Binary X-ray sources in massive Brans-Dicke gravity

TL;DR

This paper investigates how massive Brans-Dicke gravity affects the X-ray emission and accretion disk properties of low-mass black hole binaries, comparing results to standard Schwarzschild solutions.

Contribution

It introduces a model for accretion disks in massive Brans-Dicke gravity and analyzes the impact of scalar field mass on binary system properties.

Findings

Scalar field mass alters accretion disk characteristics.

X-ray spectral features are influenced by modifications in gravity.

Differences from Schwarzschild solutions are quantified.

Abstract

This study focuses on the X-ray emission of low-mass black hole binaries in massive Brans-Dicke gravity. First, we compute the accretion disk adopting the well-known Shakura-Sunyaev model for an optically thick, cool, and geometrically thin disk. Moreover, we assume that the gravitational field generated by the stellar-mass black hole is an analogue of the Schwarzschild space-time of Einstein's theory in massive Brans-Dicke gravity. We compute the most relevant quantities of interest, i.e., i) the radial velocity, ii) the energy and surface density, and iii) the pressure as a function entirely of the radial coordinate. We also compute the soft spectral component of the X-ray emission produced by the disk. Furthermore, we investigate in detail how the mass of the scalar field modifies the properties of the binary as described by the more standard Schwarzschild solution.