Particle scattering by a test fluid on a Schwarzschild spacetime: the equation of state matters

TL;DR

This paper studies how the equation of state of a surrounding perfect fluid affects the motion of test particles near a Schwarzschild black hole, revealing potential observational signatures of cosmic matter properties.

Contribution

It demonstrates that the fluid's equation of state parameter significantly influences particle trajectories, offering a new method to probe cosmic matter characteristics.

Findings

Particles are captured or escape depending on the fluid's equation of state.

Trajectory deviations from geodesic motion depend on the parameter w.

Potential for using particle trajectories to infer properties of cosmic matter.

Abstract

The motion of a massive test particle in a Schwarzschild spacetime surrounded by a perfect fluid with equation of state $p_0= w \rho_0$ is investigated. Deviations from geodesic motion are analyzed as a function of the parameter $w$, ranging from $w=1$ which corresponds to the case of massive free scalar fields, down into the so-called "phantom" energy, with $w<-1$. It is found that the interaction with the fluid distribution leads to capture (escape) of the particle trajectory in the case $1+w>0$ ($<0$), respectively. Based on this result, it is argued that inspection of the trajectories of test particles in the vicinity of a Schwarzschild black hole may offer a new means of gaining insights into the nature of cosmic matter.