Coldest Known Brown Dwarf Star Discovered Near Our Sun

brown dwarf WISE
An artist’s conception of the brown dwarf WISE J085510.83-071442.5. The Sun is the bright star directly to the right of the brown dwarf. (Robert Hurt/JPL, Janella Williams/Penn State University)

A Penn State University astronomer, Kevin Luhman, has discovered a brown dwarf star that appears to be the coldest of its kind–as cold as the North Pole–using NASA’s Wide-field Infrared Survey Explorer (WISE) and Spitzer Space Telescopes. The newfound star, named WISE  JO85510.83-071442.5, is only 7.2 light years away, making it the fourth closest system to our sun. The object has a temperature between negative 54 and 9 degrees Fahrenheit. Previous record holders for coldest brown dwarfs were around room temperature.

Despite their name, brown dwarfs can be a number of different colors. Brown dwarfs were first hypothesized in 1963 by American astronomer Shiv Kumar who initially called these bodies “black dwarfs” since they were not very luminous at visible wavelengths and instead appear brightest in the infrared range. However, this term was already taken to refer to cold white dwarfs, so American astronomer Jill Tarter proposed the name “brown dwarf” in 1975 because these objects were thought to contain dust. Brown dwarfs begin their lives as collapsing balls of gas like other stars, but they lack the mass necessary to sustain hydrogen fusion reactions and radiate starlight.

WISE  JO85510.83-071442.5 is estimated to be 3 to 10 times the size of Jupiter, a fact that raises questions about its categorization. Because some definitions of brown dwarfs require objects to be at least ten times the mass of Jupiter, the new star may be demoted in the future, just as Pluto was. However, scientists predict the object is most likely a brown dwarf rather than a gas giant planet since brown dwarfs are known to be fairly common.

Sun's closest neighbors
A diagram illustrating the locations of the star systems that are closest to the Sun. The year when each star was discovered to be a neighbor of the Sun is indicated. The brown dwarf WISE J085510.83-071442.5 is the fourth nearest system to the Sun. (Janella Williams, Penn State University)

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