Galaxy groups and clusters

Galaxy groups and clusters are the largest known gravitationally bound objects to have arisen thus far in the process of cosmic structure formation.

When observed visually, clusters appear to be collections of galaxies held together by mutual gravitational attraction.

X-ray studies have revealed the presence of large amounts of intergalactic gas known as the intracluster medium.

This gas is very hot, between 107K and 108K, and hence emits X-rays in the form of bremsstrahlung and atomic line emission.

Since this gas is in approximate hydrostatic equilibrium with the overall cluster gravitational field, the total mass distribution can be determined.

Brownstein and Moffat[8] use a theory of modified gravity to explain X-ray cluster masses without dark matter.

The density, temperature, and substructure of the intracluster X-Ray gas therefore represents the entire thermal history of cluster formation.

MACS J0152.5-2852 is a massive galaxy cluster. Almost every pixel seen in the image is a galaxy, each containing billions of stars. [ 1 ]
Map of the positions of thousands of galaxies in the VIPERS survey [ 3 ]
Rich scattering of galaxies was captured by the MPG/ESO telescope .
Galaxy cluster ACO 3341 seen by VLT 's VIMOS
Galaxy Cluster LCDCS-0829 acting like a giant magnifying glass. This strange effect is called gravitational lensing .
The Most Distant Mature Galaxy Cluster [ 13 ] taken with ESO's Very Large Telescope in Chile and with NAOJ's Subaru Telescope in Hawaii