PARIS: Scientists have located the coldest brown dwarf star ever observed, an important missing link among these celestial bodies that are half-planet, half-star, according to a study released yesterday.
A team of French and Canadian astronomers made the discovery using two powerful telescopes in Hawaii and one in Chile, according to the study, to be published this month in the European journal Astronomy and Astrophysics.
The brown dwarf – poetically named CFBDS J005910.83-011401.3 – is sizzling hot by Earth standards, with a surface temperature of some 350°C. But it is far colder than any brown dwarf seen to date and will probably prompt the creation of a new category of heavenly bodies.
Categories of dwarfs
So-called "L dwarfs" have temperatures of 1200 to 2000°C, and are enveloped in clouds of dust and aerosols in their high atmosphere; "T dwarfs" are cooler, and their atmospheres contain methane. But CFBDS0059 – as the new star is known among astronomers – is by far the coldest observed to date.
Because it contains ammonia and has a much lower temperature than L and T dwarfs, CFBDS0059 is the likely prototype of a new class to be called "Y" dwarfs. It constitutes a kind of "missing link" between small stars and giant planets, the study says.
The discovery has important implications for the study of extra-solar planets, which are very hard to observe because the light they cast is rendered faint by the far stronger light generated by their parent stars.
Brown dwarfs are easier to observe because they are isolated bodies, meaning they do not orbit another star.
Shedding light on large planets
Because CFBDS0059 is especially similar to large planets in atmosphere and temperature, scientists will be able to learn much about hard-to-see planets by studying its atmosphere and behaviour.
CFBDS0059 is about 15 to 30 times the mass of Jupiter, the largest planet in our Solar System, and is located some 40 light years away. In contrast to a star like our Sun, which burns hydrogen to maintain a constant internal temperature, brown dwarfs gets colder and colder after having been formed.
The first brown dwarfs were detected in 1995. While sharing certain properties with giant planets, there are several major differences. In brown dwarf atmospheres, water is always in gaseous state, while in giant planets it condenses into water ice. And while ammonia has never before been detected in the brown dwarf near-infrared spectra, it is a major component of Jupiter's atmosphere.
