Hopkins-Caltech team says it has found brown dwarf Proof of existence of the starlike objects has eluded astronomers

November 30, 1995|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

Astronomers searching among our nearest stellar neighbors say they have found the first unambiguous example of a "brown dwarf" -- a long-theorized, but elusive starlike object that never grew large enough to ignite nuclear fusion and shine like a star.

The object was found by a team from the Johns Hopkins University and the California Institute of Technology. It is orbiting a red star called Gliese 229 about 19 light years -- 112 trillion miles -- from Earth.

Gliese 229 is too dim to be seen with the naked eye. But it is near the constellation Lepus, just below Orion in the winter sky.

"This is probably a definitive case for a brown dwarf," said Dr. Stephen P. Maran, senior staff scientist at the Goddard Space Flight Center's Laboratory for Astronomy and Solar Physics in Greenbelt.

Scientists have been searching for brown dwarf stars for decades, hoping they might prove common enough to account for much of the unseen "missing mass" needed to explain the behavior of the bright objects in the night sky.

Caltech's Dr. Shrinivas Kulkarni said his team searched 100 nearby stars before finding one brown dwarf. With that rarity, he said, "I don't think we're going to find the answer to dark matter there."

Several possible brown dwarf sightings have been reported in recent months, but none was considered conclusive until now.

The find provides scientists with valuable information they can use in their search for planetary systems orbiting nearby stars. Specifically, the data should help them to distinguish between brown dwarfs and massive, Jupiterlike planets.

Gliese 229B, in fact, looks a great deal like Jupiter. "This is the first time we have ever observed an object beyond our solar system which possesses a spectrum that is astonishingly just like that of a giant gas planet," said Dr. Kulkarni.

That spectrum revealed Gliese 229B to be rich in methane, like Jupiter. Stars with nuclear fires are too hot for methane to form. The presence of the gas on Gliese 229B is seen as definitive proof that Gliese 229B has no nuclear fire and is a brown dwarf.

About 250,000 times dimmer than Earth's sun, it is the faintest object ever seen orbiting another star.

Gliese 229B also proved to be nearly the same diameter as Jupiter -- about 80,000 miles wide. But it is 20 to 50 times more massive and much hotter -- about 1,300 degrees, pushing it well beyond consideration as a planet.

It is thought to be at least 4 billion miles from its star -- about the distance from the sun to Pluto.

The key difference between brown dwarf stars and planets lies in their origins, scientists say.

Planets form by the agglomeration of dust and gas circling a star. They start as small rocky or icy balls, and grow like snowballs as they gain mass and attract more material.

Brown dwarfs, like normal stars, start big as a huge cloud of hydrogen, which gradually collapses into a compact ball. But unlike normal stars, brown dwarfs never get big or hot enough to ignite and sustain the nuclear fusion that makes a real star shine.

Gliese 229B was spotted from the Palomar Observatory in California by a team that included Hopkins astronomer and former astronaut Dr. Sam Durrance, Hopkins astronomer David Golimowski and Caltech astronomers Dr. Kulkarni, Ta--i Nakajima, Keith Matthews and Ben Oppenheimer.

The observation was confirmed less than two weeks ago by the Hubble Space Telescope, with the help of Dr. Chris Burrows of the Space Telescope Science Institute in Baltimore.

The discovery of Gliese 229B, reported today in the journal Nature, and tomorrow in the journal Science, was made possible by a "coronagraph" designed and invented at Hopkins by Dr. Durrance. The device reduced the glare from Gliese 229B's star.

Images of Gliese 229B are available on the Internet at: http:// www.stsci.edu/pubinfo/PR/95 /48.html

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