Effects of a cosmological constant on the X-ray fluorescence spectra of black hole accretion disks

TL;DR

This study explores how a cosmological constant influences the X-ray spectral features of black hole accretion disks, revealing that it causes the characteristic iron line peaks to diminish and converge, affecting observational signatures.

Contribution

It provides the first analysis of the impact of a cosmological constant on black hole accretion disk spectra, linking spacetime geometry to observable spectral features.

Findings

Peaks in iron line profiles become less pronounced with increasing cosmological constant.

The peaks move closer together as the cosmological constant increases.

Effects are similar to changing the disk's outer radius or emissivity profile.

Abstract

We investigate the effects of cosmological constant on the characteristic peaks in the iron line profile in the black hole accretion disk X-ray spectrum. Our results show that for a fixed mass black hole, the peaks become less pronounced and closer together with increasing cosmological constant. This effect is mainly due to the slower rotational velocity of Keplerian orbits at large radii in the Schwarzschild-de Sitter spacetime as compared to those for the Schwarzschild spacetime. This change of the iron line profile is similar to that obtained from increasing the outer radius of the accretion disk size or reducing the emission intensity power law exponent in the accretion disk emissivity models.