10-22-2011, 02:19 PM
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Scientists Find Coldest Ever Star
| |The temperature of the surface is like a hot summer's day in Arizona or Seville - and would be quite pleasant for humans. It's the coldest object ever photographed outside our solar system.
But WD 0806-661 B is not a planet - it's a very small star. Its mass is just six to nine times the gas giant Jupiter.
Artists impression of what the brown dwarf discovered with the Nasa spitzer telescope would look like - the tiny, cold star orbits a white dwarf, the burnt-out remnant of a star like our sun:
Penn State Associate Professor of Astronomy and Astrophysics Kevin Luhman, who discovered the object said, 'It is a very small star with an atmospheric temperature about as cool as the Earth's.'
The astronomers used Nasa's Spitzer space telescope - the most sensitive space telescope on Earth - to find the cold star, scanning 600 near-earth stars for objects orbiting them. Infrared telescopes are used because cold objects 'shine out' brightly in the images. The record-breaking star is 63 million light years from Earth and orbits a dense, collapsed 'white dwarf' star.
The star is a brown dwarf - and formed, like other stars, out of a cloud of dust and gas.
But because it failed to accumulate enough mass from the dust cloud, the thermonuclear reaction that 'lights up' normal stars fail to ignite.
The new brown dwarf's surface is between 27 and 80 degrees centigrade - so in places, it's a temperature humans might enjoy.
The new brown dwarf has a surface temperature between 27 and 80 degrees centigrade, and orbits a white dwarf star:
Artist's impression of a brown-dwarf object (left foreground) orbiting a distant white dwarf, the collapsed-core remnant of a dying star:
Ever since brown dwarfs first were discovered in 1995, astronomers have been trying to find new record holders for the coldest brown dwarfs - the objects are seen as valuable laboratories to help us understand the atmospheres of extrasolar planets with Earth-like temperatures.
Astronomers have named the brown dwarf ‘WD 0806-661 B’. It orbits the ‘white dwarf’ core of a star . The white dwarf would have shone like our sun until its outer layers were expelled into space in the final stages of a star's life.
‘The distance of this white dwarf from the Sun is 63 light-years, which is very near our solar system compared with most stars in our galaxy,’ Luhman said.
The orbit of the brown dwarf is huge, about 2,500 times the distance between Earth and the sun.
Luhman and his colleagues presented this new candidate for the coldest known brown dwarf in a paper published in spring 2011, and they now have confirmed its record-setting cool temperature in a new paper that will be published in the Astrophysical Journal.