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Hidden stellar companions revealed almost next door

March 11, 2013
Courtesy of Penn State University
and World Science staff

A pair of newly dis­cov­ered stars is the third-clos­est star sys­tem to us, ac­cord­ing to a re­port.

That would make the du­o the near­est star sys­tem dis­cov­ered since 1916—and a pos­si­ble tar­get for both plan­et searches and, per­haps one day, a manned mis­sion.

Artist's con­cep­tion of the new­found stars with the Sun in the back­ground. (Cred­it: Janella Wil­liams, Penn State U.)


The find­ing, to be pub­lished in As­t­ro­phys­i­cal Jour­nal Let­ters, was made by Kev­in Luh­man, a Penn State Uni­vers­ity as­tron­o­mer and a re­search­er in Penn State’s Cen­ter for Exoplan­ets and Hab­it­a­ble Worlds. His paper is also on­line here.

WISE J104915.57-531906 is at the cen­ter of the larg­er im­age, which was tak­en by the WISE sat­el­lite. It ap­peared to be a sin­gle ob­ject, but a sharp­er im­age from Gem­i­ni Ob­serv­a­to­ry re­vealed that it was bi­na­ry star sys­tem. (Cred­it: NA­SA/JPL/Gem­i­ni Ob­serv­a­to­ry/AURA/NSF)


Both stars in the new bi­na­ry sys­tem are “brown dwarfs”—stars too light­weight to be­come hot enough to burn through the nu­clear pro­cess of hy­dro­gen fu­sion, he ex­plained. As a re­sult, they are cool and dim, re­sem­bling a gi­ant plan­et like Ju­pi­ter more than a bright star 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. A light year is the dis­tance light trav­els in a year. 

“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,” he added. It might one day be one of the first des­tina­t­ions for manned ex­pe­di­tions out­side our so­lar sys­tem, he went on.

The star sys­tem is named WISE J104915.57-531906 be­cause it was dis­cov­ered in a map of the sky ob­tained by the NASA-funded Wide-field In­fra­red Sur­vey Ex­plor­er, or WISE, sat­el­lite. It’s only slightly far­ther away than the second-clos­est star, Barnard’s star, which was dis­cov­ered six light years from the Sun in 1916. 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.

“One ma­jor goal when pro­pos­ing WISE was to find the clos­est stars to the Sun,” and this fits the bill, said Ed­ward (Ned) Wright, the prin­ci­pal in­ves­ti­ga­tor for the sat­el­lite and an as­tron­o­mer at the Uni­vers­ity of Cal­i­for­nia Los An­ge­les. 

This di­a­gram il­lus­trates 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. (Cred­it: Janella Wil­liams, Penn State U.)


Luh­man said the new­found star pair is not “Neme­sis,” a hy­po­thet­i­cal dis­tant, dim ob­ject cir­cling the Sun whose ex­ist­ence as­tron­o­mers have long spec­u­lat­ed about. This star sys­tem “is mov­ing across the sky much too fast to be in or­bit around the Sun,” he ex­plained; this rap­id mo­tion is al­so one clue to its proxim­ity.

Af­ter no­tic­ing the fast mo­tion in da­ta from 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 oth­er sky sur­veys. 

“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,” he said.

By com­bin­ing the var­i­ous de­tec­tions, Luh­man was able to meas­ure the dis­tance through par­al­lax, the ap­par­ent shift of a star in the sky due to the Earth’s or­bit around the Sun. He then used the Gem­i­ni South tel­e­scope on Cerro Pachón in Chil­e to ob­tain its light spec­trum, or pre­cise mix of col­ors, and found that the stars had very cool tem­per­a­tures, and were hence brown dwarfs. “A lot of de­tec­tive work” was in­volved, Luh­man said.


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A pair of newly discovered stars is the third-closest star system to us, according to a report. That would make the duo the nearest star system discovered since 1916—and a possible target for both planet searches and, perhaps one day, a manned mission. The finding, to be published in Astrophysical Journal Letters, was made by Kevin Luhman, a Penn State University astronomer 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 lightweight to become hot enough to burn through the nuclear process of hydrogen fusion, he explained. As a result, they are cool and dim, resembling a giant planet like Jupiter more than a bright star 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. A light year is the distance light travels in a year. “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,” he added. It might one day be one of the first destinations for manned expeditions outside our solar system, he went on. The star system is named WISE J104915.57-531906 because it was discovered in a map of the sky obtained by the NASA-funded Wide-field Infrared Survey Explorer, or WISE, satellite. It’s only slightly farther away than the second-closest star, Barnard’s star, which was discovered six light years from the Sun in 1916. 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. “One major goal when proposing WISE was to find the closest stars to the Sun,” and this is its biggest success yet in that area, said Edward (Ned) Wright, the principal investigator for the satellite and an astronomer at the University of California Los Angeles. Luhman said the newfound star pair is not “Nemesis,” a hypothetical distant, dim object circling the Sun whose existence astronomers have long speculated about. This star system “is moving across the sky much too fast to be in orbit around the Sun,” he explained; this rapid motion is also one clue to its proximity. After noticing the fast motion in data from 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 other sky surveys. “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,” he said. By combining the various detections, Luhman was able to measure the distance through parallax, the apparent shift of a star in the sky due to the Earth’s orbit around the Sun. He then used the Gemini South telescope on Cerro Pachón in Chile to obtain its light spectrum, or precise mix of colors, and found that the stars had very cool temperatures, and were hence brown dwarfs. “A lot of detective work” was involved, Luhman said.