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Watching a young star eat.

Like proud parents showing off their baby, astronomers last month published the first pictures of a newborn star eating. Still swaddled inside a gas cloud, the fledgling star grows more massive by using gravity to draw in cold gas and dust from the envelope of material surrounding it.

The images provide compelling evidence for the classical model of how newborn stars accrete matter, the same process our own sun underwent soon after its birth.

Residing in the gas cloud known as Bok Globule B335, the infant star lies behind a veil of dust and can't be seen in visible light. Instead, astronomers used radio telescopes to measure the velocity of matter raining down on the star.

"It's a beautiful confirmation of [a key step in] star formation," says coinvestigator William D. Langer of NASA's Jet Propulsion Laboratory in Pasadena, Calif. He notes that star formation has four stages. First, gravity pulls together a cloud of gas, creating a compact ball--a protostar--surrounded by a gaseous envelope. Then a disk of material forms around the protostar. As it snares matter falling onto the disk, the protostar grows bigger. Finally, it may develop a jet of gas or wind that eventually stops mass from accumulating.

Langer and his colleagues tracked the infalling gas by measuring the velocity of a trace component, dicarbon monosulfide, which emits radio waves. Combining data from the Very Large Array radio telescope near Socorro, N.M., and NASA's 70-meter single-dish antenna in Goldstone, Calif., the astronomers found that at some spots, the infalling gas moves toward Earth, while at others it recedes at the same speed. Gas raining down on a central star from all sides of a spherical envelope would create such a velocity pattern.

Langer and JPL colleagues Thangasamy Velusamy and Thomas B.H. Kuiper report their study in the Oct. 1 Astrophysical Journal Letters.

Langer notes that the protostar is already about 150,000 years old and will probably double its age before it reaches maturity and takes off the feedbag. Intriguingly, the astronomers detected the dicarbon monosulfide gas only in the outer, coldest part of the envelope. Either the gas condenses on dust grains in the inner, denser part of the envelope or some chemical process transforms the molecule, Langer notes. Similar activity may have taken place in the outer region of the envelope around the infant sun. Icy material from this area coalesced onto a disk to form Pluto and the other outer planets.

Langer told Science News that in the last few weeks, his team has observed activity in the inner part of the star's envelope by monitoring another trace compound, carbon monosulfide, at the Owens Valley Radio Observatory near Big Pine, Calif.
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Publication:Science News
Article Type:Brief Article
Date:Nov 18, 1995
Words:450
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