Study of relativistic accretion flow in Kerr-Taub-NUT spacetime

Abstract

We study the properties of the relativistic, steady, axisymmetric, low angular momentum, inviscid, advective, geometrically thin accretion flow in a Kerr-Taub-NUT (KTN) spacetime which is characterized by the Kerr parameter (ak) and NUT parameter (n). Depending on ak and n values, KTN spacetime represents either a black or a naked singularity. We solve the governing equations that describe the relativistic accretion flow in KTN spacetime and obtain all possible global transonic accretion solutions around KTN black hole in terms of the energy (E) and angular momentum (λ) of the flow. We identify the region of the parameter space in λ-E plane that admits the flow to possess multiple critical points for KTN black hole. We examine the modification of the parameter space due to ak and n and find that the role of ak and n in determining the parameter space is opposite to each other. This clearly indicates that the NUT parameter n effectively mitigate the effect of black hole rotation in deciding the accretion flow structure. Further, we calculate the disc luminosity (L) corresponding to the accretion solutions around the KTN black hole and for a given set of ak and n, we obtain the maximum luminosity (Lmax) by freely varying λ and E. We observe that Lmax decreases with the increase of n irrespective of ak. In addition, we also investigate all possible flow topologies around the naked singularity and find that there exists a region around the naked singularity which remains inaccessible to the flow. We study the critical point properties for naked singularities and find that the flow possesses maximum of four critical points. Finally, we obtain the parameter space for multiple critical points for naked singularity and find that parameter space is shrunk and shifted to lower λ and higher E side as ak is increased which ultimately disappears. © 2020 American Physical Society.