Congratulations to my Imperial College Astrophysics colleagues Steve Warren and Dan Mortlock who have been in the news lately for their discovery of the coldest brown dwarf yet found. A brown dwarf is not quite a star, but a ball of gas just too light to force its hydrogen gas into nuclear fusion reactions. Instead it glows weakly as the gas slowly condenses, releasing gravitational potential energy in the form of heat. Brown dwarfs have a mass between roughly ten times the mass of Jupiter, below which they can form a rocky core and are classed as a planet, and one-tenth the mass of the sun, above which they can ignite fusion reactions.
Steve, Dan and their colleagues have found this object, endearingly called ULAS J0034-00, using the UKIDSS (UKIRT Infrared Deep Sky Survey) survey. Infrared (long wavelength) surveys are ideal for finding cold objects like brown dwarfs — warmer, bigger objects glow in the shorter optical and ultraviolet wavelengths. They’re also ideal for finding very distant galaxies, whose optical and UV glows have been redshifted to the infrared. Indeed, one of the other major goals of the survey is to try to find the most distant objects out there — and hence the earliest to have formed.