Quasinormal modes, Hawking radiation and absorption of the massless scalar field for Reissner–Nordström black hole surrounded by a cloud of strings in Rastall gravity

Abstract

In this work, we investigate the quasinormal modes (QNMs), shadow radius, gray-body factor, Hawking radiation and absorption cross-section of the Reissner–Nordström black hole surrounded by a cloud of strings in Rastall gravity for a massless scalar field. We use the sixth-order Wenzel, Kramers and Brillouin (WKB) and unstable circular null geodesic methods to calculate QNMs. Moreover, the values obtained by the two methods are in very good agreement. The real part and absolute value of imaginary part of quasinormal frequencies decrease with the increase of [Formula: see text]. As [Formula: see text] increases, the real part of quasinormal frequencies increases while the absolute value of imaginary part first increases and then decreases. For [Formula: see text], they decrease with the increase of [Formula: see text]. While they first increase and then decrease with [Formula: see text] increasing at small value of [Formula: see text] when [Formula: see text]. Then using the unstable circular null geodesic method, we obtain the shadow radius of black hole. We find that shadow radius decreases first and then increases as the negative parameter [Formula: see text] increases. We also calculate the gray-body factor. According to it, Hawking radiation and absorption cross-section are calculated. We explore the influence of [Formula: see text], [Formula: see text] and [Formula: see text] on the energy emission rate. When other parameters are fixed, the black hole lives longer as [Formula: see text], positive parameter [Formula: see text] and [Formula: see text] increase. To obtain absorption cross-section, we adopt the partial wave method and sinc approximation method, and the results obtained by two methods have excellent consistency at mid-high frequency region. Further, we assess the effect of [Formula: see text], [Formula: see text] and [Formula: see text] on the absorption cross-section.