Dark energy and the structure of the Coma cluster of galaxies

TL;DR

This paper investigates how dark energy influences the structure and mass estimates of the Coma galaxy cluster, proposing a new density profile and considering the zero-gravity radius to refine understanding of its size and mass.

Contribution

It introduces a new matter density profile for the Coma cluster that incorporates dark energy effects and estimates the cluster's maximum size and mass considering the zero-gravity radius.

Findings

Dark energy significantly affects the cluster at radii larger than 14 Mpc.

The proposed density profile fits observational data well from 1.4 to 14 Mpc.

The maximum size of the Coma cluster is about 20 Mpc with a matter mass up to 6.2×10^15 solar masses.

Abstract

{We consider the Coma cluster of galaxies as a gravitationally bound physical system embedded in the perfectly uniform static dark energy background as implied by the $\Lambda$CDM cosmology.} {We ask if the density of dark energy is high enough to affect the structure of a large rich cluster of galaxies?} {We use recent observational data on the cluster together with our theory of local dynamical effects of dark energy, including the zero-gravity radius $R_{\rm ZG}$ of the local force field as the key parameter.} {1) Three masses are defined which characterize the structure of a regular cluster: the matter mass $M_{\rm M}$, the dark-energy effective mass $M_{\rm DE}$ ($<0$) and the gravitating mass $M_{\rm G}$ ($= M_{\rm M} + M_{\rm DE}$). 2) A new matter density profile is suggested which reproduces well the observational data for the Coma cluster in the radius range from 1.4 Mpc to 14 Mpc and takes into account the dark energy background. 3) Using this profile, we calculate upper limits for the total size of the Coma cluster, $R \le R_{\rm ZG} \approx 20$ Mpc, and its total matter mass, $M_{\rm M} \la M_{\rm M}(R_{\rm ZG}) = 6.2 \times 10^{15} M_{\odot}$.} {The dark energy antigravity affects strongly the structure of the Coma cluster at large radii $R \ga 14$ Mpc and should be taken into account when its total mass is derived.}