34. 蓝脱序星bluestraggler的两种形成过程
Vampiresandcollisionsrejuvenatestars
UsingtheNASA/ESAHubbleSpaceTelescope, astronomershaveuncoveredtwodistinctkindsofrejuvenatedstarsintheglobularclusterMessier 30. Anewstudyshowsthatbothstellarcollisionsandaprocesssometimescalledvampirismarebehindthiscosmicfacelift. ThescientistsalsouncoverevidencethatbothsortsofbluestragglerswereproducedduringacriticaldynamicaleventthatoccurredinMessier 30 afewbillionyearsago.
Starsinglobularclustersaregenerallyextremelyold, withagesof 12-13 billionyears. However, asmallfractionofthemappeartobesignificantlyyoungerthantheaveragepopulationand, becausetheyseemtohavebeenleftbehindbythestarsthatfollowedthenormalpathofstellarevolutionandbecameredgiants, havebeendubbedbluestragglers . Bluestragglersappeartoregressfromoldagebacktoahotterandbrighteryouth, gaininganewleaseonlifeintheprocess. AteamofastronomersusedHubbletostudythebluestragglerstarcontentinMessier 30, whichformed 13 billionyearsagoandwasdiscoveredin 1764 byCharlesMessier. Locatedabout 28 000 light-yearsawayfromEarth, thisglobularclusteraswarmofseveralhundredthousandstarsisabout 90 light-yearsacross.
Althoughbluestragglershavebeenknownsincetheearly 1950s, theirformationprocessisstillanunsolvedpuzzleinastrophysics. Itslikeseeingafewkidsinthegrouppictureofarest-homeforretiredpeople. Itisnaturaltowonderwhytheyarethere, saysFrancescoFerrarofromtheUniversityofBolognainItaly, leadauthorofthestudythatwillbepublishedthisweekinNature . Researchershavebeenstudyingthesestarsformanyyearsandknewthatbluestragglersareindeedold. Theywerethoughttohaveariseninatightbinarysystem . Insuchapair, thelessmassivestaractsasavampire, siphoningfreshhydrogenfromitsmoremassivecompanionstar. Thenewfuelsupplyallowsthesmallerstartoheatup, growingbluerandhotterbehavinglikeastaratanearlierstageinitsevolution.
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