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Two giant stars are starting to merge, astronomers say

Dec. 7, 2014
Courtesy of RUVID Valencian Universities Network
and World Science staff

Sci­en­tists are re­port­ing the dis­cov­ery of a pair of huge stars that are cir­cling each oth­er and are start­ing to merge.

The­o­ret­i­cal mod­els pre­dict that the big­gest stars form by merg­ing with oth­er smaller stars, ac­cord­ing to the re­search­ers. These stars in­i­tially make up “bi­na­ry” or “mul­ti­ple” sys­tems, in which two or more stars move around each oth­er about a com­mon cen­tral point.

Artistic rendering of MY Cam system. The proportions between the parts reflect the analysis results. The stars are deformed by their fast rotation and the companion's pull. (Credit: Javier Lorenzo, U. of Alicante).


The new study ex­am­ines what sci­en­tists call the larg­est known sys­tem of bi­na­ry stars that are ex­pected to merge and that are still “main se­quence” stars, mean­ing they’re in their ac­tive, fuel-burning phase. 

The bi­na­ry—known as MY Camel­o­par­dal­is—is al­so “e­clips­ing,” mean­ing that the stars some­times block each oth­er along the line of sight from Earth, say the re­search­ers, who pub­lished their find­ings in the jour­nal As­tron­o­my & As­t­ro­phys­ics.

The scientists, who re­ceived help from am­a­teur sky-watchers, also say the two stars are al­ready touch­ing, weigh the equiv­a­lent of 38 and 32 Suns, re­spec­tive­ly, and take just 1.2 Earth days to cir­cle each oth­er. The stars are al­so be­lieved to be slightly egg-shaped, as each dis­torts the oth­er through its gravita­t­ional pull.

The stars—clas­si­fied as “type O,” mean­ing the bright­est, hot­test, heav­i­est and blu­est type­—are al­so quite young and were al­ready al­most touch­ing when they first formed, ac­cord­ing to the group. And they’re ex­pected to merge be­fore they them­selves change much fur­ther.

Stars which, like the Sun, move alone in their gal­axy are a mi­nor­ity, said the re­search­ers, from the Uni­vers­ity of Al­i­can­te in Spain and oth­er in­sti­tu­tions. Most stars spend their lives tied by gra­vity to one or more com­pan­ion stars. MY Ca­mel­o­par­dalis, in the con­stella­t­ion of the Gi­raffe, is the bright­est star in a clus­ter known as Al­i­can­te 1. Re­search­ers at the uni­vers­ity have iden­ti­fied the group as a small stel­lar nurse­ry, or star-forming re­gion. 

MY Ca­mel­o­par­dalis was known for over half a cen­tu­ry as just a sin­gle, huge star, but only a dec­ade ago rec­og­nized as an eclips­ing bi­na­ry. The eclips­ing prop­er­ty, in which one star blocks our view of the oth­er, al­lows as­tro­no­mers to study the sys­tem in de­tail as the light com­ing from the sys­tem changes in a reg­u­lar way. 

The as­t­ro­phys­i­cists stud­ied this light us­ing an in­stru­ment known as a spec­tro­graph at the Calar Al­to Ob­serv­a­to­ry in Spain. Am­a­teur as­tro­no­mers helped by meas­ur­ing the changes in the amount of light com­ing from the sys­tem.

Among oth­er things, the re­search­ers con­clud­ed that the points on the sur­faces of the stars are mov­ing at over a 10,000 miles (16,000 kilo­me­ters) a sec­ond; that the ma­te­ri­al in their out­er lay­ers is mix­ing; and that the stars are less than two mil­lion years old, so they haven’t had time to evolve since their birth.

While they’re ex­pected to merge, it’s un­clear ex­actly how this will play out. Some the­o­ret­i­cal mod­els sug­gest that the merg­er pro­cess is ex­tremely fast, re­leas­ing a huge amount of en­er­gy in a kind of ex­plo­sion. Oth­er stud­ies fa­vor a less vi­o­lent but still spec­tac­u­lar pro­cess.


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Scientists are reporting the discovery of a pair of huge stars that are circling each other and are starting to merge. Theoretical models predict that the biggest stars form by merging with other smaller stars, according to the researchers. These stars initially make up “binary” or “multiple” systems, in which two or more stars move around each other about a common central point. The new study examines what scientists call the largest known system of binary stars that are expected to merge and that are still “main sequence” stars, meaning they’re in their active, fuel-burning phase. The binary—known as MY Camelopardalis—is also “eclipsing,” meaning that the stars sometimes block each other along the line of sight from Earth, said the researchers, who published their findings in the journal Astronomy & Astrophysics. The researchers, who received help from amateur sky-watchers, say the two stars are already touching, weigh the equivalent of 38 and 32 Suns, respectively, and take just 1.2 Earth days to circle each other. The stars are also believed to be slightly egg-shaped, as each distorts the other through its gravitational pull. The stars—classified as “type O,” meaning the brightest, hottest, heaviest and bluest type—are also quite young and were already almost touching when they first formed, according to the group. And they’re expected to merge before they themselves change much further. Stars which, like the Sun, move alone in the Galaxy by trailing only their planetary system are a minority, said the researchers, from the University of Alicante in Spain and other institutions. Most stars spend their lives tied by gravity to one or more companion stars. MY Camelopardalis, in the constellation of the Giraffe, is the brightest star in a cluster known as Alicante 1. Researchers at the university recently identified the group a small stellar nursery, or star-forming region. MY Camelopardalis was known for over half a century as just a single, huge star, but only a decade ago recognized as an eclipsing binary. The eclipsing property, in which one star blocks our view of the other, allows astronomers to study the system in detail as the light coming from the system changes in a regular way. The astrophysicists studied this light using an instrument known as a spectrograph at the Calar Alto Observatory in Spain. Amateur astronomers helped by measuring the changes in the amount of light coming from the system. Among other things, the researchers concluded that the points on the surfaces of the stars are moving at over a 10,000 miles (16,000 kilometers) a second; that the material in their outer layers is mixing; and that the stars are less than two million years old, so they haven’t had time to evolve since their birth. While they’re expected to merge, it’s unclear exactly how this will play out. Some theoretical models suggest that the merger process is extremely fast, releasing a huge amount of energy in a kind of explosion. Other studies favor a less violent but still spectacular process.