TESTING THE NO-HAIR THEOREM WITH EVENT HORIZON TELESCOPE OBSERVATIONS OF SAGITTARIUS A*

By A. Broderick, T. Johannsen, Abraham Loeb, Dimitrios Psaltis. 2013

177 citations recorded by the source corpus.

The advent of the Event Horizon Telescope (EHT), a millimeter-wave very long baseline interferometric array, has enabled spatially resolved studies of the subhorizon-scale structure for a handful of supermassive black holes. Among these, the supermassive black hole at the center of the Milky Way, Sagittarius A* (Sgr A*), presents the largest angular cross section. Thus far, these studies have focused on measurements of the black hole spin and the validation of low-luminosity accretion models. However, a critical input in the analysis of EHT data is the structure of the black hole spacetime, and thus these observations provide the novel opportunity to test the applicability of the Kerr metric to astrophysical black holes. Here we present the first simulated images of a radiatively inefficient accretion flow (RIAF) around Sgr A* employing a quasi-Kerr metric that contains an independent quadrupole moment in addition to the mass and spin that fully characterize a black hole in general relativity. We show that these images can be significantly different from the images of an RIAF around a Kerr black hole with the same spin and demonstrate the feasibility of testing the no-hair theorem by constraining the quadrupolar deviation from the Kerr metric with existing EHT data. Equally important, we find that the disk inclination and spin orientation angles are robust to the inclusion of additional parameters, providing confidence in previous estimations assuming the Kerr metric based on EHT observations. However, at present, the limits on potential modifications of the Kerr metric remain weak.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/73ee0748476a690a4b51eb85b2b401bc5a49320d

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In Astronomy and Astrophysics

1. Paolo Pani
2. V. Cardoso
3. P. Cunha
4. Cosimo Bambi
5. Carlos A. R. Herdeiro
6. S. Vagnozzi
7. D. Mota
8. A. Allahyari

Citations in the corpus

• Magnetically charged black holes from non-linear electrodynamics and the Event Horizon Telescope (2019, background): “At any rate, BH shadows appear to be an extremely promising arena for testing deviations from GR [24–28], and in particular violations of the no-hair theorem [29–31].”
• Shadows and strong gravitational lensing: a brief review (2018, background): “the Kerr geometry) in this crucial region [18].”
• Tests for the existence of black holes through gravitational wave echoes (2017, background): “Imaging these shadows for the supermassive dark source SgrA∗ at the center of our galaxy is the main goal of the Event Horizon Telescope [5, 6].”
• Testing black hole candidates with electromagnetic radiation (2015, methodology): “Employing a radiatively inefficient accretion flow model, Broderick et al. (2014) have explored the capability of present observations to constrain possible deviations from the Kerr geometry.”