Properties of accretion flow in deformed Kerr spacetime

TL;DR

This study investigates the properties of low-angular momentum accretion flows in deformed Kerr spacetimes, revealing shock transitions, parameter space modifications, and the possibility of accretion with zero angular momentum, with implications for black hole and naked singularity physics.

Contribution

It is the first to analyze shock transitions in accretion flows with zero angular momentum in significantly deformed Kerr spacetimes, including the transition from black holes to naked singularities.

Findings

Global transonic solutions exist in non-Kerr spacetime.

Shock solutions are possible over a wide parameter range.

Deformation parameter reduces and shifts the shock parameter space.

Abstract

We study the properties of a low-angular momentum, inviscid, advective accretion flow in a deformed Kerr spacetime under the framework of general theory of relativity. We solve the governing equations that describe the flow motion in terms of input parameters, namely energy ($E$), angular momentum ($\lambda$), spin ($a_{\rm k}$) and deformation parameter ($\varepsilon$), respectively. We find that global transonic accretion solutions continue to exist in non-Kerr spacetime. Depending on the input parameters, accretion flow is seen to experience shock transition and we find that shocked induced accretion solutions are available for a wide range of the parameter space in $\lambda-E$ plane. We examine the modification of the shock parameter space with $\varepsilon$, and find that as $\varepsilon$ is increased, the effective region of the parameter space is reduced, and gradually shifted towards the higher $\lambda$ and lower $E$ domain. In addition, for the first time in the literature, we notice that accretion flow having zero angular momentum admits shock transition when spacetime deformation is significantly large. Interestingly, beyond a critical limit of $\varepsilon^{\rm max}$, the nature of the central object alters from black hole (BH) to naked singularity (NS) and we identify $\varepsilon^{\rm max}$ as function of $a_{\rm k}$. Further, we examine the accretion solutions and its properties around the naked singularity as well. Finally, we indicate the implications of the present formalism in the context of astrophysical applications.