Hubble detects star with the energy of 10 million suns Vast dust clouds hid Milky Way's brightest


Try to imagine a star so big that it would fill all of the solar system within the orbit of Earth, which is 93 million miles from the sun. A star so turbulent that its eruptions would spread a cloud of gases spanning four light-years, the distance from the sun to the nearest star. A star so powerful that it glows with the energy of 10 million suns, making it the brightest ever observed in our galaxy, the Milky Way.

A star so big and bright should be unimaginable, according to some theories of star formation. But there it is, near the center of the Milky Way, long hidden from the human eye by vast dust clouds and its magnitude only now revealed by the Hubble Space Telescope, using a camera sensitive to the infrared light that penetrates the clouds.

The detection of the luminous star, about 25,000 light-years from Earth in the direction of the constellation Sagittarius, was announced yesterday by the Space Telescope Science Institute in Baltimore and the University of California at Los Angeles. The infrared photograph was taken and analyzed by a team of astronomers led by Dr. Don Figer and Dr. Mark Morris of the university.

"This star may have been more massive than any other star, and now it is without question still among the most massive," Figer said. "Its formation and life stages will provide important tests for new theories about star birth and evolution."

Dr. Bruce Margon, an astronomer at the University of Washington in Seattle, said the discovery demonstrated the ability of the Hubble telescope's near-infrared camera and multiobject spectrometer, an instrument installed last year by visiting astronauts, to probe the Milky Way's central regions. Dust clouds there had left astronomers working in a virtual fog. The dust absorbs the visible light of stars, even those as bright as the one just identified.

As a result, "we know less about the center of our own galaxy than we do about the center of other much more distant galaxies," Margon said.

The presence of a presumably mammoth star in that dusty region was first noted early in this decade by ground-based infrared telescopes. In research for his doctorate in astronomy, Figer found reasons to suspect that the star was especially powerful and that its "past eruptive stages" might have created the nebula of dust and gas around it.

The Hubble findings not only revealed the full magnitude of the star but also confirmed that its eruptions had produced the extensive nebula. Astronomers said the shape of the nebula reminded them of a pistol, and named its source the Pistol Star.

From the star's brightness and prodigious output of gases, astronomers have drawn conclusions about its short and brilliant career. It probably formed 1 million to 3 million years ago, a brief time in cosmic history. It may have weighed up to 200 times the mass of the sun before consuming and shedding so much of its mass in violent eruptions.

Figer and Morris said the Pistol Star was so massive when it was born that it brought into question current thinking about how stars were formed. Stars take shape within huge dust clouds when interstellar gases contract under their own gravity, eventually condensing into hot clumps that ignite the hydrogen fusion process.

"We don't really understand the details of how stars form out of diffuse interstellar gas," Margon said. "We don't know what determines the size of the proto-stellar clumps, but there must be some upper limit to the potential mass of a viable star."

Morris of UCLA said, "Current evidence leads us to believe that the star formation process near the center of the galaxy may favor stars much more massive than our modest sun."

Pub Date: 10/08/97

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