EMBARGOED UNTIL: 1:00 p.m. (EST) November 9, 1999

PHOTO NO.: STScI-PRC99-42

THE TRIFID NEBULA: STELLAR SIBLING RIVALRY

This NASA Hubble Space Telescope image of the Trifid Nebula reveals a 
stellar nursery being torn apart by radiation from a nearby, massive 
star. The picture also provides a peek at embryonic stars forming 
within an ill-fated cloud of dust and gas, which is destined to be 
eaten away by the glare from the massive neighbor. This stellar
activity is a beautiful example of how the life cycles of stars like our 
Sun is intimately connected with their more powerful siblings. 

The Hubble image shows a small part of a dense cloud of dust and gas, 
a stellar nursery full of embryonic stars. This cloud is about 
8 light-years away from the nebula's central star, which is beyond the
top of this picture. Located about 9,000 light-years from Earth, the
Trifid resides in the constellation Sagittarius.

A stellar jet [the thin, wispy object pointing to the upper left] 
protrudes from the head of a dense cloud and extends three-quarters of 
a light-year into the nebula. The jet's source is a very young stellar 
object that lies buried within the cloud. Jets such as this are the 
exhaust gases of star formation. Radiation from the massive star at 
the center of the nebula is making the gas in the jet glow, just as it 
causes the rest of the nebula to glow. 

The jet in the Trifid is a "ticker tape," telling the history of one 
particular young stellar object that is continuing to grow as its 
gravity draws in gas from its surroundings. But this particular ticker 
tape will not run for much longer. Within the next 10,000 years the 
glare from the central, massive star will continue to erode the 
nebula, overrunning the forming star, and bringing its growth to an 
abrupt and possibly premature end. 

Another nearby star may have already faced this fate. The Hubble 
picture shows a "stalk" [the finger-like object] pointing from the 
head of the dense cloud directly toward the star that powers the 
Trifid. This stalk is a prominent example of the evaporating gaseous
globules, or "EGGs," that were seen previously in the Eagle Nebula,
another star-forming region photographed by Hubble. The stalk has
survived because at its tip there is a knot of gas that is dense 
enough to resist being eaten away by the powerful radiation. 

Reflected starlight at the tip of the EGG may be due to light from the 
Trifid's central star, or from a young stellar object buried within 
the EGG. Similarly, a tiny spike of emission pointing outward from the
EGG looks like a small stellar jet. Hubble astronomers are tentatively
interpreting this jet as the last gasp from a star that was cut off 
from its supply lines 100,000 years ago. 

The images were taken Sept. 8, 1997 through filters that isolate
emission from hydrogen atoms, ionized sulfur atoms, and doubly ionized
oxygen atoms. The images were combined in a single color composite
picture. While the resulting picture is not true color, it is 
suggestive of what a human eye might see.

Credits: NASA and Jeff Hester (Arizona State University)

NOTE TO EDITORS:  
For additional information, please contact:

Jeff J. Hester, Department of Physics and Astronomy, Arizona State
University, Box 871504, Tempe, AZ 85287-1504, (phone) 480-965-0741,
(e-mail) jhester@asu.edu.