This is an artist's concept of a cataclysmic binary star system. The normal low mass star at upper left is in orbit about a more massive, but much smaller, white dwarf star, which is situated at the center of the disk of material to the lower right. The stars are in such a close orbit, and the gravity of the white dwarf star is so strong, that material escaping from the normal star is captured by the white dwarf. This material, which has angular momentum, swirls in onto the white dwarf, forming a flat, rotating disk. The material in this disk heats up to temperatures of tens of thousands of degrees, emitting strongly at ultraviolet wavelengths. HUT astronomers will try and understand the complex processes that occur in these star systems.
(Image courtesy of Dana Berry and the Astronomical Visualization Laboratory at the Space Telescope Science Institute.)