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Astronomers may be learning to predict when a star is about to explode

Dec. 1, 2011
Courtesy of Ohio State University
and World Science staff

New re­search may be help­ing as­tro­no­mers learn what sig­nals will pre­dict a star is about to ex­plode.

Many stars die ex­plo­sively in events called su­pe­r­novas, but sci­en­tists can’t cur­rently pre­dict when a star is about to meet that fate. This means they usu­ally have to learn eve­ry­thing they know about these stars af­ter they have al­ready burst—de­priv­ing re­search­ers of be­fore-and-af­ter da­ta that would help ex­plain the whole pro­cess.

This Large Bin­oc­u­lar Tel­e­scope im­age of the Whirl­pool Gal­axy is part of a sur­vey in which as­tro­no­mers are search­ing for signs that stars are about to go su­per­no­va. The in­sets show one bi­na­ry star sys­tem be­fore (left) and af­ter (right) one of its stars went su­per­no­va. (Cred­it: Im­age by Dorota Szczy­giel, cour­te­sy OSU)


As­tro­no­mers have there­fore been scan­ning 25 near­by ga­lax­ies for stars that bright­en and dim in un­usu­al ways, hop­ing to catch a few that were about to meet an ex­plo­sive end. In the three years since the work be­gan, a dou­ble star sys­tem in the Whirl­pool Gal­axy has been first among the stars they’ve cat­a­logued to yield a super­nova.

The findings from the Ohio State Uni­vers­ity sur­vey, car­ried out us­ing Ari­zon­a’s Large Bin­oc­u­lar Tel­e­scope, are de­tailed in a pa­pe­r sub­mit­ted to The As­t­ro­phys­i­cal Jour­nal.

The as­tro­no­mers were try­ing to find out if there are pat­terns of bright­ening or dim­ming that her­ald the end of a star’s life. In­stead, they saw one star in this bi­na­ry sys­tem dim no­ticeably be­fore the oth­er ex­ploded in a su­pe­r­no­va last sum­mer.

Al­though it was a sur­prise to real­ize you might have to watch one star to pre­dict its part­ner’s death, the as­tro­no­mers say what­ev­er works, they’ll take it. The point “is to look for any kind of sig­na­ture be­hav­ior that will en­a­ble us to iden­ti­fy stars be­fore they ex­plode,” said Ohio State as­tron­o­mer Chris­to­pher Ko­cha­nek.

“Maybe stars give off a clear sig­nal of im­pend­ing doom, may­be they don’t,” added study co-author Krzystof Sta­nek, al­so an as­tron­o­mer at Ohio State. “But we’ll learn some­thing new about dy­ing stars no mat­ter the out­come.”

Dorota Szczy­giel, a post­doc­tor­al re­searcher at the uni­vers­ity who led the study of the su­pe­r­no­va, said “the odds are ex­tremely low that we would just hap­pen to be ob­serv­ing a star for sev­er­al years be­fore it went su­pe­r­no­va. We would have to be ex­tremely lucky.”

With the new sur­vey, “we’re mak­ing our own luck,” she added. “We’re stu­dying all the var­i­a­ble stars in 25 ga­lax­ies, so that when one of them hap­pens go su­pe­r­no­va, we’ve al­ready com­piled da­ta on it.” The su­pe­r­no­va, la­beled 2011dh, was first de­tected on May 31 and is still in a bright­ened state due to the ex­plo­sion. The event took place in the Whirl­pool Gal­axy, al­so known as M51.

A bi­na­ry star sys­tem is a com­mon ar­range­ment in which two stars are or­bit­ing each oth­er. This bi­na­ry sys­tem is thought to have con­tained one very bright blue star and one even brighter red star. From what the as­tro­no­mers can tell, the red star is ap­par­ently the one that dimmed over the three years, be­fore the blue star in­i­ti­at­ed the su­pe­r­no­va. When the re­search­ers re­viewed the Large Bin­oc­u­lar Tel­e­scope da­ta and Hub­ble Spa­ce Tel­e­scope im­ages of M51, they saw that the red star had dimmed by about 10 pe­r­cent over three years, at a pa­ce of three pe­r­cent per year.

Szczy­giel be­lieves the red star likely sur­vived its part­ner’s su­pe­r­no­va. “After the light from the ex­plo­sion fades away, we should be able to see the com­pan­ion that did not ex­plode,” she said.

As as­tro­no­mers gath­er da­ta from more su­pe­r­novas – Ko­cha­nek spec­u­lates that as many as one per year could emerge from their da­ta set – they could as­sem­ble a kind of lit­mus test to pre­dict wheth­er a giv­en star is near death.

The team won’t be watch­ing our sun for any changes, though. Since it’s less than one-tenth the weight of the star in su­pe­r­no­va 2011dh, our star is pre­dicted to meet a fairly bor­ing, non-ex­plo­sive end. “It’ll just fiz­zle out,” Ko­cha­nek said. “But that’s okay – you don’t want to live around an ex­cit­ing star.”


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New research on a double star system may be helping astronomers learn what signals to look for that will show a star is about to explode. Many stars die explosively in events called supernovas, but scientists can’t currently predict when a star is about to meet that fate. This means they usually have to learn everything they know about these stars after they has already burst—depriving them of key before-and-after data that would help reveal how the process plays out. Astronomers have therefore been scanning 25 nearby galaxies for stars that brighten and dim in unusual ways, hoping to catch a few that were about to meet an explosive end. In the three years since the work began, a double star system in the Whirlpool Galaxy has been first among the stars they’ve catalogued to explode, a type of stellar death known as a supernova. Early results from the Ohio State University survey, carried out using Arizona’s Large Binocular Telescope, are detailed in a paper submitted to the Astrophysical Journal. The astronomers were trying to find out if there are patterns of brightening or dimming that herald the end of a star’s life. Instead, they saw one star in this binary system dim noticeably before the other exploded in a supernova last summer. Although it was a surprise to realize you might have to watch one star to predict its partner’s death, the astronomers say whatever works, they’ll take it. The point “is to look for any kind of signature behavior that will enable us to identify stars before they explode,” said Ohio State astronomer Christopher Kochanek. “Maybe stars give off a clear signal of impending doom, maybe they don’t,” added study co-author Krzystof Stanek, also an astronomer at Ohio State. “But we’ll learn something new about dying stars no matter the outcome.” Dorota Szczygiel, a postdoctoral researcher at the university who led the study of the supernova, said “the odds are extremely low that we would just happen to be observing a star for several years before it went supernova. We would have to be extremely lucky.” With the new survey, “we’re making our own luck,” she added. “We’re studying all the variable stars in 25 galaxies, so that when one of them happens go supernova, we’ve already compiled data on it.” The supernova, labeled 2011dh, was first detected on May 31 and is still in a brightened state due to the explosion. The event took place in the Whirlpool Galaxy, also known as M51. A binary star system is a common arrangement in which two stars are orbiting each other. This binary system is thought to have contained one very bright blue star and one even brighter red star. From what the astronomers can tell, the red star is apparently the one that dimmed over the three years, before the blue star initiated the supernova. When the researchers reviewed the Large Binocular Telescope data and Hubble Space Telescope images of M51, they saw that the red star had dimmed by about 10 percent over three years, at a pace of three percent per year. Szczygiel believes the red star likely survived its partner’s supernova. “After the light from the explosion fades away, we should be able to see the companion that did not explode,” she said. As astronomers gather data from more supernovas – Kochanek speculates that as many as one per year could emerge from their data set – they could assemble a kind of litmus test to predict whether a given star is near death. The team won’t be watching our sun for any changes, though. Since it’s less than one-tenth the weight of the star in supernova 2011dh, our star is predicted to meet a fairly boring, non-explosive end. “It’ll just fizzle out,” Kochanek said. “But that’s okay – you don’t want to live around an exciting star.”