Messier 87 - Cluster Membership

Cluster Membership

This supergiant elliptical galaxy is located near the center of the Virgo Cluster. This rich cluster has about 2,000 members and it forms the core of the larger Virgo Supercluster, of which the Local Group, and hence the Milky Way galaxy, is an outlying member. The cluster is organized into at least three distinct subsystems that are associated with the three galaxies Messier 87, Messier 49 and Messier 86. In terms of mass, Messier 87 is a dominant member of the cluster, and hence appears to be moving very little relative to the cluster as a whole. Indeed, Messier 87 is defined as the cluster center. The cluster has a sparse gaseous atmosphere that emits X-rays that decrease in temperature toward the middle, where Messier 87 is located. The combined mass of the cluster is estimated to be (0.15–1.5) × 1015 solar masses.

Measurements of the motion of intracluster planetary nebulae between Messier 87 and Messier 86 suggest that these two galaxies are moving toward each other and this may be their first encounter. Messier 87 may have encountered Messier 84 in the past, as evidenced by the truncation of the outer halo of the former from tidal effects. However, another possible cause of this truncation is a contraction due to an unseen mass falling into Messier 87 from the rest of the cluster, which, in particular, may be the hypothesized dark matter. A third possibility is that the halo formation was truncated as a result of early feedback from the active galactic nucleus at the core of Messier 87.