NASA Mission Finds Link Between Big and Small Stellar Blasts
Proof that certain double star systems can erupt in full-blown explosions and then continue
to flare up with smaller bursts has been spotted by the ultraviolet eyes of NASA's Galaxy
The finding bolsters a 20-year-old theory that suggests such double-star, or binary systems,
should eventually undergo both types of explosion, rather than just one or the other. It
implies the systems probably cycle between two blast types, hiccupping every few weeks with
small surges until the next giant outburst about 10,000 years later.
Image right: This composite image shows Z Camelopardalis, or Z Cam, a double-star system featuring a collapsed, dead star, and a companion star, as well as a ghostly shell around the system. Image credit: NASA/JPL-Caltech
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"The new images are the strongest evidence yet in favor of the cyclic evolution of these
binary stars," said Dr. Mike Shara of the American Museum of Natural History, New York, lead
author of a new paper that details the finding in the March 8 issue of the journal Nature.
"It's gratifying to see such strong evidence for this theory finally emerge after all this
The new discovery centers around Z Camelopardalis (Z Cam), a stellar system that astronomers
have long known to be a cataclysmic binary - a system featuring a collapsed, dead star, or
white dwarf, which behaves like a vampire sucking hydrogen-rich matter from a companion
star. The stolen material forms a rotating disk of gas and dust around the white dwarf.
Astronomers divide cataclysmic binaries into two classes - dwarf novae, which erupt in
smaller, "hiccup-like" blasts, and classical novae, which undergo huge explosions.
Classical novae explosions are 10,000 to a million times brighter than those of dwarf novae,
and they leave behind large shells of shocked gas.
About 530 light years from Earth, Z Cam was one of the first dwarf novae ever detected. For
decades, observers have watched the system hiccup with regular outbursts. It brightens about
40-fold every 3 weeks or so, when an instability causes some of the material drawn by the
stellar vampire to crash onto the white dwarf's surface.
Image left: This enhanced image from the far-ultraviolet detector on NASA's Galaxy Evolution Explorer shows a ghostly shell of ionized gas around Z Camelopardalis, a binary, or double-star system featuring a collapsed, dead star known as a white dwarf, and a companion star. Image credit: NASA/JPL-Caltech
+ Full image and caption
Theory holds that Z Cam and other recurring dwarf novae should eventually accumulate enough
matter and pressure from their swirling disks of hydrogen to trigger gigantic hydrogen bombs
- classical novae explosions. But no one had found definitive evidence that a binary had
experienced both types of blasts until the Galaxy Evolution Explorer's observations of Z
Cam, which began in 2003.
That's when Dr. Mark Seibert of the Carnegie Institution of Washington in Pasadena, Calif.,
serendipitously noticed a never-before-seen arc and linear features surrounding Z Cam in
imaging data the Galaxy Evolution Explorer collected during its Survey of Nearby Galaxies.
The features indicated the presence of a massive shell around Z Cam - evidence that the
dwarf nova had in fact undergone a classical nova explosion a few thousand years ago.
Previous observations had failed to reveal the massive shell because it cannot be easily
detected at optical wavelengths. It is, however, easily seen at the ultraviolet wavelengths
detected by the Galaxy Evolution Explorer.
"You could actually see it immediately," Seibert said. "But we had to convince ourselves
that we were really seeing a nova remnant."
Narrowband images from Kitt Peak National Observatory near Tucson, Ariz., Palomar
Observatory near San Diego, Calif., and the Wise Observatory near Mizpe Ramon, Israel, along
with optical spectroscopic measurements made at the Lick Observatory near San Jose, Calif.,
by other team members confirmed that the structures detected in the Galaxy Evolution
Explorer imaging data were indeed a massive shell of gas surrounding Z Cam.
The authors of the new paper write that Z Cam's classical nova explosion must have been
quite spectacular. "During that eruption," they write, "it must have become, for a few days
or weeks, one of the brightest stars in the sky."
Caltech leads the Galaxy Evolution Explorer mission and is responsible for science
operations and data analysis. NASA's Jet Propulsion Laboratory, also in Pasadena, manages
the mission and built the science instrument. JPL is a division of Caltech. The Galaxy
Evolution Explorer mission was developed under NASA's Explorer Program managed by the
Goddard Space Flight Center, Greenbelt, Md. Researchers sponsored by Yonsei University in
South Korea and the Centre National d'Etudes Spatiales (CNES) in France collaborated on this
Media contact: Jane Platt (818) 354-0880
Jet Propulsion Laboratory, Pasadena, Calif.