PASADENA, Calif. - Astronomers working on an effort to catalog the heavens report that they have imaged the coolest body ever found outside our solar system, a type of brown dwarf that could be as abundant as the stars above.
The temperature of the object, larger than a typical planet but smaller than a star, is a relatively frosty 900 degrees Fahrenheit (500 degrees Celsius). By comparison, the temperature of the sun's surface is 10,000 degrees Fahrenheit (5,500 degrees Celsius).
"That makes it the coolest star-like object ever imaged beyond our solar system," said Davy Kirkpatrick of the object, dubbed Gliese 570-D. Kirkpatrick is senior staff scientist at the Infrared Processing and Analysis Center (IPAC) on the Caltech campus in Pasadena, California.
The Jupiter-sized brown dwarf, essentially a failed star too small to ignite a nuclear reaction in its core, lies just 18 light-years from Earth as part of a previously known triple-star system in the constellation Libra. (A light-year is 5.88 trillion miles.)
In an interview prior to announcing the discovery at the 195th meeting of the American Astronomical Society in Atlanta, fellow discoverer Adam Burgasser said Gliese 570-D was the 12th such object found by the 2-Micron All Sky Survey (2MASS) since 1995.
Astronomers have tentatively called the new objects methane brown dwarfs because of the presence of the gas in their spectra. Methane is typical of giant planets like Jupiter, but never appears in stars or in most other brown dwarfs, both of which are far too hot.
"These things are so cool, you can have chemistry," said Burgasser, a Caltech graduate student in physics whose doctoral dissertation focuses on the objects.
All told, astronomers worldwide have found some 15 of the methane brown, or "T," dwarfs -- most in the last six months.
"It's been busy," Burgasser said.
David Golimowski, a co-discoverer of the first methane brown dwarf, Gliese 229-B, said the cool, dim objects could be as plentiful as the more brilliant stars that stud the skies in our stellar neighborhood.
"There could be one for every star," said Golimowski, an associate research scientist at Johns Hopkins University.
Astronomers could reasonably expect to find even cooler brown dwarfs in the future, although search methods are biased toward finding hotter and thus brighter objects.
Gliese 570-D cropped up in a photograph made in 1998 as part of 2MASS's efforts to image the entire sky at near-infrared wavelengths. Burgasser said they later confirmed its was a brown dwarf by taking its spectral fingerprint with a 4-meter telescope at the Cerro Tololo Interamerican Observatory in Chile.
The 2MASS project, a collaborative effort between the University of Massachusetts and IPAC, expects to publicly release a catalog of about half the sky -- with almost 200 million objects -- this year.
Burgasser and Golimowski both said the trick now is to understand how the methane brown dwarfs so far imaged might differ.
"We are sort of hard-pressed to discover what's different about them," Golimowski said.
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