Our research revolves around X-ray astronomy and observational cosmology, concentrating on the overlap between these two. The group is led by Prof. Steve Allen (publication list).

Galaxy clusters and cosmology

Galaxy clusters are the largest objects in the Universe, spanning 10 million light years across and containing as much mass as a million, billion suns. Our research examines the physics of these remarkable systems using the best available multi-wavelength data, and uses the observed properties of clusters to probe the nature of dark matter, the weakly interacting yet dominant matter component of the Universe, and dark energy, the driving force behind cosmic acceleration.

Most of the normal, baryonic matter in the Universe is in gaseous form. Within galaxy clusters, the enormous gravity squeezes this gas, heating it to 100 million degrees and causing it to shine brightly at X-ray wavelengths. The X-ray brightness at a given radius reflects the gas density; the temperature, measured by X-ray spectroscopy, reflects the total mass (dark-plus-normal matter). Thus, as well as enabling us to observe clusters out to high redshifts, X-ray observations, made with satellite observatories like Chandra and XMM-Newton allow us to measure the masses of both the baryonic and dark, non-baryonic matter within them.

For an introduction to this work, see e.g.:

Black holes, jets and galaxy formation

Classical models for galaxy formation predict that the largest galaxies should be much brighter than we observe. A large power source must be preventing gas from cooling and forming vast numbers of new stars. We were part of one of the first teams to show that supermassive black holes are likely to be responsible for the suppression of star formation, pumping out huge amounts of energy from the hearts of galaxies in the form of relativistic jets. These jets inflate giant cavities in the X-ray emitting gas and generate enormous sound waves. Recently, we have also shown that this `feedback' occurs with a high and near-universal efficiency, potentially sufficient to solve the galaxy formation problem. However, significant questions relating to the `duty-cycle' of black hole heating, the accretion process, jet formation and black hole growth remain.

For an introduction to this work, see e.g.:

Cluster Surveys

We have been involved in the construction and/or utilization of some of the most powerful X-ray cluster catalogs ever made, including the ROSAT Brightest Cluster Sample, the Extended Brightest Cluster Sample and the Massive Cluster Survey. We are currently carrying out detailed multi-wavelength follow-up of the sources in these catalogs, including deep gravitational lensing studies, optical imaging and spectroscopy, infrared studies and radio observations. For this, we use instruments such as the Hubble Space Telescope, Subaru Telescope, Spitzer Space Observatory and the Very Large Array.

Future missions

We are involved in the development of new X-ray satellite observatories such as The International X-ray Observatory (IXO) and The Wide-Field X-ray Telescope (WFXT), and ground-based optical telescopes such as the Large Synoptic Survey Telescope, which aim to push back the boundaries of our understanding of the Universe:


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