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Sharpest views of a colossal, violent, star

Aug. 3, 2009
Courtesy ESO
and World Science staff

As­tro­no­mers have cap­tured the sharpest views yet of the “su­per­gi­ant” star Be­tel­geuse. The pic­tures re­veal that the star throws out a vast plume of gas al­most as large as our So­lar Sys­tem and has a gi­gantic bub­ble boil­ing on its sur­face, re­search­ers say.

The findings pro­vide clues to ex­plain how mam­moths such as Be­tel­geuse (pro­nounced BET-el-jooz) shed ma­te­ri­al at such a tre­men­dous rate, ac­cord­ing to astro­nom­ers.

An image of the su­per­gi­ant star Be­tel­geuse ob­tained with ESO’s Very Large Tel­e­scope by as­tron­o­mer Pierre Der­vella and col­leagues. New tech­niques al­lowed the team to ob­tain the sharpest ev­er im­age of Be­tel­geuse, even with Earth’s tur­bu­lent, im­age-distorting at­mos­phere in the way. The res­o­lu­tion is as fi­ne as 37 mil­li­arc­sec­onds, rough­ly the size of a ten­nis ball on the In­ter­na­tion­al Space Sta­tion, as seen from the ground. The im­age is based on da­ta ob­tained in near-infrared light, through dif­fer­ent fil­ters. The field of view is about half an arc­sec­ond wide, North is up, East is left. (Cour­te­sy ESO)


Be­tel­geuse — the sec­ond bright­est star in the con­stella­t­ion of Ori­on, the Hunt­er — is a red su­per­gi­ant, one of the big­gest stars known, and al­most a thou­sand times larg­er than our Sun. It is al­so one of the bright­est stars known, emit­ting more light than 100,000 Suns.

Such ex­treme prop­er­ties fore­tell the de­mise of a short-lived stel­lar king, as­tro­no­mers say. With an age of only a few mil­lion years, Be­tel­geuse is al­ready near­ing the end of its life and is soon doomed to ex­plode as a su­per­no­va. When it does, the su­per­no­va should be easily vis­i­ble from Earth, even in broad day­light.

Red su­per­gi­ants still hold sev­eral un­solved mys­ter­ies. One of them is just how these be­he­moths shed such tre­men­dous quanti­ties of ma­te­ri­al — about the mass of the Sun every 10,000 years.

Two teams of as­tro­no­mers have used the Eu­ro­pe­an South­ern Ob­serv­a­to­ry’s Very Large Tel­e­scope at Cer­ro Pa­ra­nal, Chile, and ad­vanced tech­nolo­gies to ex­am­ine the star. Their com­bined work sug­gests that an­swers may well be at hand, the re­search­ers said.

The first re­search team used tech­niques that al­lowed high enough res­o­lu­tion that a ten­nis ball could be seen on the In­terna­t­ional Space Sta­t­ion. “We have de­tected a large plume of gas ex­tend­ing in­to space from the sur­face of Be­tel­geuse,” said Pierre Ker­vella from the Par­is Ob­serv­a­to­ry, who led the team.

This shows that the star’s outer lay­er “is not shed­ding mat­ter evenly in all di­rec­tions,” added Ker­vella. Two mech­a­nisms could ex­plain this, he said. One as­sumes that the mass loss oc­curs above the po­lar caps of the gi­ant star, pos­sibly be­cause of its rota­t­ion. The oth­er pos­sibil­ity is that such a plume is gen­er­at­ed above large-scale gas mo­tions in­side the star, known as con­vec­tion — si­m­i­lar to the cir­cula­t­ion of wa­ter heat­ed in a pot. 

To ar­rive at a so­lu­tion, as­tro­no­mers needed to probe the be­he­moth in still fin­er de­tail. To do this Kei­ichi Ohnaka from the Max Planck In­sti­tute for Ra­di­o As­tron­o­my in Bonn, Ger­ma­ny, and his col­leagues used in­ter­fer­om­etry, a tech­nique that com­bines light from dif­fer­ent in­stru­ments, in this case three 1.8-metre Aux­il­ia­ry Tel­e­scopes of the Very Large Tel­e­scope. 

The as­tro­no­mers ob­tained ob­serva­t­ions as sharp as those of a gi­ant, vir­tu­al 48-metre tel­e­scope. With such res­o­lu­tion, the as­tro­no­mers were able to de­tect in­di­rectly de­tails four times fin­er still than the pre­vi­ous im­age—in oth­er words, the size of a mar­ble on the International Space Station, as seen from the ground. 

“We de­tected how the gas is mov­ing in dif­fer­ent ar­eas of Be­tel­geuse’s sur­face, the first time this has been done for a star oth­er than the Sun,” said Ohnaka. The ob­serva­t­ions, he added, show that the gas in Be­tel­geuse’s at­mos­phere is mov­ing vig­or­ously up and down, and that these bub­bles are as large as the star it­self. The ob­serva­t­ions have led the as­tro­no­mers to pro­pose that these large-scale gas mo­tions roil­ing un­der Be­tel­geuse’s red sur­face are be­hind the ejec­tion of the mas­sive plume in­to space.


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Astronomers have captured the sharpest ever views of the supergiant star Betelgeuse. The pictures reveal that the star has a vast plume of gas almost as large as our Solar System and a gigantic bubble boiling on its surface, researchers say. These discoveries provide important clues to help explain how mammoths such as Betelgeuse (pronounced BET-el-jooz) shed material at such a tremendous rate. Betelgeuse — the second brightest star in the constellation of Orion, the Hunter — is a red supergiant, one of the biggest stars known, and almost a thousand times larger than our Sun. It is also one of the brightest stars known, emitting more light than 100,000 Suns. Such extreme properties foretell the demise of a short-lived stellar king, astronomers say. With an age of only a few million years, Betelgeuse is already nearing the end of its life and is soon doomed to explode as a supernova. When it does, the supernova should be easily visible from Earth, even in broad daylight. Red supergiants still hold several unsolved mysteries. One of them is just how these behemoths shed such tremendous quantities of material — about the mass of the Sun in about 10 thousand years. Two teams of astronomers have used the European Southern Observatory Very Large Telescope and advanced technologies to examine the star. Their combined work suggests that an answer to the long-open mass-loss question may well be at hand, the researchers said. The first research team used techniques that allowed high enough resolution that a tennis ball could be seen on the International Space Station. “We have detected a large plume of gas extending into space from the surface of Betelgeuse,” said Pierre Kervella from the Paris Observatory, who led the team. This shows that the star’s louter layer “is not shedding matter evenly in all directions,” added Kervella. Two mechanisms could explain this, he said. One assumes that the mass loss occurs above the polar caps of the giant star, possibly because of its rotation. The other possibility is that such a plume is generated above large-scale gas motions inside the star, known as convection — similar to the circulation of water heated in a pot. To arrive at a solution, astronomers needed to probe the behemoth in still finer detail. To do this Keiichi Ohnaka from the Max Planck Institute for Radio Astronomy in Bonn, Germany, and his colleagues used interferometry, a technique that combines light from different instruments, in this case three 1.8-metre Auxiliary Telescopes of the Very Large Telescope. The astronomers obtained observations as sharp as those of a giant, virtual 48-metre telescope. With such resolution, the astronomers were able to detect indirectly details four times finer still than the previous image—in other words, the size of a marble on the ISS, as seen from the ground. “We detected how the gas is moving in different areas of Betelgeuse’s surface ― the first time this has been done for a star other than the Sun,” said Ohnaka. The observations, he added, show that the gas in Betelgeuse’s atmosphere is moving vigorously up and down, and that these bubbles are as large as the star itself. The observations have led the astronomers to propose that these large-scale gas motions roiling under Betelgeuse’s red surface are behind the ejection of the massive plume into space.