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article imageAstronomers discover freezing cold star in Earth’s backyard

By Robert Myles     Apr 30, 2014 in Science
Pasadena - The recent discovery of a brown dwarf star by astronomers using NASA's Wide-field Infrared Survey Explorer (WISE) and Spitzer Space Telescope is remarkable in two respects.
Not only is the newly discovered star relatively close to Earth, but the star’s surface temperatures are sub-zero.
The newly found star has been designated WISE J085510.83-071442.5 and lies just 7.2 light-years away — a stone’s throw in cosmic terms. That makes the new brown dwarf the fourth closest star system to our Sun. Our nearest neighbor, the Alpha Centauri triple star system, lies just over 4 light-years distant.
The new brown dwarf is also a very cold object; its surface temperature is in the range minus 48 to minus 13 degrees Celsius. That makes it colder than the North Pole. The sub-zero temperature also made the star extremely difficult to spot. Previous record holders for coldest brown dwarfs, discovered by WISE and Spitzer, were about room temperature.
WISE was able to track down WISE J085510.83-071442.5’s existence as it surveyed the entire sky twice in infrared light, viewing some areas three times. Viewed in the visible light spectrum, cool objects like brown dwarfs can be invisible. But in infrared light, their feeble glow stands out.
The new star’s proximity to Earth also played a part in its discovery. The closer an object is to Earth, the more it appears to move in images sometimes taken months apart.
Commenting on the newly discovered star, Kevin Luhman, an astronomer at Pennsylvania State University's Center for Exoplanets and Habitable Worlds, said, “It's very exciting to discover a new neighbor of our solar system that is so close. And given its extreme temperature, it should tell us a lot about the atmospheres of planets, which often have similarly cold temperatures."
Brown dwarf stars start off their stellar existence much like other stars as collapsing balls of gas. But unlike star’s like our Sun, brown dwarfs lack sufficient mass for nuclear fusion — the process of converting hydrogen into helium. As a result, brown dwarfs don’t radiate starlight.
Scientists estimate the size of WISE J085510.83-071442.5 at between 3 and 10 times the mass of Jupiter. Because the brown dwarf’s mass is so modest, there’s a possibility that the ‘star’ is in fact a gas giant, similar to Jupiter, but previously ejected from another star system. On balance, however, scientists reckon the new ice-cold star is more probably a brown dwarf rather than a planet as brown dwarfs are fairly common. If so, then it would make WISE J085510.83-071442.5 one of the least massive brown dwarfs known.
Diagram illustrating the closest star systems to the Sun with dates discovered. 

NASA s Wide-field ...
Diagram illustrating the closest star systems to the Sun with dates discovered. NASA's Wide-field Infrared Survey Explorer, or WISE, found two of the four closest systems: the binary brown dwarf WISE 1049-5319 and the brown dwarf WISE J085510.83-071442.5.
NASA/Penn State University
On the new star’s proximity to our solar system, Michael Werner, project scientist for Spitzer at NASA's Jet Propulsion Laboratory in Pasadena, Calif. said, "It’s remarkable that even after many decades of studying the sky we still don't have a complete inventory of the Sun's nearest neighbors."
Testament to that was an earlier discovery credited to Kevin Luhman. In March 2013, Luhman's analysis of WISE images revealed a pair of much warmer brown dwarfs at a distance of just 6.5 light-years, making that system the third closest to the Sun.
This Universe of ours is getting pretty crowded.
More about WISE telescope, NASA JPL Wise mission, Spitzer Space Telescope, NASA, newly discovered stars
 
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