EMBARGOED UNTIL: 9:00 a.m. (EDT) August 24, 1999

PHOTO NO.: STScI-PRC99-32


SYMBIOTIC STAR BLOWS BUBBLES INTO SPACE

A tempestuous relationship between an unlikely pair of stars may have
created an oddly shaped, gaseous nebula that resembles an hourglass
nestled within an hourglass.

Images taken with Earth-based telescopes have shown the larger,
hourglass-shaped nebula. But this picture, taken with NASA's Hubble
Space Telescope, reveals a small, bright nebula embedded in the center
of the larger one (close-up of nebula in inset). Astronomers have dubbed
the entire nebula the "Southern Crab Nebula" (He2-104), because, from
ground-based telescopes, it looks like the body and legs of a crab. The
nebula is several light-years long.

The possible creators of these shapes cannot be seen at all in this Wide
Field and Planetary Camera 2 image. It's a pair of aging stars buried in
the glow of the tiny, central nebula. One of them is a red giant, a
bloated star that is exhausting its nuclear fuel and is shedding its
outer layers in a powerful stellar wind. Its companion is a hot, white
dwarf, a stellar zombie of a burned-out star. This odd duo of a red
giant and a white dwarf is called a symbiotic system. The red giant is
also a Mira Variable, a pulsating red giant, that is far away from its
partner. It could take as much as 100 years for the two to orbit around
each other. 

Astronomers speculate that the interaction between these two stars may
have sparked episodic outbursts of material, creating the gaseous
bubbles that form the nebula. They interact by playing a celestial game
of  "catch": as the red giant throws off its bulk in a powerful stellar
wind, the white dwarf catches some of it. As a result, an accretion disk
of material forms around the white dwarf and spirals onto its hot
surface. Gas continues to build up on the surface until it sparks an
eruption, blowing material into space. 

This explosive event may have happened twice in the "Southern Crab."
Astronomers speculate that the hourglass-shaped nebulae represent two
separate outbursts that occurred several thousand years apart. The jets
of material in the lower left and upper right corners may have been
accelerated by the white dwarf's accretion disk and probably are part of
the older eruption. 

The nebula, located in the Southern Hemisphere constellation of
Centaurus, is a few thousand light-years from Earth.

This image, taken in May 1999, captures the glow of nitrogen gas energized 
by the white dwarf's intense radiation.

These results were presented at the "Asymmetrical Planetary Nebulae II:
From Origins to Microstructures" conference, which took place at the
Massachusetts Institute of Technology, August 3-6, 1999.

Credits: Romano Corradi, Instituto de Astrofisica de Canarias, Tenerife,
Spain; Mario Livio, Space Telescope Science Institute, Baltimore, Md.;
Ulisse Munari, Osservatorio Astronomico di Padova-Asiago, Italy; Hugo
Schwarz, Nordic Optical Telescope, Canarias, Spain; and NASA


NOTE TO EDITORS: For additional information, please contact 
Dr. Mario Livio, STScI, 3700 San Martin Drive, Baltimore, MD 21218,
(phone) 410-338-4439, (fax) 410-338-4767, (e-mail) mlivio@stsci.edu.