New Kind of Star Discovered in Big Dipper

May 2, 2008 -- Astronomers have spotted a new type of stripped-down white dwarf star with a pulsating carbon surface. The new and so far unique white dwarf was predicted to exist somewhere in the cosmos, but was found only because of some massive surveys of the sky.

"They're extremely rare," said astronomer Kurtis Williams of the University of Texas at Austin's McDonald Observatory, where the discovery was made. "It's a real needle in a haystack to find one."

The white dwarf star they discovered is 800 light-years away in the constellation Ursa Major -- a.k.a. the Big Dipper. Its light wavers by almost 2 percent every eight minutes.

Like other white dwarfs, this new star is the remnant of a star which, in its youth, was probably a bright shining star no more than nine times the mass of the sun. In other words, it was neither exceptionally large nor small as stars go.

Today what remains is a glowing sphere smaller than Earth but with a mass equal to our sun and a brightness that's only one six-hundredth of old Sol.

Unlike other white dwarfs, however, this one has been stripped of its outer layers of hydrogen and helium and is left with carbon on its surface. That carbon appears to be at a very toasty 35,100 degrees F (19,500 C), which allows its carbon to shift en masse between a higher and a lower energy state, driven by just one electron per atom. That shifting carbon is visible as the star's pulsation.