📝 SummarXiv

Abstract

The hydrodynamics of low-angular-momentum, multi-transonic, axisymmetric, inviscid accretion flow onto a rotating black hole has been systematically investigated using three distinct disc geometries and two thermodynamic equations of state, within the framework of a pseudo-Kerr potential. To enhance astrophysical realism, the study incorporates a multi-component galactic potential, modeling the influence of the surrounding stellar distribution, dark matter, and hot gas with the central blackhole. Our analysis reveals that the inclusion of the galactic potential induces subtle yet noteworthy shifts in the locations of sonic points. This effect is particularly pronounced in the vertical equilibrium disc model, where the region allowing for shock formation undergoes significant modification. The nature of critical points is determined by analyzing the eigenvalues of the corresponding stability matrix, establishing that multi-transonicity is restricted to a finite range of angular momentum. Shock strength and associated dynamic \& thermodynamic quantities-such as mach number, pressure, density and temperature-are found to vary sensitively with galactic parameters, and are illustrated through comprehensive parametric plots. Additionally, a time-dependent linear perturbation analysis, demonstrates that the governing perturbation equations retain their structural form even in the presence of a galactic potential. The flows remain stable under adiabatic, radially propagating perturbations. Interestingly, the perturbative framework naturally gives rise to an emergent acoustic metric, identifying the system as a classical analogue of gravity. The corresponding acoustic surface gravity is analytically derived and shown to exhibit a dependence on both the spin of the black hole and the characteristics of the surrounding galactic environment.