PHOTON RINGS AROUND KERR AND KERR-LIKE BLACK HOLES

By T. Johannsen. 2013

175 citations recorded by the source corpus.

Very long baseline interferometric observations have resolved structure on scales of only a few Schwarzschild radii around the supermassive black holes at the centers of our Galaxy and M87. In the near future, such observations are expected to image the shadows of these black holes together with a bright and narrow ring surrounding their shadows. For a Kerr black hole, the shape of this photon ring is nearly circular unless the black hole spins very rapidly. Whether or not, however, astrophysical black holes are truly described by the Kerr metric as encapsulated in the no-hair theorem still remains an untested assumption. For black holes that differ from Kerr black holes, photon rings have been shown numerically to be asymmetric for small to intermediate spins. In this paper, I calculate semi-analytic expressions of the shapes of photon rings around black holes described by a new Kerr-like metric which is valid for all spins. I show that photon rings in this spacetime are affected by two types of deviations from the Kerr metric which can cause the ring shape to be highly asymmetric. I argue that the ring asymmetry is a direct measure of a potential violation of the no-hair theorem and that both types of deviations can be detected independently if the mass and distance of the black hole are known. In addition, I obtain approximate expressions of the diameters, displacements, and asymmetries of photon rings around Kerr and Kerr-like black holes.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/88434eb2fadd9d5292b10e03b2393140899f04bf

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. Rahul Kumar
2. Sushant G. Ghosh
3. Cosimo Bambi
4. V. Cardoso
5. Paolo Pani
6. T. Johannsen
7. R. Brito
8. O. Tsupko

In Atomic and Molecular Physics, and Optics

1. Rahul Kumar
2. Sushant G. Ghosh
3. O. Tsupko
4. Paolo Pani
5. R. Brito
6. Dimitrios Psaltis
7. Misba Afrin
8. V. Perlick

Citations in the corpus

• Shadow casted by a Konoplya-Zhidenko rotating non-Kerr black hole (2017, background): “Generally, it is convenient to choice a decomposition connected to a reference frame with zero axial angular momentum in relation to spatial infinity, which is given by [2, 20, 27, 41, 42]”
• TESTING THE NO-HAIR THEOREM WITH EVENT HORIZON TELESCOPE OBSERVATIONS OF SAGITTARIUS A* (2013, methodology): “However, special care must be taken to avoid the region very close to the central object where the quasi-Kerr metric becomes unphysical (Johannsen 2013).”
• Superradiance: Energy Extraction, Black-Hole Bombs and Implications for Astrophysics and Particle Physics (2015, result): “Altogether, these results give further theoretical support to the BH hypothesis: the mere observation of a light ring – a much simpler task than the observation of the event horizon, and something that is within the reach of upcoming facilities [546, 438, 439] – would be conclusive evidence for the ”
• Rotating black holes in 4D Einstein-Gauss-Bonnet gravity and its shadow (2020, background): “of R(φ) from the shadow average radius [106, 107]”
• Shadows and strong gravitational lensing: a brief review (2018, background): “The shadow outline in the sky depends on the gravitational lensing of nearby radiation, thus bearing the fingerprint of the geometry around the BH [21].”
• Calculating black hole shadows: Review of analytical studies (2021, result): “Johannsen [46] x and y (26) and (27) ξ and η (A3) and (A4)”
• A coordinate-independent characterization of a black hole shadow (2015, background): “(iii) They are restricted to a very specific measure of the distortion and are unable to model arbitrary distortion; exceptions are the works of Johannsen & Psaltis (2010) and Johannsen (2013), where instead polar-averaged distortions have been proposed.”
• Parameter estimation of hairy Kerr black holes from its shadow and constraints from M87* (2021, methodology): “…the observables 'B and XB used in the above two methods demand some symmetries in the shadow shape, and they may not work precisely for the haphazard black hole shadows in MoG (Schee & Stuchlik 2009; Johannsen 2013; Tsukamoto et al. 2014; Abdujabbarov et al. 2015; Younsi et al. 2016; Tsupko 2017).”
• Black Hole Parameter Estimation from Its Shadow (2018, background): “…work for black holes in some modified theories of gravity (Abdujabbarov et al. 2015b), which leads to the introduction of new observables (Schee & Stuchlik 2009; Johannsen 2013b; Tsukamoto et al. 2014; Abdujabbarov et al. 2015b; Cunha et al. 2015; Younsi et al. 2016; Tsupko 2017; Wang et al. 2018).”
• Imaging a boson star at the Galactic center (2015, background): “For a Kerr black hole, the shadow slightly changes with the observer’s inclination angle and with the black hole spin parameter (Johannsen 2013).”