Testing SgrA<sup>*</sup>with the spectrum of its accretion structure

Lin, Nan; Li, Zilong; Arthur, Jake; Asquith, Rachel; Bambi, Cosimo

doi:10.1088/1475-7516/2015/9/038

Cited by 6 publications

(6 citation statements)

References 52 publications

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“…[416,417] who calculated images and spectra for a toroidal accretion flow around a Kerr black hole in the model of Refs. [445][446][447], Reference [448] calculated spectra for the same torus model in the background of the Kerr-like metric of Ref. [64] and showed that such spectra can depend significantly on deviations from the Kerr metric.…”

Section: The Accretion Flow Of Sgr a *mentioning

confidence: 99%

“…Building on the work of [416,417] who calculated images and spectra for a toroidal accretion flow around a Kerr black hole in the model of [445][446][447][448] calculated spectra for the same torus model in the background of the Kerr-like metric of [64] and showed that such spectra can depend significantly on deviations from the Kerr metric. Figure 30 shows two sets of spectra for different values of the deviation parameter, where the black hole has fixed values of the spin = a r 0.5 g and inclination q =  60 and the torus has fixed values of the specific angular momentum of the fluid particles l = 0.3 or l = 0.6 (shown in the left and right panels, respectively), magnetic to total pressure ratio b = 0.1, electron to ion (corresponding to the maximum of the curve w M ( ), where ω is the frequency of the scalar field; see [449]) and ADM spin = a r 0.80 g using the accretion flow model of [416,417] with a fixed inner radius.…”

Section: The Accretion Flow Of Sgra *mentioning

confidence: 99%

See 1 more Smart Citation

Sgr A* and general relativity

Johannsen¹

2016

Class. Quantum Grav.

142

125

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General relativity has been widely tested in weak gravitational fields but still stands largely untested in the strong-field regime. According to the no-hair theorem, black holes in general relativity depend only on their masses and spins and are described by the Kerr metric. Mass and spin are the first two multipole moments of the Kerr spacetime and completely determine all higher-order moments. The no-hair theorem and, hence, general relativity can be tested by measuring potential deviations from the Kerr metric affecting such higher-order moments. Sagittarius A * (Sgr A * ), the supermassive black hole at the center of the Milky Way, is a prime target for precision tests of general relativity with several experiments across the electromagnetic spectrum. First, near-infrared (NIR) monitoring of stars orbiting around Sgr A * with current and new instruments is expected to resolve their orbital precessions. Second, timing observations of radio pulsars near the Galactic center may detect characteristic residuals induced by the spin and quadrupole moment of Sgr A * . Third, the Event Horizon Telescope, a global network of mm and sub-mm telescopes, aims to study Sgr A * on horizon scales and to image the silhouette of its shadow cast against the surrounding accretion flow using very-long baseline interferometric (VLBI) techniques. Both NIR and VLBI observations may also detect quasiperiodic variability of the emission from the accretion flow of Sgr A * . In this review, I discuss our current understanding of the spacetime of Sgr A * and the prospects of NIR, timing, and VLBI observations to test its Kerr nature in the near future. this regime, it is sufficient to employ a parameterized post-Newtonian framework within which suitable corrections to Newtonian gravity in flat space can be calculated [59]. In the strong-field regime, however, i.e., at radii r ∼ r g , which are targeted by observations of the accretion flow of Sgr A * with the EHT and NIR instruments such as GRAVITY, the parameterized post-Newtonian formalism can no longer be applied. Instead, a careful modeling of the underlying spacetime in terms of a Kerr-like metric (e.g., [60][61][62][63][64][65][66][67][68]) is required.Strong-field tests of general relativity with black holes have also been proposed using gravitationalwave observations of extreme mass-ratio inspirals (EMRIs) [61-63, 65, 69-80] and of gravitational ringdown radiation of perturbed black holes after a merger with another object [81][82][83]. See Refs. [84,85] for recent reviews. Likewise, strong-field tests of general relativity have been suggested using other electromagnetic observations of accretion flows in terms of their continuum spectra [12,68,[86][87][88][89][90][91][92][93][94][95], relativistically-broadened iron lines [93,94,[96][97][98][99][100][101][102][103], variability [101,104-109], X-ray polarization [91,95,110], jets [111], and other accretion properties [12,13,[112][113][114][115][116]. See Ref.[117] for a review.All three approaches to test general relativity with...

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Section: The Accretion Flow Of Sgr a *mentioning

confidence: 99%

Section: The Accretion Flow Of Sgra *mentioning

confidence: 99%

Sgr A* and general relativity

Johannsen¹

2016

Class. Quantum Grav.

142

125

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“…The other goal of the EHT collaboration is the registration of the supermassive black hole M87* with the mass M = (6.6 ± 0.4) × 10 9 M ⊙ in the nearest to us giant elliptical galaxy M87 (NGC 4486), which is placed in the central part of the Virgo cluster of galaxies [93][94][95][96]. The technological levels of the EHT and similar projects BlackHoleCam [97] and GRAVITY [98,99] permit to reach the angular resolution that matches the event horizon size of these supermassive black holes and allow to get the black hole image [100][101][102][103][104][105][106][107][108][109][110][111][112][113].…”

Section: Introductionmentioning

confidence: 99%

Visible shapes of black holes M87* and SgrA*

Dokuchaev,

Nazarova

2020

Preprint

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We review the physical origins for possible visible images of the supermassive black hole M87* in the galaxy M87 and SgrA* in the Milky Way Galaxy. The classical dark black hole shadow of the maximal size is visible in the case of luminous background behind the black hole at the distance exceeding the so-called photon spheres. The notably smaller dark shadow (dark silhouette) of the black hole event horizon is visible if the black hole is highlighted by the inner parts of the luminous accreting matter inside the photon spheres. The first image of the supermassive black hole M87 *, obtained by the Event Horizon Telescope collaboration, shows the lensed dark image of the southern hemisphere of the black hole event horizon globe, highlighted by accreting matter, while the classical black hole shadow is invisible at all. A size of the dark spot on the EHT image agrees with a corresponding size of the dark event horizon silhouette in a thin accretion disk model in the case of either the high or moderate value of the black hole spin, a 0.75. CONTENTS

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“…There is another important diagnostic, namely, the accretion phenomenon around compact objects that has already been a very active field of research (see, e.g., [17][18][19][20][21][22][23][24][25][26][27]). The first comprehensive study of accretion disks using a Newtonian approach was made in [28].…”

Section: Introductionmentioning

confidence: 99%

Accretion disk around the rotating Damour–Solodukhin wormhole

Karimov¹,

Izmailov²,

Nandi³

2019

Eur. Phys. J. C

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A new rotating generalization of the Damour-Solodukhin wormhole (RDSWH), called Kerr-like wormhole, has recently been proposed and investigated by Bueno et al. for echoes in the gravitational wave signal. We show a novel feature of the RDSWH, viz., that the kinematic properties such as the ISCO or marginally stable radius r ms , efficiency and the disk potential V eff are independent of λ (which means they are identical to their KBH counterparts for any given spin). Differences however appear in the emissivity properties for higher values 0.1 < λ ≤ 1 (say) and for the extreme spin a = 0.998. The kinematic and emissivity are generic properties as variations of the wormhole mass and the rate of accretion within the model preserve these properties. Specifically, the behavior of the luminosity peak is quite opposite to each other for the two objects, which could be useful from the viewpoint of observations. Apart from this, an estimate of the difference Δ λ in the maxima of flux of radiation F(r) shows non-zero values but is too tiny to be observable at present for λ < 10 −3 permitted by the strong lensing bound. The broad conclusion is that RDSWH are experimentally indistinguishable from KBH by accretion characteristics.

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Testing SgrA^*with the spectrum of its accretion structure

Cited by 6 publications

References 52 publications

Sgr A* and general relativity

Sgr A* and general relativity

Visible shapes of black holes M87* and SgrA*

Accretion disk around the rotating Damour–Solodukhin wormhole

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Testing SgrA*with the spectrum of its accretion structure

Cited by 6 publications

References 52 publications

Sgr A* and general relativity

Sgr A* and general relativity

Visible shapes of black holes M87* and SgrA*

Accretion disk around the rotating Damour–Solodukhin wormhole

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Product

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Testing SgrA^*with the spectrum of its accretion structure