Difficulties of quantitative tests of the Kerr-hypothesis with X-ray observations of mass accreting black holes

2018/06/30 by Henric Krawczynski · 34 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Binary black hole #Black hole (networking) #Galaxies: Formation, Evolution, Phenomena #Intermediate-mass black hole #Kerr metric #Stellar black hole #Stellar mass #Supermassive black hole #astro-ph.HE

paper · pdf · doi:10.1007/s10714-018-2419-8

published in General Relativity and Gravitation 50(8) (Springer Science+Business Media) · Review paper from the General Relativity and Gravitation (GRG) Topical Collection "Testing the Kerr spacetime with gravitational-wave and electromagnetic observations" (Guest Editor: Emanuele Berti), accepted version, https://doi.org/10.1007/s10714-018-2419-8

openalex created_date 2018/07/10 · openalex publication_date 2018/07/24 · arxiv created 2018/07/25 · arxiv updated 2018/07/26 · openalex updated_date 2026/08/05

Abstract

X-ray studies of stellar mass black holes in X-ray binaries and mass-accreting supermassive black holes in Active Galactic Nuclei have achieved a high degree of maturity and have delivered detailed information about the astrophysical sources and the physics of black hole accretion. In this article, I review recent progress made towards using the X-ray observations for testing the "Kerr hypothesis" that the background spacetimes of all astrophysical quasi-stationary black holes are described by the Kerr metric. Although the observations have indeed revealed clear evidence for relativistic effects in strong-field gravity, quantitative tests of the Kerr hypothesis still struggle with theoretical and practical difficulties. In this article, I describe several recently introduced test metrics and review the status of constraining the background spacetimes of mass accreting stellar mass and supermassive black holes with these test metrics. The main conclusion of the discussion is that astrophysical uncertainties are large compared to the rather small observational differences between the Kerr and non-Kerr metrics precluding quantitative constraints on deviations from the Kerr metric at this point in time. I conclude with discussing future progress enabled by more detailed numerical simulations and by future X-ray spectroscopy, timing, polarimetry, and interferometry missions.

Citations

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Cited by

• Square Peg in a Circular Hole: Choosing the Right Ansatz for Isolated Black Holes in Generic Gravitational Theories
• Testing the Kerr Black Hole Hypothesis with GX 339–4 by a Combined Analysis of Its Thermal Spectrum and Reflection Features