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March 09, 2016

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Old stars might form second crop of planets, imaging study suggests

March 9, 2016
Courtesy of ESO
and World Science staff


As­tro­no­mers have snapped the sharpest pic­ture ev­er of a dusty disc that has formed around a close pair of old stars.

The disc looks sur­pris­ingly si­m­i­lar to those around young stars—rais­ing the in­tri­guing pos­si­bil­ity that such discs could cre­ate a sec­ond genera­t­ion of plan­ets, re­search­ers say.

A dusty ring around the ag­ing dou­ble star IRAS 08544-4431. (Cred­it: ESO/Dig­i­tized Sky Sur­vey 2. Ac­knowl­edge­ment: Da­vide De Mar­tin )


That pos­si­bil­ity re­mains spec­u­la­tive for now.

Many stars form discs of gas and dust around them when they get old. The ma­ter­ial comes from winds that b­low out­ward from the star dur­ing a late phase of its ev­o­lu­tion called the red gi­ant stage. 

Young stars form rath­er si­m­i­lar discs, but as­tro­no­mers had­n’t been able to com­pare the two types be­fore, be­cause of a lack of close, easily viewa­ble old stars with discs.

That has now changed. A team of as­tro­no­mers led by Mi­chel Hil­len and Hans Van Win­ckel from the In­sti­tute for As­tron­o­my in Leu­ven, Bel­gium, used the Very Large Tel­e­scope In­ter­fer­om­eter at Eu­ro­pe­an South­ern Ob­ser­va­to­ry’s Pa­ra­nal Ob­serv­a­to­ry in Chil­e for the work.

“By com­bin­ing light from sev­eral tele­scopes of the Very Large Tel­e­scope In­ter­fer­om­eter, we ob­tained an im­age of stun­ning sharp­ness,” ex­plained Jacques Klus­ka, team mem­ber from Ex­e­ter Un­ivers­ity in the U.K. “The res­o­lu­tion is so high that, for com­par­i­son, we could de­ter­mine the size and shape of a one euro coin seen from a dis­tance of two thou­sand kilo­me­ters” or 1,200 miles.

Their tar­get was the old dou­ble star known as IRAS 08544-4431, ly­ing about 4,000 light-years from Earth in the south­ern con­stella­t­ion Ve­la (The Sails). A light-year is the dis­tance light trav­els in a year. The dou­ble star con­sists of a red gi­ant star, which ex­pelled the ma­te­ri­al in the sur­round­ing dusty disc, and a younger, more nor­mal star or­bit­ing close to it.

The stellar environment around the double star, shown inset. (Cred­it: ESO/Dig­i­tized Sky Sur­vey 2. Ac­knowl­edge­ment: Da­vide De Mar­tin)


The in­ner edge of the dust ring, seen for the first time in these ob­serva­t­ions, matches the ex­pected start­ing place of the dusty disc, the as­tro­no­mers said: clos­er to the stars, the dust would evap­o­rate in the fierce radia­t­ion from the stars.

“We were al­so sur­prised to find a faint­er glow,” which is probably com­ing from a small disc around the com­pan­ion star, said Mi­chel Hillen, lead au­thor of a re­port on the find­ings. 

“We knew the star was dou­ble, but weren’t ex­pect­ing to see the com­pan­ion di­rect­ly,” he added.

“Our ob­serva­t­ions and mod­el­ing open a new win­dow to study the phys­ics of these discs, as well as stel­lar ev­o­lu­tion in dou­ble stars. For the first time the com­plex in­ter­ac­tions be­tween close bi­na­ry [dou­ble] sys­tems and their dusty en­vi­ron­ments can now be re­solved in space and time,” said Van Winckel.

The find­ings are to ap­pear as a let­ter in the jour­nal As­tron­o­my & As­t­ro­phys­ics.


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Astronomers have snapped the sharpest picture ever of a dusty disc that has formed around a close pair of old stars. The disc looks surprisingly similar to those around young stars—raising the intriguing possibility that such discs could create a second generation of planets, researchers say. That possibility remains speculative for now. Many stars form discs of gas and dust around them when they get old. These come from winds that blow outward from the star during a late phase of its evolution called the red giant stage. Young stars form rather similar discs, but astronomers hadn’t been able to compare the two types before, because of a lack of close, easily viewable old stars with discs. That has now changed. A team of astronomers led by Michel Hillen and Hans Van Winckel from the Institute for Astronomy in Leuven, Belgium, used the Very Large Telescope Interferometer at European Southern Observatory’s Paranal Observatory in Chile for the work. “By combining light from several telescopes of the Very Large Telescope Interferometer, we obtained an image of stunning sharpness,” explained Jacques Kluska, team member from Exeter University in the U.K. “The resolution is so high that, for comparison, we could determine the size and shape of a one euro coin seen from a distance of two thousand kilometers” or 1,200 miles. Their target was the old double star known as IRAS 08544-4431, lying about 4,000 light-years from Earth in the southern constellation Vela (The Sails). A light-year is the distance light travels in a year. The double star consists of a red giant star, which expelled the material in the surrounding dusty disc, and a less-evolved more normal star orbiting close to it. The inner edge of the dust ring, seen for the first time in these observations, matches the expected starting place of the dusty disc, the astronomers said: closer to the stars, the dust would evaporate in the fierce radiation from the stars. “We were also surprised to find a fainter glow,” which is probably coming from a small disc around the companion star, said Michel Hillen, lead author of a report on the findings. “We knew the star was double, but weren’t expecting to see the companion directly,” he added. “Our observations and modeling open a new window to study the physics of these discs, as well as stellar evolution in double stars. For the first time the complex interactions between close binary [double] systems and their dusty environments can now be resolved in space and time,” said Van Winckel. The findings are to appear as a letter in the journal Astronomy & Astrophysics. suggests