(Really) Cool Stars Discovered

August 23, 2011—Astronomers have located some stars that are really cool. Temperature-wise, that is. Scientists using data from NASA’s Wide-field Infrared Survey Explorer (WISE) have discovered the coldest class of star-like bodies, with temperatures as cool as the human body. Astronomers hunted these dark orbs, termed Y dwarfs, for more than a decade without success. When viewed with a visible-light telescope, they are nearly impossible to see. However, WISE’s infrared vision allowed the telescope to finally spot the faint glow of six Y dwarfs relatively close to our sun, within a distance of about 40 light-years. The Y’s are the coldest members of the brown dwarf family. Brown dwarfs are sometimes referred to as “failed” stars. They are too low in mass to fuse atoms at their cores and thus don’t burn with the fires that keep stars like our sun shining steadily for billions of years. Instead, these objects cool and fade with time, until what little light they do emit is at infrared wavelengths. Astronomers study brown dwarfs to better understand how stars form and understand the atmospheres of planets beyond our solar system. The atmospheres of brown dwarfs are similar to those of gas giant planets like Jupiter, but they are easier to observe because they are alone in space, away from the blinding light of a parent star. So far, WISE data have revealed 100 new brown dwarfs, with six being classified as cool Y’s. One of the Y dwarfs, called WISE 1828+2650, is the record holder for the coldest brown dwarf with an estimated atmospheric temperature cooler than room temperature, or less than 80 degrees F. “The brown dwarfs we were turning up before this discovery were more like the temperature of your oven,” said Davy Kirkpatrick, a WISE science team member at the California Institute of Technology. “With the discovery of Y dwarfs, we’ve moved out of the kitchen and into the cooler parts of the house.”

NASA’s Wide-field Infrared Survey Explorer has uncovered the coldest brown dwarf known so far (green dot in very center of this infrared image). Called WISE 1828+2650, this chilly star-like body isn’t even as warm as a human body, at less than about 80 degrees Fahrenheit. Image credit: NASA/JPL-Caltech/UCLA United Launch Alliance’s Delta II rocket lifts off carrying NASA’s WISE satellite toward space on December 14, 2009. Image credit: United Launch Alliance/Bill Hartenstein

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