Shadows of CPR black holes and tests of the Kerr metric

Ghasemi-Nodehi, M.; Li, Zilong; Bambi, Cosimo

doi:10.1140/epjc/s10052-015-3539-x

Cited by 65 publications

(50 citation statements)

References 111 publications

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“…These figures show both the shape of the black hole shadow (on the left in each panel) and the function R(φ), which was introduced in Ref. [38] to characterize the shape of the shadow (see Ref. [39] for a more sophisticated description).…”

Section: Black Hole Shadowmentioning

confidence: 99%

Note on a new parametrization for testing the Kerr metric

Ghasemi-Nodehi

Bambi

2016

Eur. Phys. J. C

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We propose a new parametrization for testing the Kerr nature of astrophysical black hole candidates. The common approaches focus on the attempt to constrain possible deviations from the Kerr solution described by new terms in the metric. Here we adopt a different perspective. The mass and the spin of a black hole make the spacetime curved and we want to check whether they do it with the strength predicted by general relativity. As an example, we apply our parametrization to the black hole shadow, an observation that may be possible in a not too distant future.

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Section: Black Hole Shadowmentioning

confidence: 99%

Note on a new parametrization for testing the Kerr metric

Ghasemi-Nodehi

Bambi

2016

Eur. Phys. J. C

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“…This has been the subject of a recent study by Ref. 73, who showed that the near-field image by itself might not be able to detect a deviation from Kerr (as an illustration, see their Figure 5a). However, once the spin measurement from the pulsar done in the Kerr-like far field is combined with the constraints from modeling the shadow, one can recover the deformation (in their case, parameter t 3 ), and test for a violation of the Kerr hypothesis.…”

Section: Combining the Constraints From Different Techniquesmentioning

confidence: 97%

“…Ref. 73). The combination of different methods can in fact break this degeneracy and therefore lead to independent estimates of the BH parameters and to a clean test of the Kerr metric.…”

Section: Combining the Constraints From Different Techniquesmentioning

confidence: 99%

BlackHoleCam: Fundamental physics of the galactic center

Goddi

Falcke

Krämer

et al. 2017

Int. J. Mod. Phys. D

177

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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“…This has been the subject of a recent study by Ref. 175, who showed that the near-field image by itself might not be able to detect a deviation from Kerr (as an illustration, see their Fig. 5(a)).…”

Section: Combining the Constraints From Different Techniquesmentioning

confidence: 97%

“…Ref. 175). The combination of different methods can in fact break this degeneracy and therefore lead to independent estimates of the BH parameters and to a clean test of the Kerr metric.…”

Section: Combining the Constraints From Different Techniquesmentioning

confidence: 99%