It’s Freezing on the Surface of this Nearby Star-like Object

by Shannon Hall on April 29, 2014

This artist's conception shows the object named WISE J085510.83-071442.5, the coldest known brown dwarf. Image credit: Penn State University/NASA/JPL-Caltech

This artist’s conception shows the object named WISE J085510.83-071442.5, the coldest known brown dwarf. Image credit: Penn State University/NASA/JPL-Caltech

Our stellar neighborhood just got a little busier … and a little colder.

A brown dwarf that’s as frosty as the Earth’s North Pole has been discovered lurking incredibly close to our Solar System. Astronomer Keven Luhman from Pennsylvania State University used NASA’s Wide-field Infrared Survey Explorer (WISE) and the Spitzer Space Telescope to pinpoint the object’s temperature and distance. This is the coldest brown dwarf found so far, and it’s a mere 7.2 light-years away, making it the seventh closest star-like object to the Sun.

“It is very exciting to discover a new neighbor of our Solar System that is so close,” said Luhman in a press release.

Brown dwarfs emerge when clouds of gas and dust collapse. But unlike stars, they never grow dense enough or burn hot enough to ignite nuclear fusion in their cores. They live their lives less massive than stars, but more massive than gas giants. So they burn hot at first, then cool over time. And this newly discovered brown dwarf is as cold as ice. Literally.

WISE surveyed the entire sky twice in its short 14-month lifetime, looking at cooler objects, which radiate in infrared light (but often remain invisible in visible light). It saw cold asteroids, dust clouds, proto-planetary disks, distant galaxies and hundreds of brown dwarfs.

But one of these objects — dubbed WISE J085510.83-071442.5 — was moving rapidly, suggesting it was extremely close to the Solar System. All stars orbit around the Milky Way, with apparent motions seen on the timescale of hundreds of years. Stars close to the Sun, however, can be seen to make the slightest of movements on the timescale of just a few years. This object appeared to move in just a few months.

 This animation shows the coldest brown dwarf yet seen, and the fourth closest system to our sun. Called WISE J085510.83-071442.5, this dim object was discovered through its rapid motion across the sky. It was first seen in two infrared images taken six months apart in 2010 by NASA's Wide-field Infrared Survey Explorer, or WISE (see orange triangles). Two additional images of the object were taken with NASA's Spitzer Space Telescope in 2013 and 2014 (green triangles). All four images were used to measure the distance to the object -- 7.2 light-years -- using the parallax effect. › See animation The Spitzer data were used to show that the body is as cold as the North Pole (or between minus 54 and 9 degrees Fahrenheit, which is minus 48 to minus 13 degrees Celsius). Image credit: NASA/JPL-Caltech/Penn State

Click on the image above to see an animation of WISE J085510.83-071442.5. It was first seen in two infrared images taken six months apart in 2010 by WISE (see orange triangles). Two additional images of the object were taken with NASA’s Spitzer Space Telescope in 2013 and 2014 (green triangles). Image credit: NASA/JPL-Caltech/Penn State

After first spotting this wacky object in the WISE data, Luhman analyzed additional images taken with the Spitzer Space Telescope and the Gemini South Pole Telescope in Chile. The combined detections taken from different positions around the Sun enabled the measurement of the objects parallax — the apparent position of the object against a background set of stars as seen along multiple lines of sight — allowing Luhman to determine the objects distance.

Spitzer’s additional observations helped pin down the objects chilly temperature, which can be determined based on how much light it gives off in different colors. Like a flame, the hottest part is blue, while the coldest part is red. Luhman found the brown dwarfs temperature to be between –54° and 9° Fahrenheit (–48° to –13° Celsius). Previous record-holders for the coldest brown dwarfs were about room temperature.

“It is remarkable that even after many decades of studying the sky, we still do not have a complete inventory of the Sun’s nearest neighbors,” said Michael Werner from NASA’s Jet Propulsion Laboratory. “This exciting new result demonstrates the power of exploring the universe using new tools, such as the infrared eyes of WISE and Spitzer.”

With a stretch of the imagination and advanced technology, it’s possible that other cooler objects, be them brown dwarfs of even rogue exoplanets, are yet closer to the Sun.

The paper will be published in the Astrophysics Journal and is available for download here.

About 

Shannon Hall is a freelance science journalist. She holds two B.A.'s from Whitman College in physics-astronomy and philosophy, and an M.S. in astronomy from the University of Wyoming. Currently, she is working toward a second M.S. from NYU's Science, Health and Environmental Reporting program.

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