Clusters of galaxies are the most massive bound structures in the Universe. They are dark matter dominated (84%), and harbour several hundreds of galaxies that bathe in a hot diffuse intra-cluster medium (ICM). Temperatures of the ICM range between tens of million degrees to hundreds of million degrees. Galaxy clusters are also the most luminous extended X-ray sources in the sky.

A key question in large scale structure formation is how the delicate heating and cooling balance, commonly termed feedback, in these vast objects evolves and is maintained. The current paradigm is that cooling is regulated by the active galactic nucleaus (AGN) within the central cluster galaxies.

A striking feature observed in low redshift galaxy clusters, is the large X-ray cavities being blown into the ICM by the central active galactic nucleus. These cavities, also known as bubbles, are filled with radio emitting particles. The energy stored within them is substantial, and is sufficient to prevent the gas from cooling.

The X-ray group at the University of Cambridge is actively involved in studying the processes that govern feedback, through multi-wavelength observations. The group is also currently involved in researching other cluster related phenomena, including the study of major cluster mergers (the most energetic events since the big bang), probing the limits of the outskirts of galaxy clusters and measuring the gas transport properties in the ICM.