Testing General Relativity with NuSTAR data of Galactic Black Holes

TL;DR

This paper uses NuSTAR X-ray spectra of Galactic black holes to test Einstein's Kerr black hole hypothesis, providing the most precise electromagnetic constraints to date, surpassing previous methods including gravitational wave observations.

Contribution

It introduces advanced relativistic reflection modeling to analyze NuSTAR data, yielding the most stringent electromagnetic constraints on the Kerr black hole hypothesis so far.

Findings

Constraints on the Kerr metric are more stringent than previous electromagnetic methods.

Some sources provide constraints stronger than current gravitational wave results.

The analysis improves the robustness and precision of testing general relativity around black holes.

Abstract

Einstein's theory of General Relativity predicts that the spacetime metric around astrophysical black holes is described by the Kerr solution. In this work, we employ state-of-the-art in relativistic reflection modeling to analyze a selected set of NuSTAR spectra of Galactic black holes to obtain the most robust and precise constraints on the Kerr black hole hypothesis possible today. Our constraints are much more stringent than those from other electromagnetic techniques, and with some sources we get stronger constraints than those currently available from gravitational waves.