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Johannsen, Tim; Broderick, Avery E.; Plewa, P. M.; Chatzopoulos, S.; Doeleman, Sheperd S.; Eisenhauer, F.; Fish, Vincent L.; Genzel, R.; Gerhard, Ortwin; Johnson, Michael D.

doi:10.1103/physrevlett.116.031101

Cited by 168 publications

(152 citation statements)

References 58 publications

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“…It is probable that an algorithm (see e.g. [43,45]) trying to detect a Kerr BH shadow on an image similar to the left panel of Fig. 8 would not converge because there is nowhere in the image a photon-ring-like structure: there is no edge (i.e.…”

Section: Fig 5 Configuration I Images Upper Panel: Image At 230mentioning

confidence: 99%

Astrophysical imaging of Kerr black holes with scalar hair

et al. 2016

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We address the astrophysical imaging of a family of deformed Kerr black holes (BHs). These are stationary, asymptotically flat BH spacetimes that are solutions of general relativity minimally coupled to a massive, complex scalar field: Kerr BHs with scalar hair (KBHsSH). Such BHs bifurcate from the vacuum Kerr solution and can be regarded as a horizon within a rotating boson star. In a recent letter [P. V. P. Cunha, C. A. R. Herdeiro, E. Radu, and H. F. Rúnarsson, Phys. Rev. Lett. 115, 211102 (2015).], it was shown that KBHsSH can exhibit very distinct shadows from the ones of their vacuum counterparts. The setup therein, however, considers the light source to be a celestial sphere sufficiently far away from the BH. Here, we analyze KBHsSH surrounded by an emitting torus of matter simulating a more realistic astrophysical environment, and study the corresponding lensing of light as seen by a very faraway observer, to appropriately model ground-based observations of Sgr A Ã . We find that the differences in imaging between KBHsSH and comparable vacuum Kerr BHs remain, albeit less dramatic than those observed for the corresponding shadows in the previous setup. In particular, we highlight two observables that might allow differentiating KBHsSH and Kerr BHs. The first is the angular size of the photon ring (in a Kerr spacetime) or lensing ring (in a KBHSH spacetime), the latter being significantly smaller for sufficiently non-Kerr-like spacetimes. The second is the existence of an edge in the intensity distribution (the photon ring in Kerr spacetime). This edge can disappear for very non-Kerr-like KBHsSH. It is plausible, therefore, that sufficiently precise very long baseline interferometric observations of BH candidates can constrain this model.

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Section: Fig 5 Configuration I Images Upper Panel: Image At 230mentioning

confidence: 99%

Astrophysical imaging of Kerr black holes with scalar hair

et al. 2016

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“…Ref. 89 used a simulated one-day observing EHT run with seven antennas, and demonstrated that the radius of the shadow of Sgr A* can be measured to an accuracy of ∼1.5 µas (corresponding to 6%). Ref.…”

Section: Shadow Measurement Accuracy and Interferometric Simulationsmentioning

confidence: 99%

BlackHoleCam: Fundamental physics of the galactic center

Goddi

Falcke

Krämer

et al. 2017

Int. J. Mod. Phys. D

180

133

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Einstein’s General theory of relativity (GR) successfully describes gravity. Although GR has been accurately tested in weak gravitational fields, it remains largely untested in the general strong field cases. One of the most fundamental predictions of GR is the existence of black holes (BHs). After the recent direct detection of gravitational waves by LIGO, there is now near conclusive evidence for the existence of stellar-mass BHs. In spite of this exciting discovery, there is not yet direct evidence of the existence of BHs using astronomical observations in the electromagnetic spectrum. Are BHs observable astrophysical objects? Does GR hold in its most extreme limit or are alternatives needed? The prime target to address these fundamental questions is in the center of our own Milky Way, which hosts the closest and best-constrained supermassive BH candidate in the universe, Sagittarius A* (Sgr A*). Three different types of experiments hold the promise to test GR in a strong-field regime using observations of Sgr A* with new-generation instruments. The first experiment consists of making a standard astronomical image of the synchrotron emission from the relativistic plasma accreting onto Sgr A*. This emission forms a “shadow” around the event horizon cast against the background, whose predicted size ([Formula: see text]as) can now be resolved by upcoming very long baseline radio interferometry experiments at mm-waves such as the event horizon telescope (EHT). The second experiment aims to monitor stars orbiting Sgr A* with the next-generation near-infrared (NIR) interferometer GRAVITY at the very large telescope (VLT). The third experiment aims to detect and study a radio pulsar in tight orbit about Sgr A* using radio telescopes (including the Atacama large millimeter array or ALMA). The BlackHoleCam project exploits the synergy between these three different techniques and contributes directly to them at different levels. These efforts will eventually enable us to measure fundamental BH parameters (mass, spin, and quadrupole moment) with sufficiently high precision to provide fundamental tests of GR (e.g. testing the no-hair theorem) and probe the spacetime around a BH in any metric theory of gravity. Here, we review our current knowledge of the physical properties of Sgr A* as well as the current status of such experimental efforts towards imaging the event horizon, measuring stellar orbits, and timing pulsars around Sgr A*. We conclude that the Galactic center provides a unique fundamental-physics laboratory for experimental tests of BH accretion and theories of gravity in their most extreme limits.

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“…Other models such as the Kerr black hole with scalar hair predict shadows of distinguishable shape from those in general relativity [14]. Differentiability of shadow characteristic by the EHT between Randall-Sundrum and Einstein-Gauss-Bonnet black holes have also been considered [8]. Perhaps the most compelling result is that for the Modified Gravity black hole [17], which predicts a shadow radius bigger than that of the standard Kerr solution, depending on the (non-universal) size of the Modified Gravity parameter α.…”

Section: Introductionmentioning

confidence: 99%

“…A second test -the imaging of a black hole's "shadow"/photosphere, and by proxy its event horizonis looming near. Pioneered by the Event Horizon Telescope (EHT) and BlackHoleCam consortia [4,5], it will involve targeting the putative supermassive black hole Sagittarius A* (Sgr A*) at the center of the Milky Way [6], as well as active galactic nuclei [7], and it is anticipated that this will provide a crucial test of GR against competing theories by allowing precision measurements of the horizon size [8].…”

Section: Introductionmentioning

confidence: 99%

Black hole shadows in fourth-order conformal Weyl gravity

Mureika

Varieschi

2017

Can. J. Phys.

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We calculate the characteristics of the "black hole shadow" for a rotating, neutral black hole in fourth-order conformal Weyl gravity. It is shown that the morphology is not significantly affected by the underlying framework, except for very large masses. Conformal gravity black hole shadows would also significantly differ from their general relativistic counterparts if the values of the main conformal gravity parameters, γ and κ, were increased by several orders of magnitude. Such increased values for γ and κ are currently ruled out by gravitational phenomenology. Therefore, it is unlikely that these differences in black hole shadows will be detected in future observations, carried out by the Event Horizon Telescope or other such experiments.

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Testing General Relativity with the Shadow Size of SgrA*

Cited by 168 publications

References 58 publications

Astrophysical imaging of Kerr black holes with scalar hair

Astrophysical imaging of Kerr black holes with scalar hair

BlackHoleCam: Fundamental physics of the galactic center

Black hole shadows in fourth-order conformal Weyl gravity

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