Introduction

Our group in the Department of Physics and Astronomy is currently researching into four different categories of small bodies outside the solar system. These are White Dwarfs, Red Dwarfs, Brown Dwarfs and Extrasolar Planets. A brief explanation of each is given below:

White Dwarfs:

A white dwarf is produced when a low-mass star (up to eight solar masses) reaches the end of its life. After the red giant stage, the star loses its outer layers and they form a planetary nebula. The interior of the star falls in and forms a very hot, dense core – a white dwarf, which emits electromagnetic radiation mainly in ultraviolet and x-ray wavebands. This will gradually cool over time.

If the stellar remnant is greater than 1.4 solar masses, however (the Chandrasekhar limit), the star will be too massive to be supported by electron degeneracy pressure. It will collapse in on itself and eventually explode in a supernova.

A white dwarf is extremely dense as well as extremely hot – a sugar cube-sized piece of white dwarf would weigh as much as two elephants!

Red Dwarfs:

A red dwarf is a very low-mass main sequence star, up to one third of the mass of the Sun. They are very dim and burn very slowly, so are estimated to have very long lifetimes. They are not hot enough to burn helium once their supply of hydrogen has run out, so will simply contract and cool down. They can never become red giants. However, no red dwarfs have yet lived long enough to evolve off the main sequence, as the universe is not old enough. Red dwarfs are emit mainly in the visible and infrared spectra.

Brown Dwarfs:

Brown dwarfs are not stars as they do not undergo hydrogen fusion. They can range from about 5 to 90 times the mass of Jupiter, but are generally only about the same diameter. Brown dwarfs above thirteen times the mass of Jupiter can fuse deuterium (heavy hydrogen).

Extrasolar Planets:

Extrasolar planets are planets outside our solar system. They can be detected with a powerful telescope by observing the light they reflect from their star, or by observing the periodic ‘wobble' they cause in the light of that star. Gravitational interaction between the two bodies produces periodic longitudinal motion in the star relative to the Earth, so the Doppler shift in the light changes and this change can be measured and plotted over time. The magnitude and frequency of this wobble can indicate the mass, orbital speed and orbital radius of such a planet.

Other methods include the transit method - observing the planet's shadow move across the star - and gravitational microlensing - examining the way te gravitational interaction between the star and planet lenses the light of a more distant star.

To find out more about research in these areas, use the buttons above to navigate to the respective home pages.