Emergent gravity from nonlinear perturbation of spherical accretion with variable adiabatic index

TL;DR

This work demonstrates that gravity-like effects in accretion flows can emerge from nonlinear perturbations, extending the analogue gravity concept beyond linear approximations in astrophysical fluid dynamics.

Contribution

It extends the acoustic metric formalism to nonlinear regimes in spherical accretion with variable adiabatic index, showing dynamical analogue geometries.

Findings

Nonlinear perturbations satisfy a covariant wave equation in an effective acoustic spacetime.

The acoustic horizon can shift inward or outward depending on fluctuations.

Nonlinear effects make the analogue geometry dynamical and more realistic.

Abstract

The main aim of the present work is to demonstrate that the analogue gravity phenomena are not an artifact of linear perturbation, rather gravity-like effects emerge through the non linear higher order perturbation of transonic fluid as well. To establish that fact, a spherically accreting astrophysical system has been considered where the hydrodynamic accretion with a relativistic, multi-component equation of state with position dependent adiabatic index onto compact astrophysical objects has been considered. By extending the acoustic metric formalism beyond the linear regime, it has been shown that the aforementioned perturbations satisfy a covariant wave equation in an effective acoustic spacetime with non-linear corrections, making the analogue geometry dynamical. As a consequence, the acoustic horizon can shift (inward or outward), depending on the relative amplitudes of density, temperature, and mass accretion-rate fluctuations. This provides a more realistic framework to investigate the dynamics of the non-linear analogue spacetime in astrophysically relevant accretion flows.