Astrophysics

The X-Ray and Observational Astronomy group has several different specific research interests, which are outlined here with links to the relevant pages.

Gamma Ray Bursts

Gamma-ray bursts (GRBs) are the most powerful explosive events in the Universe (after the Big Bang). They are thought to arise either from the death of a single massive star or from the merger of two compact objects. In both cases a black hole is born which accretes matter for a brief time and launches two, narrow, highly relativistic jets.

Active Galactic Nuclei

At the heart of virtually every large galaxy lurks a supermassive black hole with a mass of a million to more than a billion times that of the Sun. Most of these black holes are dormant, but a few per cent are 'active' meaning that they are drawing inwards material from their host galaxy, this forms an accretion disc that feeds the black hole. As the material spirals through the disc it releases vast amounts of energy as heat and light.

Our Galaxy and Nearby Galaxies

From star birth to death, from the most diffuse interstellar plasmas to the most compact stellar forms, X-rays can provide crucial information pertaining to the structure and evolution of spiral galaxies and their constituent parts.

We are currently engaged in three inter-relating projects in this area.

Surveys

Surveys - essentially mapping the sky - play a pivotal role in all observational  astronomy for example by providing the catalogues of objects and their properties. Surveys in different part of the electromagnetic spectrum give us a multi-wavelength view of the Universe and a means to make an accurate census of different object types.

Cataclysmic Variables

Cataclysmic Variable stars are binary star systems where a white dwarf and a normal star orbit each other so closely that the white dwarf star drags gas away from its Sun-like companion, at a rate of over a thousand million tonnes per second.

White Dwarfs

White dwarf stars play a key role in some of the most important astronomical questions of our day. Their space and luminosity distributions help map out the history of star formation in the Galaxy and can be used to determine the age of the disk. They are also believed to play a significant role in the production of the cosmologically important type Ia supernovae, through stellar mergers or mass transfer. White dwarfs have an intimate relationship with interstellar gas, a fundamental component of the Milky Way and other galaxies.

Brown Dwarfs

Brown dwarfs are best thought of as failed stars, straddling the realms of low-mass stars (typically a tenth of a solar mass) and planets (Jupiter-like objects). Our brown dwarf research deals with the search for nearby and old field brown dwarfs, and young and more distant ones in open clusters, including the Pleiades, Alpha Per, Hyades, Collinder 359, and Coma Ber.

Planets

The search for planets orbiting other stars in our galaxy (exoplanets/extrasolar planets) is a fascinating and rapidly growing field of research. Most of the >200 exoplanets discovered so far have been found by indirect observation methods, eg by radial velocity ("stellar wobble") and transit methods. There are several recent claims for directly imaged very young planets (<10 million years old), but the exact evolutionary status of these objects is controversial. To date, no-one has directly seen an old, mature bona-fide exoplanet like the Jovian gas giants in our solar system.

Supernova Remnants

SNRs are a key, visible link in the cycle that produces the heavy elements; stellar birth, nuclear burning in the stellar core, stellar death - a supernova explosion, supernova remnant, dispersal of material into the interstellar medium, stellar birth...

Solar Wind Charge Exchange

Charge exchange occurs when an electron is transferred from a neutral atom or molecule to an ion, and in the subsequent relaxation of the ion, a photon is emitted. Charge exchange is increasingly being seen as an important emission process throughout the Universe. When the ions concerned originate in the solar wind, this process is known as solar wind charge exchange (SWCX). SWCX occurs throughout the Solar System, for example within planetary exospheres, in the coma of comets or throughout interplanetary space. This emission can be detected by X-ray observatories such as XMM-Newton. SWCX emission is used to inform us about the state of the solar wind, and also, in the future, may be used to image large areas of the Earth's magnetosheath with the aim to increase our understanding of the relationship between the Sun and the Earth.

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