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Astronomers find bounty of failed stars

October 12, 2011

One youngster only six times heftier than Jupiter

TORONTO, ON – A Uni­ver­si­ty of Toron­to-led team of astronomers has dis­cov­ered over two dozen new free-float­ing brown dwarfs, includ­ing a light­weight young­ster only about six times hefti­er than Jupiter, that reside in two young star clus­ters. What’s more, one clus­ter con­tains a sur­pris­ing sur­plus of them, har­bour­ing half as many of these astro­nom­i­cal odd­balls as nor­mal stars.

“Our find­ings sug­gest once again that objects not much big­ger than Jupiter could form the same way as stars do. In oth­er words, nature appears to have more than one trick up its sleeve for pro­duc­ing plan­e­tary mass objects,” says Pro­fes­sor Ray Jayaward­hana, Cana­da Research Chair in Obser­va­tion­al Astro­physics at the Uni­ver­si­ty of Toron­to and leader of the inter­na­tion­al team that made the dis­cov­ery.

Brown dwarfs strad­dle the bound­ary between stars and plan­ets. Some­times described as failed stars, they glow bright­ly when young, from the heat of for­ma­tion, but cool down over time and end up with atmos­pheres that exhib­it plan­et-like char­ac­ter­is­tics. Sci­en­tists think that most brown dwarfs may have formed like stars, in iso­la­tion from con­tract­ing gas clouds, but some of the puni­est free-floaters may have formed like plan­ets around a star and lat­er eject­ed.

The find­ings come from obser­va­tions using the Sub­aru Tele­scope in Hawaii and the Very Large Tele­scope (VLT) in Chile dur­ing the Sub­stel­lar Objects in Near­by Young Clus­ters (SONYC) sur­vey. Astronomers took extreme­ly deep images of the NGC 1333 and rho Ophi­uchi star clus­ters with Sub­aru at both opti­cal and infrared wave­lengths. Once they iden­ti­fied can­di­date brown dwarfs from the very red col­ors, the research team con­firmed them with spec­tra tak­en at Sub­aru and the VLT. The team’s find­ings will be report­ed in two upcom­ing papers in the Astro­phys­i­cal Jour­nal and pre­sent­ed this week at a sci­en­tif­ic con­fer­ence in Garch­ing, Ger­many.

The six-Jupiter-mass brown dwarf found in the NGC 1333 clus­ter is one of the least mas­sive free-float­ing objects known. “Its mass is com­pa­ra­ble to those of giant plan­ets, yet it does­n’t cir­cle a star. How it formed is a mys­tery,” said Aleks Scholz of the Dublin Insti­tute of Advanced Stud­ies in Ire­land, lead author of one paper and a for­mer post­doc­tor­al fel­low at the Uni­ver­si­ty of Toron­to. Sev­er­al oth­er new­ly iden­ti­fied brown dwarfs in both NGC 1333 and rho Ophi­uchi clus­ters have mass­es below 20 times that of Jupiter.

“Brown dwarfs seem to be more com­mon in NGC 1333 than in oth­er young star clus­ters. That dif­fer­ence may be hint­ing at how dif­fer­ent envi­ron­men­tal con­di­tions affect their for­ma­tion,” says Uni­ver­si­ty of Toronto’s Koralj­ka Muz­ic, lead author of the sec­ond paper.

 “We could not have made these excit­ing dis­cov­er­ies if not for the remark­able capa­bil­i­ties of Sub­aru and the VLT. Instru­ments that can image large patch­es of the sky and take hun­dreds of spec­tra at once are key to our suc­cess,” said co-author Moto­hide Tamu­ra of the Nation­al Astro­nom­i­cal Obser­va­to­ry of Japan.

Oth­er co-authors of the two papers are Vin­cent Geers of ETH Zurich in Switzer­land, also a for­mer U of T post­doc, and Mar­i­an­gela Bonavi­ta of the Uni­ver­si­ty of Toron­to.

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Ray Jayaward­hana
Depart­ment of Astron­o­my and Astro­physics
Uni­ver­si­ty of Toron­to

Dr. Koralj­ka Muz­ic
Uni­ver­si­ty of Toron­to

Dr. Aleks Scholz
Dublin Insti­tute for Advanced Stud­ies
353 (0)86 126 6608

Dr. Moto­hide Tamu­ra
Nation­al Astro­nom­i­cal Obser­va­to­ry of Japan
+81 (0)90 7198 8360

Sean Bet­tam
Com­mu­ni­ca­tions, Fac­ul­ty of Arts & Sci­ence
Uni­ver­si­ty of Toron­to