Brown dwarf is the coldest star known

Astronomers have discovered the coldest star ever found – and believe it is a “missing link” between suns and planets. The star, known as a brown dwarf, lies only 40 light-years away from Earth, meaning we are seeing it as it was in 1968.

brown dwarfDespite its proximity, the star, dubbed CFBDS0059, shines dimly because its temperature is only around 350 C. It is between 15 and 30 times the size of Jupiter, the biggest planet in the solar system.

The new star was found in the constellation of Cetus, the whale, by an international team of French and Canadian astronomers using giant telescopes in Hawaii and Chile.

The team, who will announce their discovery in the journal Astronomy & Astrophysics, suggest that the star be considered the prototype of a new class of brown dwarfs, to be called Y dwarfs.

Planets such as Jupiter and Saturn are called gas giants because they are not rocky worlds like the Earth. It appears that they may be more closely related to cool stars that failed to burn as intensely as the sun.

The Y dwarf CFBDS0059 looks more like a giant planet than the previously known and hotter L and T classes of brown dwarf. Y dwarfs therefore become the coldest stellar objects known and a missing link between stars and giant planets.

Because of their low mass, the temperatures at the cores of brown dwarfs is not high enough to maintain thermonuclear fusion reactions over a long time.

Unlike the sun, which spends most of its lifetime burning hydrogen and keeping a constant internal temperature, a brown dwarf gets steadily colder and colder after it is formed.

The first brown dwarf was not spotted until 1995. The discovery of an even closer one, 12.5 light-years away, was announced two years ago. Stars and planets are both believed to form from swirling clouds of gas and dust.

Picture: A photo of the field of stars containing the brown dwarf dubbed CFBDS0059. It is the deep red object in the upper part of the photo. (© Canada-France-Brown-Dwarf-Survey 2008).

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Paul Sutherland

Paul Sutherland

I have been a professional journalist for nearly 40 years. I write regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy. I have also authored three books on astronomy and contributed to others.
Paul Sutherland

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Paul Sutherland

I have been a professional journalist for nearly 40 years. I write regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy. I have also authored three books on astronomy and contributed to others.

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