TY - JOUR

T1 - Black hole shadow as a test of general relativity

T2 - Quadratic gravity

AU - Ayzenberg, Dimitry

AU - Yunes, Nicolás

N1 - Funding Information:
This work was supported by the NSF CAREER Grant PHY-1250636. DA also acknowledges support from the National Natural Science Foundation of China (NSFC), Grant No. U1531117, and Fudan University, Grant No. IDH1512060. NY also acknowledges support from NASA grants NNX16AB98G and 80NSSC17M0041. We would also like to acknowledge the support of the Research Group at Montana State University through their High Performance Computer Cluster Hyalite.
Publisher Copyright:
© 2018 IOP Publishing Ltd Printed in the UK.

PY - 2018/11/5

Y1 - 2018/11/5

N2 - Observations of the black hole shadow of supermassive black holes, such as Sagittarius A∗at the center of our Milky Way galaxy, allow us to study the properties of black holes and the nature of strong-feld gravity. According to the Kerr hypothesis, isolated, stationary, and axisymmetric astrophysical black holes are described by the Kerr metric. The Kerr hypothesis holds in general relativity and in some modifed gravity theories, but there are others in which it is violated. In principle, black hole shadow observations can be used to determine if the Kerr metric is the correct description for black holes, and in turn, they could be used to place constraints on modifed gravity theories that do not admit the Kerr solution. We here investigate whether black hole shadow observations can constrain deviations from general relativity, focusing on two well-motivated modifed quadratic gravity theories: Einstein-dilaton-Gauss- Bonnet gravity and dynamical Chern-Simons gravity. We show that current constraints on Einstein-dilaton-Gauss-Bonnet gravity are stronger than any that could be placed with black hole shadow observations of supermassive black holes. We also show that the same holds for dynamical Chern-Simons gravity through a systematic bias and a likelihood analysis when considering slowly-rotating supermassive black holes. However, observations of more rapidly-rotating black holes, with dimensionless spins |J|/M2 ∼0.5, could be used to better constrain dynamical Chern-Simons gravity.

AB - Observations of the black hole shadow of supermassive black holes, such as Sagittarius A∗at the center of our Milky Way galaxy, allow us to study the properties of black holes and the nature of strong-feld gravity. According to the Kerr hypothesis, isolated, stationary, and axisymmetric astrophysical black holes are described by the Kerr metric. The Kerr hypothesis holds in general relativity and in some modifed gravity theories, but there are others in which it is violated. In principle, black hole shadow observations can be used to determine if the Kerr metric is the correct description for black holes, and in turn, they could be used to place constraints on modifed gravity theories that do not admit the Kerr solution. We here investigate whether black hole shadow observations can constrain deviations from general relativity, focusing on two well-motivated modifed quadratic gravity theories: Einstein-dilaton-Gauss- Bonnet gravity and dynamical Chern-Simons gravity. We show that current constraints on Einstein-dilaton-Gauss-Bonnet gravity are stronger than any that could be placed with black hole shadow observations of supermassive black holes. We also show that the same holds for dynamical Chern-Simons gravity through a systematic bias and a likelihood analysis when considering slowly-rotating supermassive black holes. However, observations of more rapidly-rotating black holes, with dimensionless spins |J|/M2 ∼0.5, could be used to better constrain dynamical Chern-Simons gravity.

KW - black hole shadow

KW - Black holes

KW - general relativity

KW - modifed theories of gravity

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U2 - 10.1088/1361-6382/aae87b

DO - 10.1088/1361-6382/aae87b

M3 - Article

AN - SCOPUS:85056871961

SN - 0264-9381

VL - 35

JO - Classical and Quantum Gravity

JF - Classical and Quantum Gravity

IS - 23

M1 - 235002

ER -