic magnetohydrodynamic simulations with different magnetic field configurations and black-hole spins. We also employ two different parametric models for the plasma thermodynamics in each of the simulations. We show that, if only the spectral properties of Sgr A * are used, all 12 models tested here can fit the spectra equally well. However, when combined with the measurement of the image size of the emission using the Event Horizon Telescope, current observations rule out all models with strong funnel emission, because the funnels are typically very extended. Our study shows that images of accretion flows with horizon-scale resolution offer a powerful tool in understanding accretion flows around black holes and their thermodynamic properties.

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Section: Current Spectral and Imagingmentioning

confidence: 99%

“…The size of the image of Sgr A * has been measured over many wavelengths, from the radio to the millimeter (see Falcke & Markoff 2013 for a recent review). At most wavelengths, the size measurement is dominated by the blurring of the image caused by interstellar scattering.…”

Section: Current Spectral and Imagingmentioning

confidence: 99%

THE POWER OF IMAGING: CONSTRAINING THE PLASMA PROPERTIES OF GRMHD SIMULATIONS USING EHT OBSERVATIONS OF Sgr A*

Chan

Psaltis

Özel

et al. 2015

ApJ

139

162

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“…At the wavelength of these observations, the mean scattering ellipse is 635 × 310 microarcsec. The best estimate for the Schwarzschild radius based on observational limits on the black hole mass and distance is 1 R S = 10.2±0.5 μas plus systematic errors (Genzel et al 2010;Falcke & Markoff 2013); we adopt a value of 10 μas for this paper. Intrinsic sizes in the major axis are presented in Table 1 and plotted as a function of time delay following the peak of the NIR flare or the UT time for nontriggered observations ( Figure 6).…”

Section: Two-dimensional Structure In the Average Sizementioning

confidence: 99%

“…In the intervening decades, an enormous and varied body of observational work has focused on this source, because although Sgr A* shows only weak activity, its proximity offers the chance to observe the accretion flow without confusion from surrounding material (see reviews in, e.g., Melia & Falcke 2001;Genzel et al 2010;Markoff 2010;Falcke & Markoff 2013). …”

Section: Introductionmentioning

confidence: 99%

The Intrinsic Two-Dimensional Size of Sagittarius A*

Bower

Markoff

Brunthaler

et al. 2014

ApJ

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General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Download date: 12 May 2018The Astrophysical Journal, 790:1 (10pp), 2014 July 20 doi:10.1088/0004-637X/790/1/1 C 2014. The American Astronomical Society. All rights reserved. Printed in the U.S.A. ABSTRACT We report the detection of the two-dimensional structure of the radio source associated with the Galactic Center black hole, Sagittarius A*, obtained from Very Long Baseline Array observations at a wavelength of 7 mm. The intrinsic source is modeled as an elliptical Gaussian with major-axis size 35.4 × 12.6 R S in position angle 95 THE INTRINSIC TWO-DIMENSIONAL SIZE OF SAGITTARIUS A*• east of north. This morphology can be interpreted in the context of both jet and accretion disk models for the radio emission. There is supporting evidence in large angular-scale multi-wavelength observations for both source models for a preferred axis near 95• . We also place a maximum peak-to-peak change of 15% in the intrinsic major-axis size over five different epochs. Three observations were triggered by detection of near infrared (NIR) flares and one was simultaneous with a large X-ray flare detected by NuSTAR. The absence of simultaneous and quasi-simultaneous flares indicates that not all high energy events produce variability at radio wavelengths. This supports the conclusion that NIR and X-ray flares are primarily due to electron excitation and not to an enhanced accretion rate onto the black hole.

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“…spectral line structure [1,2,3] 8 (see also more recent reviews [11,12] on the subject). Another phenomenon, where one really needs a strong gravitational field approach, is simulations of a shadow formation started since [13,14,15,16] (see also calculations of shadows for different cases [17,18,19,20,21,22] and recent reviews on the subject [23,24]). The problem is connected with attempts to resolve the smallest spot at the Galactic Center with VLBI interferometry in mm-band [25].…”

Section: Introductionmentioning

confidence: 99%