TESTING THE NO-HAIR THEOREM WITH OBSERVATIONS IN THE ELECTROMAGNETIC SPECTRUM. II. BLACK HOLE IMAGES

By T. Johannsen, Dimitrios Psaltis. 2010

307 citations recorded by the source corpus.

According to the no-hair theorem, all astrophysical black holes are fully described by their masses and spins. This theorem can be tested observationally by measuring (at least) three different multipole moments of the spacetimes of black holes. In this paper, we analyze images of black holes within a framework that allows us to calculate observables in the electromagnetic spectrum as a function of the mass, spin, and, independently, the quadrupole moment of a black hole. We show that a deviation of the quadrupole moment from the expected Kerr value leads to images of black holes that are either prolate or oblate depending on the sign and magnitude of the deviation. In addition, there is a ring-like structure around the black hole shadow with a diameter of ∼10 black hole masses that is substantially brighter than the image of the underlying accretion flow and that is independent of the astrophysical details of accretion flow models. We show that the shape of this ring depends directly on the mass, spin, and quadrupole moment of the black hole and can be used for an independent measurement of all three parameters. In particular, we demonstrate that this ring is highly circular for a Kerr black hole with a spin a ≲ 0.9 M, independent of the observer's inclination, but becomes elliptical and asymmetric if the no-hair theorem is violated. Near-future very long baseline interferometric observations of Sgr A* will image this ring and may allow for an observational test of the no-hair theorem.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/b1547fe7bf5cb51375346bb35b0314f16ade6081

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Citations in the corpus

TESTING THE NO-HAIR THEOREM WITH EVENT HORIZON TELESCOPE OBSERVATIONS OF SAGITTARIUS A* (2013, methodology): “More importantly, the neglected part of the image includes the photon ring, the shape of which directly imprints the structure of the spacetime (Johannsen & Psaltis 2010b).”
Testing black hole candidates with electromagnetic radiation (2015, unknown): “…& Eiroa, 2012, 2013; Amarilla et al., 2010; Atamurotov et al., 2013a,b; Bambi, 2013f; Bambi et al., 2012; Bambi & Freese, 2009; Bambi & Yoshida, 2010; Ghasemi-Nodehi et al., 2015; Johannsen & Psaltis, 2010; Li & Bambi, 2014a; Schee & Stuchĺık, 2009; Tsukamoto et al., 2014; Wei & Liu, 2013).”
TESTING THE NO-HAIR THEOREM WITH OBSERVATIONS IN THE ELECTROMAGNETIC SPECTRUM. IV. RELATIVISTICALLY BROADENED IRON LINES (2012, methodology): “The geometry is the same as in Psaltis & Johannsen (2012) and Johannsen & Psaltis (2010b).”
Imaging a boson star at the Galactic center (2015, background): “Many articles have investigated whether alternative compact objects exhibit differences with respect to Kerr predictions (Bambi & Freese 2009; Johannsen & Psaltis 2010; Amarilla et al. 2010; Amarilla & Eiroa 2013; Vincent 2014; Moffat 2015; Cunha et al. 2015).”
The shape of the black hole photon ring: A precise test of strong-field general relativity (2020, unknown): “[43–46] and references therein).”
A coordinate-independent characterization of a black hole shadow (2015, background): “…of a black hole via radio observations will allow one to test the predictions of general relativity for the radius of the shadow and study astrophysical phenomena in the vicinity of black holes [see Johannsen & Psaltis (2010) and, more recently, Zakharov (2014) for c© 0000 RAS ar X iv :1 50 3.”
Lensing by Kerr black holes (2019, unknown): “However, it is very nearly circular everywhere across this parameter space, except in the extremal, edge-on limit, where it becomes flattened on one side [8, 16, 18, 19, 29].”