NASA Telescope Catches Surprise Ultraviolet Light Show (GALEX)

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
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http://www.jpl.nasa.gov

Whitney Clavin (818) 648-9734
Jet Propulsion Laboratory, Pasadena, Calif.

News release: 2005-088 May 31, 2005

NASA Telescope Catches Surprise Ultraviolet Light Show

It was a day like any other for a nearby star named GJ
3685A - until it suddenly exploded with light. At 2 p.m.
Pacific time on April 24, 2004, the detectors on NASA's
Galaxy Evolution Explorer ultraviolet space telescope
nearly overloaded when the star abruptly brightened by a
factor of at least 10,000. After the excitement was over,
astronomers realized that they had just recorded a giant
star eruption, or flare, about one million times more
energetic than those from our Sun.

Findings on this intriguing event were presented today at
the 206th meeting of the American Astronomical Society in
Minneapolis, Minn. Movies based on images of the flare are
available online at
http://www.nasa.gov/centers/jpl/missions/galex.html and
http://www.galex.caltech.edu/ .

This dramatic flare is just one of many serendipitous
discoveries made by the Galaxy Evolution Explorer since its
2003 launch.

Though the telescope was originally designed to spot
galaxies, it has repeatedly witnessed a sky flickering with
ultraviolet flares, bursts and fast-moving streaks. While
the flares and bursts are from different types of stars,
the streaks are asteroids, satellites or possibly space
debris floating across the telescope's field of view.

The findings have led astronomers to conclude that the
ultraviolet sky, once thought to be a quiet backdrop for
viewing galaxies, is, in fact, a rather festive place.

"We had no idea that the ultraviolet sky would be filled
with so many things that go bump in the night," said Dr.
Barry Welsh, University of California, Berkeley, co-
discoverer of some of the flares. "All of these objects are
a bonus to astronomers, since the observations come free
when the telescope is aimed at distant galaxies."

"I was surprised by how often we have observed stellar
flares and by the amazing size of some of them," said Dr.
Chris Martin, principal investigator of the Galaxy
Evolution Explorer, California Institute of Technology,
Pasadena. "Nature rarely disappoints us."

So far, the Galaxy Evolution Explorer has recorded 84 bonus
astrophysical events occurring on flaring stars, binary
stars called dwarf novae, and pulsating stars, as well as
countless pieces of space debris. These data are already
being collected into public databases for other astronomers
to study. For example, astronomers are using the new set of
flare stars to test their flare theories.

The Galaxy Evolution Explorer is surveying the entire sky
at ultraviolet wavelengths for clues to how the earliest
galaxies evolved into mature galaxies like our own Milky
Way. To detect these early, faint galaxies, the telescope
was outfitted with specialized cameras that allow the
arrival of each photon of ultraviolet light to be timed
with a precision of about a microsecond.

"The telescope's detectors have provided an unprecedented
time resolution of these astrophysical events," said Welsh.
"Now, we can say what happens during each one-hundredth of
a second of a flare event. That's better information than
most video cameras have when they take slow motion shots of
athletes."

A preliminary analysis of the enormous flare witnessed by
the Galaxy Evolution Explorer around GJ 3685A - the largest
ever recorded in ultraviolet light - shows that the
mechanisms underlying these stellar eruptions may be more
complex than previously believed. Evidence for the two most
popular flare theories was found.

Flares are huge explosions of energy stemming from a single
location on a star's surface. They happen regularly on many
types of stars, though old, small "red dwarf" stars like
GJ 3685A tend to experience them most frequently and
dramatically. These stars, called flare stars, can erupt as
often as every few hours, and with an intensity far greater
than flares from our Sun. One of the reasons astronomers
study flare stars is to gain a better picture and history
of flare events taking place on the Sun.

Caltech leads the Galaxy Evolution Explorer mission and is
responsible for science operations and data analysis.
NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages
the mission and built the science instrument. The mission
was developed under NASA's Explorers Program managed by the
Goddard Space Flight Center, Greenbelt, Md. South Korea and
France are the international partners in the mission.

For more information about the Galaxy Evolution Explorer,
visit http://www.galex.caltech.edu/ .


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