This artist's concept shows the dimmest star-like bodies currently known
-- twin brown dwarfs referred to as 2M 0939. The twins, which are about
the same size, are drawn as if they were viewed close to one of the bodies.
Brown dwarfs are neither planets nor stars. They form like stars out of
collapsing clouds of gas and dust, but they don't have enough mass to
ignite nuclear burning in their cores and become full-blown stars. They
are similar to Jupiter in that they are cool balls of gas, but they are
warmer and heavier. Astronomers say that the universe is littered with
these cosmic misfits, but because they are so dim, they are hard to find.
NASA's Spitzer Space Telescope is fitted with heat-seeking infrared eyes,
which allow it to detect the minute glow of cool objects like brown
dwarfs. Data from Spitzer and the Anglo-Australian Observatory in
Australia together reveal that both of the brown dwarfs making up 2M 0939
share the title of dimmest known brown dwarfs. Their atmospheres are also
among the coolest known for any brown dwarf (565 to 635 Kelvin or 560 to
680 degrees Fahrenheit).
The term "brown dwarf" comes from the fact that these objects cool and
change over time, and therefore do not have a definitive color. The 2M
0939 brown dwarfs, if we could see them directly, would have a dark
magenta hue due to their cool temperatures and the presence of water,
methane and ammonia gases in their atmospheres.
2M 0939's full name is 2MASS J09393548-2448279 after the partly
NASA-funded infrared mission, the Two Micron All Sky Survey, or "2MASS,"
which first detected the object in 1999.