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Rights: © Copyright 2009. University of Waikato. All Rights Reserved.
Published 1 April 2009 Referencing Hub media

Professor Denis Sullivan, from Victoria University of Wellington, measures light from pulsating white dwarfs. He then builds computer models to work out the structure inside the stars.


One of the things that’s preoccupied my research time for nearly 20 years now is looking at pulsating white dwarfs. When you think of a star it’s in a sort of equilibrium – gravity trying to pull it in, some mechanism holding it up. Now if you look at it in a little bit more detail, a lot of these processes means the stars pulsate, they might go in and out like a beating heart, and there are more complicated processes where they sort of quiver.

Well it turns out that White Dwarfs as they cool they get to a certain temperature and then the escaping radiation makes it sort of shake and quiver. Now the surface, you know, changes its form - that means there is light coming off changes that form. So if you observe the light from a White Dwarf, you can see over a period of time, in fact, you know, a couple of minutes you can see its light intensity go up and down, up and down in fact in quite a complicated way. So if you analyse the light, you can get a lot of different frequencies related to how the object quivers.

The White Dwarf oscillates in a complicated way and there’s lots of different frequencies. If you can identify those you can relate that to a model of how the White Dwarf is built and the term for that is Astro-Seismology. We build computer models of the star and then we match the vibrations to what we observe from the light and then we can make these models better and better. The models are actually quite complex, a lot of programming involved, a lot of physics. A lot of my work is observing particular pulsating White Dwarfs, getting the data, reducing it, finding the frequencies and then working with colleagues who know how to crank the handle of the models better than I do.