Astronomers Discover New Type of Pulsating White Dwarf Star
News story originally written on May 1, 2008
Most of the stars in the universe, including the Sun, will end their lives as white dwarf stars. Two astronomers from the University of Texas at Austin, Michael H. Montgomery and Kurtis A. Williams, have discovered a new type of white dwarf star, which is called a "pulsating carbon white dwarf." This is the first new class of white dwarf star discovered in more than 25 years.
A white dwarf star is what is leftover of a Sun-like star that has burned all of the fuel in its core. Until recently, scientists thought there were two main types of white dwarfs: those with an outer layer of hydrogen (about 80 percent of white dwarfs), and those with an outer layer of helium, whose hydrogen shells have somehow been stripped away (the other 20 percent).
Last year, astronomers from the University of Arizona discovered a third type of white dwarf star. These "hot carbon white dwarfs" have had both their hydrogen and helium shells stripped off, leaving their carbon layer exposed. Astronomers think that these could be among the most massive white dwarfs of all, the leftovers of stars that are slightly too small to end their lives in a supernova explosion.
After these new carbon white dwarfs were announced, Dr. Montgomery thought that pulsations in these stars were possible. Astronomers are interested in pulsating stars because the changes in the light put out can show what goes on in their interiors. This is similar to the way geologists study seismic waves from earthquakes to understand what goes on in Earth's interior. In fact, this type of star-study is called "asteroseismology."
So, Dr. Montgomery and Dr. Williams' team began to study carbon white dwarfs with a telescope, looking for pulsators. One of their graduate students, Steve DeGennaro, discovered that a star about 800 light-years away in the constellation Ursa Major fits the bill.
Studying these stars will shed light on the unknown process that strips away their surface layers of hydrogen and helium to lay bare their carbon interiors.