Looking Up – Bob Eklund

A pair of newly discovered stars is the third-closest star system to the Sun, according to a paper that will be published in Astrophysical Journal Letters. The duo is the closest star system discovered since 1916. The discovery was made by Kevin Luhman, an associate professor of astronomy and astrophysics at Penn State University and a researcher in Penn State’s Center for Exoplanets and Habitable Worlds.

Both stars in the new binary system are “brown dwarfs”—stars too low in mass to ever become hot enough to ignite hydrogen fusion. As a result, they are very cool and dim, resembling giant planets like Jupiter more than bright stars like the Sun.

“The distance to this brown dwarf pair is 6.5 light years—so close that Earth’s television transmissions from 2006 are now arriving there,” Luhman said. “It will be an excellent hunting ground for planets because it is very close to Earth, which makes it a lot easier to see any planets orbiting either of the brown dwarfs.” Since this is the third-closest star system, in the distant future it might be one of the first destinations for manned expeditions outside our solar system, Luhman noted.

The star system is named “WISE J104915.57-531906” because it was discovered in a map of the entire sky obtained by the NASA-funded Wide-field Infrared Survey Explorer (WISE) satellite. It is only slightly farther away than the second-closest star, Barnard’s star, which was discovered 6.0 light years from the Sun in 1916 by E.E. Barnard. The closest star system consists of Alpha Centauri, found to be a neighbor of the Sun in 1839 at 4.4 light years, and the fainter Proxima Centauri, discovered in 1917 at 4.2 light years.

Edward (Ned) Wright, the principal investigator for the WISE satellite, said “One major goal when proposing WISE was to find the closest stars to the Sun. WISE 1049-5319 is by far the closest star found to date using the WISE data, and the close-up views of this binary system we can get with big telescopes like Gemini and the future James Webb Space Telescope will tell us a lot about the low mass stars known as brown dwarfs.” Wright is the David Saxon Presidential Chair in Physics and a professor of physics and astronomy at UCLA.

Astronomers have long speculated about the possible presence of a distant, dim object orbiting the Sun, which is sometimes called Nemesis. However, Luhman has concluded, “We can rule out that the new brown dwarf system is such an object because it is moving across the sky much too fast to be in orbit around the Sun.”

After noticing its rapid motion in the WISE images, Luhman went hunting for detections of the suspected nearby star in older sky surveys. He found that it indeed was detected in images spanning from 1978 to 1999 from the Digitized Sky Survey, the Two Micron All-Sky Survey, and the Deep Near Infrared Survey of the Southern Sky. “Based on how this star system was moving in the images from the WISE survey, I was able to extrapolate back in time to predict where it should have been located in the older surveys—and sure enough, it was there,” Luhman said.

“It was a lot of detective work,” Luhman added. “There are billions of infrared points of light across the sky, and the mystery is which one—if if any of them—could be a star that is very close to our solar system.”

 

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