e Astrophysics & Space Research Group :: Research & Facilities :: Extragalactic Astrophysics

Research: Galaxy Clusters & Large Scale Structure

Clusters of galaxies are the largest gravitationally bound structures in dynamical equilibrium in the universe and as such are extremely interesting both in cosmological terms and in their own right. They consist mainly of dark matter and hot intracluster gas with a temperature of 10-100 million Kelvin, the galaxies themselves constituting a small percentage of the total mass of the cluster. The Birmingham group has programmes underway to study the hot gas and the galaxies in clusters using a combination of X-ray and optical observations coupled with modelling and dynamical calculations.

One important feature of galaxy clusters is that radiation from background sources, such as quasars or distant galaxies, is bent as it passes near the deep gravitational potential well of the cluster. This phenomenon, known as gravitational lensing, can be used to explore the cluster potential, the lensed sources and the geometry of the Universe.

On even larger scales, clusters are grouped into superclusters. These huge filamentary structures extend over tens of millions of light years, and the gravitational pull of their very large masses cause large scale patterns in the velocities of galaxies. For example, the Milky Way is being pulled towards a region called the "Great Attractor".

Further details of our work in these areas can be found below:

coma_xray

coma_opt

The Coma cluster is one of the nearest rich clusters of galaxies. It had generally been thought of as a rather structureless and well evolved cluster. The X-ray image above left, obtained with the XMM-Newton telescope, shows clear signs of complex substructures in the hot intracluster gas. This probably indicates that the cluster has a lively recent history, and has swallowed a number of smaller clusters within the past few billion years. For comparison, the scale bar in the top left corner is 1/3 of the angular size of the full moon. The optical image of the cluster centre on the right, shows the two yellowish giant elliptical galaxies which dominate the core region. Almost all the sources seen in this image, apart from the bright blue foreground star, are galaxies within the cluster.