Brown dwarfs, too tiny to be called stars but too massive to be called planets, strain the everyday language of astronomy with their peculiar characteristics.
In a way, they are like miniscule stars, originally formed from a condensing cloud of gas and dust.
But because they have such low mass, gravity never contracts them enough to raise their core temperature high enough to ignite the thermonuclear reaction known as fusion that powers all stars.
Brown dwarfs were long theorized by astronomers but only discovered in 1995, with the discovery of Gliese 229B.
This most recent discovery by scientists at the European Southern Observatory is significant because of the faintness of the object. Not only was it farther from Earth than any previously discovered methane brown dwarf, but it is of the coolest class of brown dwarfs.
Methane brown dwarfs, as they are called, are so cool that they don't destroy their methane fuel, which is obliterated at 1227 degrees Celsius.
The object discovered by the ESO has a temperature of around 700 degrees Celsius (1652 degrees Fahrenheit).
Not yet formally named, the object was found in a region of the sky called Deep Field, long studied by astronomers as a window to very distant galaxies.
The astronomers were testing their telescopes to see how far they could see into the sky when they came across the object, said ESO spokesman Claus Madsen.
"It certainly seems to be a coincidence that it was discovered at all," Madsen said.
The scientists, too, have said the odds were against the discovery.
"The chances of identifying a rare object like this in such a restricted area are very small," the scientists wrote in their public announcement of the discovery on August 18. "The astronomers readily admit that they must have been very lucky."
But it may have been more than chance.
"It is now of high interest," the astronomers write, "to test if this first discovery was just extremely lucky, or if the space density of these extreme objects is in fact much higher than expected."
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