May 22, 1995: Peering into the heart of two recently exploded
double-star systems, the Hubble telescope has surprised
researchers by finding that the white dwarf stars at the center
of the fireworks are cooler than expected and spin more slowly
than previously thought. Each dwarf - dense, burned-out stars
that have collapsed to the size of Earth - is in a compact
binary system, called a cataclysmic variable, where its
companion is a normal star similar to, but smaller than the Sun.
The stars are so close together that the entire binary system
would fit inside the Sun. Their closeness allows gas to flow
from the normal star onto the dwarf, where it swirls into a
pancake-shaped disk [see illustration]. When the disk of gas
periodically collapses onto the white dwarf, it unleashes a
burst of kinetic energy, called a dwarf nova outburst. Once
dumped onto the dwarf's surface, hydrogen accumulates until it
undergoes thermonuclear fusion, which eventually triggers an
explosion.See the rest: