This composite image shows Z Camelopardalis, or Z Cam, a double-star
system featuring a collapsed, dead star, called a white dwarf, and a
companion star, as well as a ghostly shell around the system. The massive
shell provides evidence of lingering material ejected during and swept up
by a powerful classical nova explosion that occurred probably a few
thousand years ago.
The image combines data gathered from the far-ultraviolet and
near-ultraviolet detectors on NASA's Galaxy Evolution Explorer on Jan. 25,
2004. The orbiting observatory first began imaging Z Cam in 2003.
Z Cam is the largest white object in the image, located near the center.
Parts of the shell are seen as a lobe-like, wispy, yellowish feature below
and to the right of Z Cam, and as two large, whitish, perpendicular lines
on the left.
Z Cam was one of the first known recurrent dwarf nova, meaning it erupts
in a series of small, "hiccup-like" blasts, unlike classical novae, which
undergo a massive explosion. That's why the huge shell around Z Cam caught
the eye of astronomer Dr. Mark Seibert of Carnegie Institution of
Washington in Pasadena, Calif. - it could only be explained as the remnant
of a full-blown classical nova explosion. This finding provides the first
evidence that some binary systems undergo both types of explosions.
Previously, a link between the two types of novae had been predicted, but
there was no evidence to support the theory.
The faint bluish streak in the bottom right corner of the image is
ultraviolet light reflected by dust that may or may not be related to Z
Cam. Numerous foreground and background stars and galaxies are visible as
yellow and white spots. The yellow objects are strong near-ultraviolet
emitters; blue features have strong far-ultraviolet emission; and white
objects have nearly equal amounts of near-ultraviolet and far-ultraviolet
emission.
