Megan's Blog

In the news this month: the coolest brown dwarf yet

An international team, led by astronomers at the University of Hertfordshire have discovered what may be the coolest sub-stellar body ever found outside our own solar system. Using the United Kingdom Infrared Telescope (UKIRT) in Hawaii, the astronomers have discovered a type of object known as a brown dwarf, smaller than other stars but larger than gas giant planets such as Jupiter. The object, known as SDSS1416+13B, is only visible in infra-red light and is in a wide orbit around a somewhat brighter and warmer brown dwarf known as SDSS1416+13A. This discovery is "the fourth time in three years that UKIRT has made a record breaking discovery of the coolest known brown dwarf, with an estimated temperature not far above 200 degrees Celsius," said the University of Hertfordshire's Dr Philip Lucas.

The light detected from the star is rather unusual, it appears far bluer at near infra-red wavelengths than any other brown dwarf detected so far. A near infrared spectrum, taken with the Japanese Subaru Telescope in Hawaii, showed that it belongs to a class of objects known as T dwarfs, and that is has a lot of methane in its atmosphere but with peculiar features including a big gap at certain wavelengths. Using the Spitzer space telescope to measure its colour at mid-infrared wavelengths,the researchers found that it is also the reddest known brown dwarf at these wavelengths by some margin. A comparison with theoretical models of brown dwarf atmospheres results in a temperature estimate of just 500 Kelvin or 227 degrees Celsius. In comparison, our own Sun has a surface temperature of approximately 6000 Kelvin. Both stars are also lacking in heavy elements, an indication that they may be very old which fits in with the low temperature of the fainter star - fainter stars use up their fuel much slower and can last for many billions of years.

The research has been accepted for publication in the Monthly Notices of the Royal Astronomical Society.

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Ben Burningham, S. K. Leggett, P. W. Lucas, D. J. Pinfield, R. L. Smart, A. C. Day-Jones, H. R. A. Jones, D. Murray, E. Nickson, M. Tamura, Z. Zhang, N. Lodieu, C. G. Tinney, & M. R. Zapatero Osorio (2010). The discovery of a very cool binary system MNRAS arXiv: 1001.4393v1