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1、A级—理工类第一部分阅读理解BlackHolesTriggerStarstoSelf-DestructScientistshavelongunderstoodthatsupermassiveblackholesweighingmillionsorbillionsofsunscantearapartstarsthatcometooclose.Theblackhole'sgravitypullsharderonthenearestpartofthestar,animbalancethatpullsthestarapartoveraperiodofmi
2、nutesorhours,onceitgetscloseenough.Scientistssaythisunevenpullingisnottheonlyhazardfacingthestar.Thestrainoftheseunbalancedforcescanalsotriggeranuclearexplosionpowerfulenoughtodestroythestarfromwithin.MatthieuBrassartandJean-PierreLuminetoftheObservatoiredeParisinMeudon,Franc
3、e,carriedoutcomputersimulationsofthefinalmomentsofsuchanunfortunatestar'slife,asitveeredtowardsasupermassiveblackhole.Whenthestargetscloseenough,theunevenforcesflattenitintoapancakeshape.Somepreviousstudieshadsuggestedthisflatteningwouldincreasethedensityandtemperatureinsidet
4、hestarenoughtotriggerintensenuclearreactionsthatwouldtearitapart.Butotherstudieshadsuggestedthatthepicturewouldbecomplicatedbyshockwavesgeneratedduringtheflatteningprocessandthatnonuclearexplosionshouldoccur.Thenewsimulationsinvestigatedtheeffectsofshockwavesindetail,andfound
5、thatevenwhentheireffectsareincluded,theconditionsfavoranuclearexplosion."Therewillbeanexplosionofthestar—itwillbecompletelydestroyed,"Brassartsays.Althoughtheexplosionobliteratesthestar,itsavessomeofthestar'smatterfrombeingdevouredbytheblackhole.Theexplosionispowerfulenoughto
6、hurlmuchofthestar'smatteroutoftheblackhole'sreach,hesays.Thedevouringofstarsbyblackholesmayalreadyhavebeenobserved,althoughatamuchlaterstage.Itisthoughtthatseveralmonthsaftertheeventthatripsthestarapart,itsmatterstartsswirlingintotheholeitself.Itheatsupasitdoesso,releasingult
7、ravioletlightandX-rays.Ifstarsdisruptednearblackholesreallydoexplode,thentheycouldinprincipleallowtheseeventstobedetectedatamuchearlierstage,saysJulesHalpernofColumbiaUniversityinNewYork,US."Itmaymakeitpossibletoseethedisruptionofthatstarimmediatelyifitgetshotenough,"hesays.B
8、rassartagrees."PerhapsitcanbeobservedintheX-raysandgammarays,butit's
