Newborn star discovered at edge of Milky Way Conventional view challenged

August 04, 1993|By Douglas Birch | Douglas Birch,Staff Writer

A team of astronomers from the University of Maryland and Harvard has discovered a newborn star at the edge of our Milky Way galaxy, challenging the conventional view that stars aren't likely to form so far from the gas-rich stellar nurseries found closer to the galaxy's core.

"We've found pretty convincing evidence for star formation out in the periphery of our galaxy," where the key ingredients -- gas clouds and gravity -- are in short supply, said Stuart Vogel of the University of Maryland at College Park, one of the astronomers who made the discovery.

"The astounding thing, for me, is that you could get the large concentrations of the mass needed to make a star" so far from the galaxy's center, he said. "You need enough mass to provide enough gravity to cause [gas] clouds to collapse. Beyond the center, at the edge of the galaxy, there's not very much."

According to an article scheduled to appear in the Aug. 20 edition of Astrophysical Journal Letters, the young star is thought to be a hot, blue supergiant -- a class of objects that are generally 10 to 50 times more massive than the Sun, burn more brightly and exhaust their nuclear fuel more quickly.

Dr. Vogel called it the most distant newborn star ever seen twinkling in the hamburger-patty-shaped collection of perhaps 200 billion stars we call the Milky Way.

The hot blue object was found 90,000 light years from the core of the galaxy, more than three times further from the core than the Sun.

The young giant was discovered near another unusual feature in the galaxy's edge, a cloud of hydrogen molecules about 100 light-years in diameter. (A light-year is the distance light travels in a year, about 5.9 trillion miles).

Astronomers think the cloud provided the key ingredient for the formation of the star -- hydrogen gas. But it's not clear how that gas was compressed to the critical point where gravity could take over the job of star formation.

The Maryland-Harvard team, led by Eugene de Geus while at College Park, searched the hydrogen cloud for young stars last December using a 60-inch telescope at Mount Palomar, Calif. (Dr. de Geus recently joined the faculty of the California Institute of Technology.) The two other team members were Robert Gruendl, a graduate student at College Park and Seth Digel of the Harvard-Smithsonian Center for Astrophysics.

The astronomers found the hot blue star with the aid of a spectrograph built by Dr. Vogel. A spectrograph is a device that can measure the composition of a distant, luminous object, such as a star, by studying the light it emits. The instrument yielded strong evidence that the star was producing the intense radiation associated with newborns.

"The key thing here is that we have the young star, we have the raw material to make a star and we have evidence for the effect of this star on its environment," Dr. Vogel said. "We had everything together in one place. That's what makes a really convincing case that there is star formation out at these distances."

Several other astronomers said they were intrigued by the Maryland-Harvard team's findings. "This is interesting because it has the potential to open a new window on how massive stars form, or how stars form generally," said Philip C. Myers of the Harvard-Smithsonian Center for Astrophysics.

"It was always thought that . . . low-mass stars like our Sun grow like weeds, that they form under variety of conditions, while massive stars are like hot house orchids, they need special conditions to grow," Dr. Myers said. "Maybe what Stu Vogel has shown us is that that is too restricted a view, that massive stars can form under more diverse conditions."

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