The largest star in our galaxy appears to be nearing the end of its life and ready to explode with the brightness of billions of suns, according to astronomers at Goddard Space Flight Center and an observatory in Chile.

The massive star, already more than 100 times the brightness of the sun, is about 9,000 light years from earth. The astronomers cannot pinpoint when the star will explode, but it will be "soon" by astronomical standards, probably within 10,000 years. In fact, since it takes 9,000 years for the star's light to reach earth, it may already have exploded.

Dr. Kris Davidson of the University of Minnesota said the last three observances of such an explosion at the end of a star's life occurred in the years 1054, 1572 and 1604. Scientists have never seen a star before it turned into a supernova.

Supernovae are believed to occur when a star has used up its available fuel and collapses under strong gravitational pull, unleashing a tremendous amount of energy.

Called Eta Carinae, the star is in the sky of the Southern Hemisphere and can be seen near the horizon in the southern United States. In its last weeks, it may be as bright as the planet Venus in the evening sky or even bright enough to be seen in the daytime.

In work funded by the National Science Foundation, the chief discovery by the astronomers was that about 150 years ago Eta Carinae spat out hot gas and that gas contained less carbon and oxygen and far more nitrogen than a younger star would.

Davidson explained that the nitrogen probably was produced by nuclear reactions at the core of the star over many millions of years. It also takes much time for the nitrogen from these reactions to migrate to the surface of the star and escape.

Since both events have occurred, Eta Carinae is thought very likely to be near its end.

Davidson, Nolan Walborn of Cerro Tololo Inter-American Observatory in Chile and Goddard's Theodore Gull published their findings in the current issue of the Astrophysical Journal.