Astronomers have discovered the coldest star of its kind — as frosty as Earth’s North Pole — just 7.5 light years away.

Using NASA’s Wide-field Infrared Survey Explorer (WISE) and Spitzer Space Telescopes a Pennsylvania State University astronomer spotted the “brown dwarf” — a dim, star-like body.

Images from the space telescopes pinpointed the object’s distance at 7.2 light-years away, making it the fourth closest system to our Sun.

“It is very exciting to discover a new neighbour of our solar system that is so close,” said Kevin Luhman, an associate professor of astronomy and astrophysics at Penn State.

“In addition, its extreme temperature should tell us a lot about the atmospheres of planets, which often have similarly cold temperatures,” said Luhman.

Brown dwarfs start their lives like stars, as collapsing balls of gas, but they lack the mass to burn nuclear fuel and radiate starlight.

The newfound coldest brown dwarf, named WISE J085510.83—071442.5, has a chilly temperature between minus 48 to minus 13 degrees Celsius.

Previous record holders for coldest brown dwarfs were about room temperature.

Although it is very close to our solar system, WISE J085510.83—071442.5 is not an appealing destination for human space travel in the distant future, researchers said.

“Any planets that might orbit it would be much too cold to support life as we know it,” Luhman said.

“This object appeared to move really fast in the WISE data. That told us it was something special,” said Luhman.

WISE was able to spot the rare object because it surveyed the entire sky twice in infrared light, observing some areas up to three times.

Cool objects like brown dwarfs can be invisible when viewed by visible-light telescopes, but their thermal glow — even if feeble — stands out in infrared light.

Spitzer’s infrared observations helped to determine the frosty temperature of the brown dwarf.

WISE J085510.83—071442.5 is estimated to be 3 to 10 times the mass of Jupiter. With such a low mass, it could be a gas giant similar to Jupiter that was ejected from its star system.

But scientists estimate it is probably a brown dwarf rather than a planet since brown dwarfs are known to be fairly common. If so, it is one of the least massive brown dwarfs known.

(This article was published on April 27, 2014)
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