Brown Dwarf Hunt Hits Record Low

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Brown dwarfs are curious objects. Although they can weigh up to 80 Jupiter masses, they are too small to be called stars yet too big to be called planets. Until the late 1980′s they were purely theoretical objects.

However, as our observational capabilities improved — allowing astronomers to look deeper into space, detecting cooler objects — many of these “failed stars” (or could they be called “successful planets”?) were found to be floating around our galaxy.

Now a team of astronomers, using the United Kingdom Infrared Telescope (UKIRT) in Hawaii, may have spotted the coolest brown dwarf yet.

“This looks like being the fourth time in three years that the UKIRT has discovered made a record breaking discovery of the coolest known brown dwarf, with an estimated temperature not far above 200 degrees Celsius,” said Dr Philip Lucas at the University of Hertfordshire’s School of Physics, Astronomy and Mathematics, UK.

200 degrees Celsius (or nearly 400 degrees Fahrenheit) is only twice as hot as the cup of tea I have cooling on my desk, so it is little wonder brown dwarfs are known as “sub-stellar” objects. (For an object to be “stellar,” it needs to be a star, burning fuel through nuclear fusion. Brown dwarfs are too small to do this for long periods of time.)

The previous “Coolest Sub-Stellar Object” prize went to a brown dwarf called Wolf 940B, located 40 light years from Earth. Wolf 940B was measured to have a surface temperature of 300 degrees Celsius by Australian astronomers.

The cold SDSS1416+13B and its hot companion brown dwarf SDSS1416+13A (left image is from the UKIRT telescope and the right image from the Subaru telescope).

This new brown dwarf (with the seriously un-sexy name SDSS1416+13B) is orbiting another, hotter brown dwarf (called — you guessed it — SDSS1416+13A). The pair, like Wolf 940B, are located in our cosmic back yard between 15 and 50 light years from Earth.

SDSS1416+13B is so cool that it emits very little visible light and can only be observed in infrared wavelengths. Although the fact it appears very cool is exciting astronomers, there’s another factor to consider.

Follow-up observations of this object by NASA’s Spitzer Space Telescope noticed that SDSS1416+13B is the reddest brown dwarf discovered to date.

“We have to be a bit careful about this one because its colours are so different than anything seen before that we don’t really understand it yet,” added Lucas. “Even if it turns out that the low temperature is not quite record breaking, the colours are so extreme that this object will keep a lot of physicists busy trying to explain it.”

Scientists think the strange color of the brown dwarf and its low temperature suggests that it is lacking heavy elements and therefore very old. These factors make SDSS1416+13B a very interesting object to study as it provides valuable information about the evolution of these mysterious objects.

Source: University of Hertfordshire.

Image (top): Artist’s impression of a brown dwarf (NASA/ESA/G Bacon (STScI))