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Title    : Symbiotic Star Blows Bubbles into Space
Author : Office of Public Outreach -- [email protected]
Date    :


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

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

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

The Space Telescope Science Institute is operated by the Association of
Universities for Research in Astronomy, Inc. (AURA), for NASA, under contract
with the Goddard Space Flight Center, Greenbelt, MD. The Hubble Space
Telescope is a project of international cooperation between NASA and the
European Space Agency (ESA).





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