NASA Mission Finds Link Between Big and Small Stellar Blasts(Forwarded)

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
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http://www.jpl.nasa.gov

Jane Platt 818-354-0880
Jet Propulsion Laboratory, Pasadena, Calif.

March 7, 2007

NEWS RELEASE: 2007-023

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 Evolution Explorer.

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.

"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 time."

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.

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."

More information on the Galaxy Evolution Explorer is online at
http://www.nasa.gov/galex
and
http://www.galex.caltech.edu

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 mission.