Cosmological coupling of local gravitational systems

TL;DR

This paper derives a formula for how local gravitational systems, like galaxies, can be influenced by the universe's expansion, especially considering pressure anisotropies, and explores this coupling using galaxy models.

Contribution

It provides a general formula for the cosmological coupling of the Misner-Sharp mass and analyzes its implications for galaxy models.

Findings

Cosmological coupling depends on pressure anisotropies in the weak-field limit.

Galactic mass can be coupled to cosmological dynamics.

Coupling strength varies with the universe's scale factor.

Abstract

We investigate the cosmological coupling of spherical, local astrophysical systems. We derive a general formula quantifying the cosmological coupling of the Misner-Sharp mass of these objects. We show that, in the weak-field limit, the cosmological coupling is only allowed if there are pressure anisotropies. We also apply our results to galaxies, modelling them with the Navarro-Frenk-White and Einasto profiles. We show that the galactic mass can be coupled to the cosmological dynamics and examine its dependence on the scale factor of the universe.