Ablackholeisaplaceinspacewheregravitypullssomuchthatevenlightcannotgetout.Thegravityissostrongbecausematterhasbeensqueezedintoatinyspace.Thiscanhappenwhenastarisdying.

Becausenolightcangetoutpeoplecan’tseeblackholes.Spacetelescopeswithspecialtoolscanhelpfindblackholes.Thespecialtoolscanseehowstarsthatareveryclosetoblackholesactdifferentlyfromotherones.

Blackholescanbebigorsmall.Scientiststhinkthesmallestblackholesareassmallasjustoneatom.Theseblackholesareverytinybuthavethemassofalargemountain.Massistheamountofmatteror“staff”inanobject.

Anotherkindofblackholeiscalled“stellar”(星球黑洞).Itsmasscanbeupto20timesmorethanthemassofthesun.TheremaybemanystellarmassblackholesinEarth’sgalaxy.Earth’sgalaxyiscalledtheMilkyWay.

Thelargestblackholesarecalled“supermassive”(超大质量黑洞).Theseblackholeshavemassesthataremorethanonemillionsunstogether.Scientistshavefoundproofthateverylargegalaxycontainsasupermassiveblackholeatitscenter.ThesupermassiveblackholeatthecenteroftheMilkyWaygalaxyhasamassequaltoaboutfourmillionsunsandwouldfitinsideaverylargeballthatcouldholdafewmillionEarths.

Scientiststhinkthesmallestblackholesformedwhentheuniversebegan.Stellarblackholesaremadewhenthecenterofaverybigstarfallsinuponitselforfallsapart.Whenthishappensitexplodedpartofthestarintospace.Scientiststhinksupermassiveblackholesweremadeatthesametimeasthegalaxytheyarein.

Ablackholecannotbeseenbecausestronggravitypullsallofthelightintothemiddleoftheblackhole.Butscientistscanseehowthestronggravityaffectsthestarsandgasaroundtheblackhole.Scientistscanstudystarstofindoutiftheyareflyingaroundororbitingablackhole.

Whenablackholeandastarareclosetogetherhigh-energylightismade.Thiskindoflightcannotbeseenwithhumaneyes.Scientistsusesatellitesandtelescopesinspacetoseethehigh-energylight.

1.Thegravityofablackholemaybecomesostrongthatlightcannotgetoutwhen____________.

A.thestarisgoingtodie

B.specialtoolsareusedonit

C.otherstar