NASA | MSFC | SAO | Chandra X-ray Observatory | 2018 Sep 27
Galaxy clusters are the largest structures in the Universe held together by gravity. While galaxy clusters can contain hundreds or even thousands of individual galaxies, the lion's share of mass in a galaxy cluster comes from hot gas, which gives off X-rays, and unseen dark matter. How did these cosmic giants get to be so big?
This new image shows one way: the capture of galaxies as they are drawn in by the extraordinarily powerful gravity of a galaxy cluster. In the left panel, a wide-field view of the cluster, called Abell 2142, is seen. Abell 2142 contains hundreds of galaxies embedded in multi-million-degree gas detected by Chandra (purple). The center of the galaxy cluster is located in the middle of the purple emission, in the lower part of the image. Only the densest hot gas is shown here, implying that less dense gas farther away from the middle of the cluster is not depicted in the purple emission. In this composite image, the Chandra data have been combined with optical data from the Sloan Digital Sky Survey in red, green, and blue.
A bright X-ray tail located in the upper left of the image is aiming straight for Abell 2142. The right panel contains a closer view of this tail. A galaxy group containing four bright galaxies is near the "head" while the "tail" extends off to the upper left. (Galaxy groups, as defined by astronomers contain a handful to a few dozen galaxies, as opposed to much more populous galaxy clusters.) The direction of the tail and the sharp leading edge of the hot gas around the galaxy group, identified in the labeled version, shows that the group is falling almost directly towards the center of Abell 2142. A close-up view of the four bright galaxies (named G1, G3, G4 and G5) is shown as an optical and X-ray image. The galaxy G2 is a background object, rather than a member of the galaxy group. ...
Deep Chandra Observations of the Stripped Galaxy Group Falling into Abell 2142 ~ Dominique Eckert et al