Shadow, absorption and Hawking radiation of a Schwarzschild black hole surrounded by a cloud of strings in Rastall gravity

Abstract

This paper studies the black hole shadow, absorption cross section, and Hawking radiation of a massless scalar field in the background of a static spherically symmetric black hole spacetime that is surrounded by a cloud of strings in Rastall gravity. Specifically, the effects of the parameters a and $\beta$ on the photon sphere and shadow radii are investigated. The results show that as the negative parameter $\beta$ decreases, the photon sphere and shadow radii change in an N-shape. In addition, the absorption cross section obtained after solving the massless Klein–Gordon equation is calculated using the sinc approximation and the partial waves method. We compare the absorption cross section obtained by the sinc approximation and the partial waves method, and find it to be exceptionally consistent in the mid-to-high frequency region. Furthermore, the effects of parameters a and $\beta$ on absorption are examined in detail. Finally, we study in detail the effects of the parameters a, $\beta$ and l on the Hawking radiation power emission spectrum of the considered black hole. It turns out that the string parameter a always suppresses the power emission spectrum, indicating that such black holes live longer when the string parameter a is increased while other parameters are fixed.