# Testing Einstein-dilaton-Gauss-Bonnet gravity from the reflection spectrum of accreting black holes

## TL;DR

This paper investigates whether X-ray reflection spectroscopy can differentiate black holes in Einstein-dilaton-Gauss-Bonnet gravity from those in Einstein's gravity, finding it feasible only with future X-ray observatories.

## Contribution

It demonstrates the potential of future X-ray missions to test alternative gravity theories through black hole reflection spectra.

## Key findings

- Current X-ray missions cannot distinguish the two black hole types.
- Next-generation X-ray facilities may enable this distinction.
- Simulations show observable differences in reflection spectra with future instruments.

## Abstract

Einstein-dilaton-Gauss-Bonnet gravity is a theoretically well-motivated alternative theory of gravity emerging as a low-energy 4-dimensional model from heterotic string theory. Its rotating black hole solutions are known numerically and can have macroscopic deviations from the Kerr black holes of Einstein's gravity. Einstein-dilaton-Gauss-Bonnet gravity can thus be tested with observations of astrophysical black holes. In the present paper, we simulate observations of the reflection spectrum of thin accretion disks with present and future X-ray facilities to understand whether X-ray reflection spectroscopy can distinguish the black holes in Einstein-dilaton-Gauss-Bonnet gravity from those in Einstein's gravity. We find that this is definitively out of reach for present X-ray missions, but it may be achieved with the next generation of facilities.