A bound system in the expanding universe with modified holographic Ricci dark energy and dark matter

TL;DR

This paper investigates the evolution of bound systems within an expanding universe modeled by modified holographic dark energy, revealing a three-stage process including expansion, a stable phase, and a future big rip, with implications for galaxy dynamics.

Contribution

It introduces a new analysis of bound system evolution in a universe with modified holographic dark energy, including geodesic derivation and critical angular momentum insights.

Findings

Galaxy undergoes expansion, stability, then big rip.

Test particles require less angular momentum to escape over time.

Bound systems are affected by the universe's dark energy dynamics.

Abstract

The evolution of a bound system in the expanding background has been investigated in this paper. The background is described by a FRW universe with the modified holographic dark energy model, whose equation of state parameter changes with time and can cross the phantom boundary. To study the evolution of the bound system, an interpolating metric is considered, and on this basis the geodesics of a test particle are given. The equation of motion and the effective potential are also derived from the geodesics. By studying the the effective potential and the evolution of the radius of a test particle in the bound system of the Milky Way galaxy, we have found that the galaxy would go through three stages: expands from a singular point; stays in a discoid for a period of time; big rip in the future. With the help of analysing the critical angular momentum, we find that the test particle needs less angular momentum to escape from the center mass as time passes.