Dark Energy Effective Mass (Mᴅᴇ):

In the research paper "Dark energy and the structure of the Coma cluster of galaxies" by Chernin et al. (2013), the concept of Dark Energy Effective Mass ($M_{de}$) is introduced as part of the analysis of the Coma cluster's structure. The paper explores how dark energy, characterized by its antigravitational effects, influences the structure of galaxy clusters.

Description of Dark Energy Effective Mass:

1. Definition and Role:

   • Dark Energy Effective Mass ($M_{de}$) is defined as the effective mass of dark energy that contributes to the gravitational dynamics of a galaxy cluster. Unlike traditional matter, dark energy has a negative effective mass ($M_{de}<0$) due to its repulsive, antigravitational properties. This negative mass affects the total gravitating mass of the cluster.​

2. Mathematical Formulation:

   • The effective mass of dark energy within a spherical volume of radius $R$ is given by: $$M_{de}(R) = \frac{8 \pi}{3} \rho_{de} R^3$$where $\rho_{de}$ is the density of dark energy. For instance, at different radii:
     • At $R = 1.4$ Mpc: $M_{de} = -2.3 \times 10^{12} M_{\odot}$
     • At $R = 4.8$ Mpc: $M_{de}=-9.4\times 10^{13}{M}_{\odot }$
     • At $R = 14$ Mpc: $M_{de} = -2.3 \times 10^{15} M_{\odot}$​

3. Equation for Total Gravitating Mass:

   • The total gravitating mass ($M_g$) within a radius $R$ of a galaxy cluster is the sum of the matter mass ($M_m$) and the dark energy effective mass ($M_{de}$): $$M_g = M_m + M_{de}$$This equation allows us to calculate the total gravitating mass of the cluster by adding the matter mass to the dark energy effective mass. For example, at $R = 14$  Mpc, the total gravitating mass $M_g$ approximates $4.7 \times 10^{15} M_{\odot}$.

4. Implications:

   • The negative effective mass of dark energy implies that, at large distances from the cluster center, the dark energy's repulsive force can exceed the gravitational attraction of the matter within the cluster. This antigravitational effect becomes significant at distances beyond the zero-gravity radius ($R_{zg}$), beyond which the dark energy's influence dominates.

The study by Chernin et al. highlights the substantial impact of dark energy on the structure and mass estimation of galaxy clusters, underscoring its role in shaping cosmic structures and influencing their dynamics.