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Astronomers Investigating Intriguing And Hard to Detect "Brown Dwarfs"

By Kathy Sawyer
The Washington Post

Astronomers reported yesterday new evidence that the universe is populated with dim, intriguing objects too small to be stars but too large to be planets.

At least some of them are loners, and one of them in some ways resembles Saturn's moon Titan.

These objects - known as brown dwarfs - are stubbornly difficult to detect, but they have finally begun to emerge from their cloak of darkness, as technologies improve. Several likely candidates have been discovered recently, but the first "unambiguous detection" was confirmed only late last year, orbiting a star 18 light years from Earth called Gliese 229.

This week, researchers reported at a meeting in Liverpool, England, that they have "unequivocally" detected the first brown dwarfs ever found in complete isolation - that is, not in orbit around a star or even grouped in a star cluster like two found in the Pleiades recently.

Brown dwarfs are believed to be failed stars, born with insufficient mass to build the high temperatures required to trigger the thermonuclear fusion that gives stars their shine. Astronomers consider an understanding of these objects crucial to the search for planets around other stars.

The new brown dwarfs are all relatively close - within 150 light years of the sun. Their detection "raises the real possibility that there may be many more," said Hugh Jones of Liverpool John Moores University, who led the discovery team. They used a computerized measuring machine known as COSMOS, in Edinburgh, to search for brown dwarf candidates in photographic plates taken with the United Kingdom's Schmidt telescope in Australia.

One of these brown dwarfs, known only as "296A," lies in the southern sky on the border between the constellations Sculptor and Phoenix, the researchers said.

"It may be only 60 times more massive than the planet Jupiter" or about 6.5 percent of the sun's mass, they reported. It seems to have a surface temperature of about 5,000 degrees Fahrenheit and a luminosity about one thousandth that of the sun.

Under casual observation, this object looks like a normal star similar to the sun, though less massive, cooler and red instead of yellow.