A new image from the NASA/ESA Hubble Space Telescope shows PSZ2 G138.61-10.84, a colossal galaxy cluster located approximately 6 billion light-years away in the constellation of Andromeda.
Clusters of galaxies are the largest stable systems in the Universe.
They are like laboratories for studying the relationship between the distributions of dark and visible matter.
In 1937, Swiss astronomer Fritz Zwicky realized that the visible component of a galaxy cluster — the thousands of millions of stars in each of the thousands of galaxies — represents only a tiny fraction of the total mass.
About 80-85% of the matter is invisible, the so-called ‘dark matter.’
Galaxy clusters are gravitationally dominated by dark matter but also contain vast quantities of hot gas.
This gas cools by emitting X-ray radiation, decreasing its temperature and allowing more gas to flow to the center.
The galaxy at the center of a cluster sits at the center of the dark matter halo, where also the gas density is highest.
Furthermore, these so-called ‘brightest cluster galaxies’ assembled via many mergers of mostly cluster galaxies.