Evidence(of(the(Existence(of( A(Supermassive(Black(Hole(in(the(Centre(of(the(Milky(Way(Galaxy(! Bhavik!Jayendrakumar!Shah! 1.

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1 Evidence(of(the(Existence(of( A(Supermassive(Black(Hole(in(the(Centre(of(the(Milky(Way(Galaxy( BhavikJayendrakumarShah 1.(Abstract((((( This paper will begin with an introduction to stellar evolution and the Milky Way galaxy. We will then introduceblackholesfromanastrophysicalperspectivetogainatheoreticalunderstandingofwhatexactlytheyare. Following the astrophysical perspective, we will introduce the astronomical perspective by first outlining the observatory instruments that astronomers use to learn about stars, and then describing the main observation methods we have for black holes. Having understood the background of black holes, we shall then focus our discussionontheevidenceofasupermassiveblackholeinthecentreofthemilkywaygalaxy SagittariusA*.We shallfollowachronologicalpatterntoemphasisetheadvancementofourknowledgeaboutsagittariusa*andour Universeatlarge,andtodemonstratethepotentialitholdsforthedevelopmentofourknowledgeinthefuture. 2.(Introduction( a.(stellar(evolution( Thebirthofastaroccursthroughthegravitationalcollapseofagiantmolecularcloudmadeoftwogases hydrogenandhelium combinedwithsomeiceanddust.asthecloudcollapses,thereisareleaseofgravitational potentialenergyintheformofheat,andthepressureinvariousfragmentsofthecloudrises.duetotheincreasein thetemperatureandpressure,thecloud sfragmentscondenseintoarotatingsphereofsuperhotgasknownasa Protostar on the main sequence of the HertsprungKRussell diagram (Exhibit 1). The Protostar undergoes nuclear reactionsasitburnsthehydrogeninitscore(exhibit2),andwhenthisisexhausted,thecoreremainswithhelium whiletheoutershellofthestarcontinuestoburnwithhydrogentoformaredgiant.forstarswithmasslessthan 0.5MSun,theheliumcoredoesnotigniteandthestellarevolutionterminatesearly. Ifthestarhasamassthatisbetween0.5MSunand8MSun,thenthecorebecomessohotthatitalsoignites helium inside it and causes an explosion. The star at this point is at the tip of the Red Giant branch. When the explosionisover,thecoresettlesdownintoconstantburningofhelium,andbythistime,thehydrogenburningin theshellhasended.whentheheliuminthecoreisexhausted,theshellcontinuestoburn,butthecoreconsistsof

2 carbon and oxygen. The star alternates between this hydrogen and helium shell burning, and eventually suffers heavymasslossduetostellarwind,whichremovestheshellofthestaraltogether.thestarcontracts,heatsupand movesrapidlytothefarleftofthehrdiagram.thegasremovedbythestellarwindisionizedbythehotstarandis visible as a planetary nebula. The last hydrogen/helium is used up and the nuclear burningceasesand the star s temperaturedecreases. Stars greater than 8MSun become supernovae. In this form, the carbon core ignites, and nuclear fusion continuestoproduceoxygen,whichitselfignitestoformneon,andsoforth,untilfinallyironforms. Whenastarhasburntoffallitsfuel,thecollapsedstellarremnantstakeoneofthreeformsdependingon themass.whitedwarfs(exhibit3)areformedwhenthemassofthestarislessthan8msun:ifthemassisbetween 0.1MSun and 0.5MSun, then the white dwarf will consist of helium, while if the mass is between 0.5MSun and 8MSun,thenthewhitedwarfwillconsistofcarbonandoxygen.Ifthemassofthestarisgreaterthan8MSun,then thesestarsbecomeeitherneutronstars(exhibit4)orblackholes(exhibit5),basedonthemassoftheircore. b.(milky(way( The Milky Way Galaxy, which is the galaxy in which the Earth and our solar system reside, is one of 200 billiongalaxiesinour(observable)universeandispartofthelocalgroup.themilkywayisapproximately100,000 light years in diameter, and about 1,000 light years thick, forming a diskklike shape. It is estimated to contain between200billionand400billionstars,withpocketsofgasandcloudsofdust.thisgalaxyisabarredspiral,and hasitsbrightestregioninthecentreofit,directedtowardssagittarius.thereasonforthecentreofthemilkyway beingthebrightestisbecauseofthehighestconcentrationofstarsthere.exhibit6andexhibit7showsimagesofthe MilkyWayfromspaceandfromEarth.Noticethebulgeofstarsinthecentre,thedust,andtherotationalfeaturesof thegalaxy.[20] 3.(Astrophysical(Perspective(to(Black(Holes( In physics, an object s gravitational force, g can be calculated as GMm/r2, where G is the gravitational constant,mandmarethemassesofthetwoobjects,andristhedistancebetweenthetwoobjects.ablackholeis anobjectthathasaverylargemassandhencehasaveryhighgravitationalforce strongenoughtonotalloweven

3 lighttoescape.thetheoryofgeneralrelativitysaysthatacompactmasswilldeformspacektimetoformablack hole.aroundtheblackhole,thereisaneventhorizonthattellsusthe pointofnoreturn.itiscalled black because itabsorbsallthelightthathitsitssurfaceandactsjustlikeaperfectblackbodyinthermodynamics. In order to understand black holes from an astrophysical perspective, it is important to understand them fromasimplemathematicalperspectivefirst.inmathematicalterms,ablackholeisasingularitypoint anobject withnodimensionsandallitsmassconcentratedatasinglepointatthecentre(spacektimesingularity).suchan objecthasmass,chargeandangularmomentum, andcanhencebeillustratedas in Exhibit 5. One distinguishing featurebetweenthedefinitionofamathematicalblackholeandaphysicalblackholeisinthedistributionofthe mass and charge within the black hole s event horizon K while a mathematical definition says that the mass and chargeareatasingularitypoint,thephysicaldefinitionsaysthatthemassandchargeisintheeventhorizonandits distributionwithinitisnotimportant. Extendingtheunderstandingofaphysicalblackhole,anastrophysicalblackholeisonethatcanbeformed bythenaturalprocessesoccurringinouruniverse,andisyoungerthantheageoftheuniverseitself.exhibit8shows theprocessofformationofanastrophysicalblackholethroughgravitationalcollapse,asdescribedpreviously.ithas indeedbeenprovenmathematicallyandscientificallythatastrophysicalblackholescanexistinthephysicaluniverse Ktheyhavebeenfoundinsomegalacticbinarysystems,atthecentreofmostgalaxiesandasthesourcesofsome gammaraybursts.[1] 4.(Astronomical(Perspective(to(Black(Holes( a.(stellar(observatory(instruments( Learningaboutthestellarevolutionandstellarremnantsrequireshighlysophisticatedandtechnologically advancedmethodsofobservation.thesemethodsshouldcollectivelycovertheentireelectromagneticspectrumin order to (fully) understand the activities occurring in stars and their remnants. Historically, the four satellites of NASA sgreatobservatoriesprogramhavebeenthemaininstrumentsusedtocollectinformationfromdistantstars. Theseinstrumentsarethefollowing: i. HubbleSpaceTelescope ThisinstrumentcapturesnearKinfrared,visibleandnearKultravioletwavelengthsof

4 the electromagnetic spectrum. It has extended our knowledge of stellar births, deaths, and galaxy evolutions.inparticular,ithasenabledustodiscoverblackholes.[2] ii. ComptonGammaRayObservatory ThisinstrumentcapturedgammaraysandhardXKrays.Itprovidedus withinformationaboutsomeofthemostviolentprocessesintheuniverse.however,itwasdeorbitedin 2000afterfailureoftheobservatory sgyroscope.[3] iii. ChandraXKRayObservatory ThisinstrumentobservessoftXKrays.Ithasgivenusdetailedinformationabout blackholesandquasars,amongotherxkrayprocesses.[4] iv. Spitzer Space Telescope This instrument covers the thermal infrared region of the electromagnetic spectrum.therefore,ithasprovidedusinformationofstarsbydetectingtheinfraredenergyfromthem.[5] SomeofthesuccessorsofthefourGreatObservatorieshavealsocontributedtostellarastronomy.Theyare: thejameswebbspacetelescope(jwst),fermigammakrayspacetelescope,highenergytransientexplorer(hetek 2),SwiftGammaKrayBurstMission,InternationalGammaRayAstrophysicsLaboratory(INTEGRAL),HerschelSpace Observatory,StratosphericObservatoryforInfraredAstronomy(SOFIA),andConstellationKX.[6] b.(observation(methods(for(black(holes( Duetothefactthatblackholesdonotallowlighttoescapethem,theyarenotdirectlyobservable.Theonly (theoretical) radiation that black holes are known to generate is Hawking radiation, which is at a negligible temperature of 10 K14 K. Astronomers and astrophysicists therefore rely on indirect observations to deduce the possibilityoftheexistenceofblackholes.exhibit9showssomeofthefeaturesofablackholethatareusedforsuch indirectobservations.belowarethemethodsexplained: i. Accretion of Matter K The black hole s accretion disk is a diskklike structure that is created due to the conservationofmomentum.thediskismadeofnothingbuttheverysamematterthatgoesintoablack hole. As the matter goes into the black hole, it heats up due to friction and the angular momentum increases.thisincreaseinangularmomentumcausestheblackholetoejectsomeofitintheformofjets, makingspacefornewmattertogointotheblackhole.duetothehightemperature,thesejetshavexkray radiation,makingthempossibletobedetected.[7]

5 ii. XKrayBinaries Theserefertostarsystemsthatarebinary(withtwostarsrotatingaroundeachother).Such starsystemsemitxkrayradiationifoneofthestars(whichmaybeablackhole)isaccretingmatterfromthe other(whichisanormalstar).byknowingtheorbitalparameterssuchastheperiodoftherotationofboth theobjectsandthedistancebetweenthem,wecancalculatethemassofthestarsanddeduceifoneof themisablackhole.[7] iii. QuiescenceandAdvectionKDominatedAccretionFlow Thisoccurswhenthehighenergiesthatarecreated byfrictionarenotradiatedawayintheformofjetsbutinsteadsweptalongwiththeflowenteringamode called an advectionkdominatedaccretionflow.thisistheprocessthatisthoughttobecreating an event horizonaroundtheblackhole.[8][19] iv. QuasiKPeriodicOscillations Theseareoscillationscausedbymattermovingaroundtheinnermoststable orbitoftheblackholeandgeneratingxkrays.theirfrequencies,whicharelinkedtotheirrotationalspeeds, canhelpinfindingoutthemassoftheunderlyingstarandhencededucingifitisablackhole.[8] v. GalacticNuclei Somegalaxiesarethoughttobehavingsupermassiveblackholes(oftheorderofmillions tobillionoftimesthemassofoursun)attheircentre,whichareemittingincredibleradiationsfromthem, rangingfromgammaraystoradiowaves.thesegalaxiesandtheirblackholeseemtohavebeengenerated inarelation,provenbythecorrelationbetweenthemassoftheblackholeandthevelocitydispersionofthe galaxy scentralbulge.[9] vi. GravitationalLensing Thisisaneffectsimilartothatofanopticlens,wherebylightisdeflectedasalens crossesoverit.thedeformationofspacektimearoundablackholewillgeneratethesameeffect.however, thishasnotbeendirectlyobservedforablackholeyet.[10] 5.(Sagittarius(A*(K(A(Supermassive(Black(Hole(in(the(Centre(of(the(Milky(Way( a.(brief(history(of(black(holes( The history of our discovery and understanding of black holes is short. It was as late as 1687 that Isaac Newtondiscoveredtheideaofgravitywhenanapplefelloffatree(onhishead).Atthattime,littlewasknown aboutouruniverse,andtheideaofblackholeswastotallyunheardof. Itwasalmostacenturylaterin1783whenJohnMichellproposed thattheremightbeaheavenlyobject

6 largeenoughtohaveanescapevelocitythatmaybegreaterthanthespeedoflight: Ifthereshouldreallyexistinnatureany[such]bodies,...wecouldhavenoinformationfromsight;yet,if anyotherluminousbodiesshouldhappentorevolveaboutthemwemightstillperhapsfromthemotionsofthese revolvingbodiesinfertheexistenceofthecentraloneswithsomedegreeofprobability,asthismightaffordaclueto some of the apparent irregularities of the revolving bodies, which would not be easily explicable on any other hypothesis. [11] Thistheoreticalideawasdevelopedfurtherbymanygreatminds,includingAlbertEinsteinwiththeTheory ofgeneralrelativity,whichpredictedspacektimecurvaturein1915. b.(discovery(of(a(radio(wave(source(in(the(centre(of(the(milky(way(in(the(1930s( Itwasinthe1930swhenKarlJansky,aradioengineeratBellLabs,wasinvestigatingsourcesofstaticthat interfered with radio voice transmissionson Earth.Usingalargeradiowavesdetectorthatwasadirectionaland rotatableantenna,hecarriedoutexperimentsforoverayearbeforegainingsomecleardataandmeasurements.he noticedthreedifferenttypesofstatic staticfromnearbythunderstorms,staticfromdistantthunderstormsanda hissingsoundfromanunknownsource.overtime,janskyrealisedthatthissourceofradiowasalwayslyingina planefixedinspace.jenskyhadinturndiscoveredthecentreofthemilkywaygalaxy.by1935janskywasableshow "radiations are received any time the antenna is directed towards the Milky Way system, the greatest response beingobtainedwhentheantennapointstowardsthecenterofthesystem."itwasaspotintheconstellationof Sagittariusinthedirectionofthecentreofthegalaxy.[12] c.(mapping(of(the(milky(way(in(the(1960s( Threedecadeslater,in the 1960s, Eric Becklin resumed research onjansky sunusualfinding.becklinhad donesimilarworkonandromeda,ofwhichhefoundthecentrebyseeingwheretheintensityoflightreceivedfrom variouspartsofthegalaxywasatitspeak.thiswaseasiertodoforandromedathanthemilkywaybecausewecan seetheentiregalaxyfromearth,whilewecannotseetheentiremilkywayasweareinsideit.becklinseekedhelpof amilitarycontractortoprepareadevicethatreadsinfraredlight,whichhasalongerwavelengththanvisiblelight, butstilljustsmallenoughtopassthroughthegasanddustparticlesinthemilkyway.usingthis,becklinmanagedto getaclearerviewofthemilkyway,andthisenabledhimtoaccuratelymapthegalaxyandfindthecentreofit.

7 d.(discovery(of(sagittarius(a*(in(the(1970s( SagittariusA*wasdiscoveredinFebruary1974byAmericanastronomersBruceBalickandRobertBrown. TheyusedthebaselineinterferometeroftheNationalRadioAstronomyObservatory(NRAO)tofindactivegalactic nuclei(agn)intherelativelyquietcentreofthemilkyway.thisdiscoverycamejusttwoyearsafterthediscoveryof thefirststrongcandidateforablackhole,cygnusxk1kablackholediscoveredthroughxkraybinariesbyagroupof threeastronomers:charlesthomasbolton,louisewebsterandpaulmurdin.atthesametimeasthediscoveryof SagittariusA*,theBritishastronomerSirMartinReeswasproposingtheexistenceofsupermassiveblackholesinthe centresofmostgalaxies.[18] e.(practical(observation(of(sagittarius(a*(in(the(1990s( In the 1990s, two groups of astronomers attempted to conduct further studies on the radio waves that Janskyhadfound,andBalickandBrownhaddiscoveredtobeSagittariusA*.Onegroup,withEricBecklinandother colleagues,usedthenewkecktelescopeatthemaunakeovolcanoinhawaai.anothergroup,withreinhardgenzel at the Max Planck Institute for ExtraKterrestrial Physics in Germany used the New Technology Telescope in the Chileanmountains.Boththesegroupshadthesameobjective topinpointthepreciselocationofsagittariusa*and findoutwhatexactlyitis.sincesagittariusa*is26,000lightyearsawayfromus,itisextremelydifficulttoobserve it.therefore,thegroupslearntaboutitbytrackingtheorbitsofstarsaroundit.oneproblemthattheastronomers facedwasthatofblurryimagesduetotheearth satmosphereandtemperaturechanges.tosolvethisproblemin the1990s,theytookthousandsofimagesoverashortperiodoftimeandusedtheseimagestoaverageoutthe positionsofeachstar.thisprocessiscalledspeckleimaging.usingthefirstfewyears data,bothgroupsmanagedto calculate the speed of the stars orbiting in the centre of the Milky Way, and their paths. This allowed them to pinpointthepositionofsagittariusa*,anditsgravitationalforce.totheirsurprise,theyfoundoutthatthemassof SagittariusA*wasmillionsofsolarmasses.Suchhighmassesofstarsmeanthattheyareblackholes,soSagittarius A*wasalreadyprovingtobeone.However,duetothefardistanceofit,therewasstillquestionwhetherSagittarius A* was a single object (a black hole) or just a dense cluster of stars in the centre of the Milky Way, pulling the neighbouringstarsclosertothecluster.in2002,thegermanandamericanastronomersnoticedastarsok2that wentreallyclosetosagittariusa*,thesuspectedblackhole.assok2cameclosetotheblackhole,itsorbitingspeed increaseddramatically,buttherewasnowobbledetected.thisprovedthatsagittariusa*wasnotaclusterofstars

8 butasinglestar,andindeed,ablackhole. f.(new(generation(of(astronomical(observation(in(the(21 st (Century( Inearly2000s,newupgradestovarioustelescopesaroundtheworldweremade.Thenewmirrorsinstalled onthetelescopeswerethinner,anddesignedtobemountedonmetalscaffolding.behindthemirrors,pistonsand mortarswerefittedbyengineerstochangethesurfaceofthemirrorastemperaturechangesaffectitsshape,oras atmospheric turbulence blurs the incoming light. Some telescopes had added laser guidekstar adaptive optics (LGSAO), which were projected into the sky. By marking the turbulence of the light coming from these lasers, astronomerswereabletomeasureturbulenceoflightcomingfromthestars,andhencesubtractittogetthenet effect.exhibit10showstheimprovementofimagingofsagittariusanditssurroundingsusingthisadvancedmethod. Anothersimilarmethodwasadaptiveoptics(AO). In 2001, the newly launched Chandra XKrayObservatorywaspointedtowardsSagittariusA*.Atthatvery pointintime,itwitnessedanoutburstofsagittariusaastheblackholeerupted.duetothis,astronomyteamson groundbeganfocusingonitusingthechandraforlongerperiods.theynoticedthatthereareregularflaresthat occuraroundsagittariusa*whenmatterbuildsupneartheeventhorizonbeforefallingintoit.[13][14][15][16] Exhibit11showsSagittariusA*throughtheChandraXKrayObservatory.Noticethedenseclusterofbright starsandthegasesinthesurroundingareas. Exhibit12showsSagittariusA*andtwolightechoes.Noticethebrightflaresthatoccurandmoveawayfrom theblackholeovertime. Exhibit13showstheinferredorbitsofsixstarsaroundSagittariusA*.NoticethatSOK2,beingthenearest star to Sagittarius A* at a distance of m, has the shortest period of 15.2 years and hence has been monitoredorbitingtheblackholeforonecompleterotation.alsocomparetheorbitsofthese6starstotheorbitsof planetsandmoonsinourownsolarsystem.thesestellarorbitsaremuchlargerthantheorbitsinoursolarsystem. i. The(Americans(at(the(Keck(Telescope,(Hawaai( EricBecklin steam,whichincludedandreaghez,conductedadiffractionklimitedimagingstudyofthecentral stellarclusterofthemilkywayusingthewmkeck10mtelescope.theytookanunbiasedsampleof90starsto studytheirhighproperkmotioninthevicinityofsagittariusa*.theyperformedastrometricmeasurementsfor12

9 yearsandradialvelocityspectroscopicmeasurementsfor17years.byfittingthemotiontokeplerianorbits,they initially measured that Sagittarius A* was a star with 2.6 millionsolar massesand a radius of 0.02lightKyears. However,after observing a fully unconstrained orbit for the shortkperiodstarsok2, and by using more advanced telescopeswithlgsao,theywereabletoplacebetterconstraintsonthemassandsizeoftheobjectcausingthe orbitalmotionofstarsinthesagittariusa*region.theyfoundoutthatsagittariusa* smassisabout4.1million solarmassescontainedwithinaradiusoflessthan0.002lightkyears.itsdistanceisabout8000parsecsfromsok2. Furthermore,theyalsocalculatedthatifweweretoassumethatSagittariusA*isablackholeatrestwithrespectto the Milky Way galaxy, then its mass is about 4.5 million solar masses and its distance from SOK2 is about 8400 parsecs.[13][14][22] ii. The(Germans(at(the(New(Technology(Telescope,(Chile( Reinhard Genzel s team used highkresolution nearkinfrared techniques to monitor stellar orbits around SagittariusA*for16years.TheycontributedtothestudyofSagittariusA*anditsstellarorbitsbygreatlyimproving the definition of the coordinate system. By using nearkinfra red (NIR) interferometry in the KKband (2.2 μm wavelength)andadaptiveoptics (AO), they determined the orbits of 28 stars, including the star SOK2,whichhad completeditsperiodaroundtheblackhole(exhibit14).theyrevealedthatallthestellarorbitsaroundtheblackhole werefittingbrilliantwiththesinglekpointkmassidea,hencemakingtheirmeasurementseasiertoobtain.according to the German team, the mass of Sagittarius A* is 4.31 million solar masses and the distance from SOK2 is 8300 parsecs.[15][16][21] g.(further(understanding(of(sagittarius(a*(and(the(milky(way( Bothgroupsofastronomersproducedresultsthatsupporttheevidenceoftheexistenceofasupermassive blackholeinthecentreofourmilkyway.furtherresearchonsagittariusa*tellsusthatitsradioemissionsarenot centred on the hole but instead, arise from a region close to the event horizon. This tells us that the black hole possibly has an accretion disk or a relativistic jet, which is releasing the radio waves. If the location of the radio sourceofsagittariusa*wasexactlyinthecentreoftheblackhole,itwouldhavebeenpossibletoseeitmagnified viagravitationallensing.however,thisisnotthecase.[17] Recently,ateamofastronomersdiscoveredanintermediateKmassblackholein2004.Thisblackhole,GCIRS

10 13E,isorbitingthreelightKyearsfromSagittariusA*andhasamassof1300solarmasses.Thisobservationmayadd supporttotheideathatsupermassiveblackholesgrowbyabsorbingnearbysmallerblackholesandstars. WhilethemeasuredsizeandmassofSagittariusA*canproposealternativemassconfigurations,theywould have collapsed into one single supermassive black hole within a time less than the life of the Milky Way galaxy. Though the Milky Way may contain a supermassive black hole, there is an implication that our galaxy is not of Seyforttype(oneswithblackholesthataretensofmillionstobillionsoftimesthemassofthesunandhavespectral lineemissionsfromhighlyionizedgases).milkyway sradioandiremissionsareoflowintensityincomparison. 6.(Conclusion ( TheempiricalobservationsofSagittariusA*anditsneighbouringstarsprovidesufficientevidencetosaythat themilkywaygalaxyhasasupermassiveblackholeatcentreofit.themainpointsthatsupportthispropositionare: i. The period of SOK2, a star that orbits Sagittarius A* has a period of 15.2 year and its closest distance to SagittariusA*is m.[21][22] ii. FromtheperiodanddistanceofSOK2,wecandeducethemassofSagittarius(usingKeplerianorbits),which turnsouttobeabout4.1millionsolarmasses. iii. TheradiusofSagittariusA*mustbesignificantlylessthan17lighthours,becauseotherwise,SOK2would eithercollidewithitorberippedapartbytidalforces.ithasrecentlybeenproventobenomorethan6.25 lighthours. TheobservationsofasupermassiveblackholeinthecentreofourMilkyWay,SagittariusA*,arecomingata time when astronomers are convinced that giant black holes occupy the centres of nearly all galaxies. Recent researchhasproventhatlargergalaxieshavelargerblackholesattheircentres,suggestingthatthetwomusthave evolvedhandinhand.infactthereisaclearrelationshipbetweenthesizeofasupermassiveblackholeandthesize ofthegalacticbulgethatsurroundsit. AstronomersarenowhopingtogetacloserlookatSagittariusA*andits surroundingfeatures.however,thiswouldrequiretelescopesofmuchlargersizeandefficiency.radioastronomers believethatonewayofdoingsowouldbebylinkingthetelescopesaroundtheworldtoformonelargeearthksized telescope.thefutureofstellarexploration,andastronomy,islookingbrighterthaneverbefore.

11 7.(References [1]ShuangKNanZhang,AstrophysicalBlackHolesinthePhysicalUniverse,Pages3,4,28and29 [2]TheHubbleSpaceTelescope,NationalAeronauticsandSpaceAdministration [3]CGRO,NASAScienceMissionsKhttp://science.nasa.gov/missions/cgro/ [4]ChandraXKrayObservatory,NASA sheasarcobservatories [5]SpitzerKStudyingtheUniverseinInfrared,NASAKhttp:// [6]FeaturedMissions,NASAKhttp:// [7]JeffreyE.McClintockandRonaldA.Remillard,BlackHoleBinaries,Pages2,9,10,11and12K [8]GoddardSpaceFlightCentre,NASAScientistsIdentifySmallestKnownBlackHole [9] LS Sparke and JS Gallagher (2000), Galaxies in the Universe: An Introduction, Pages 17 to 57 K Cambridge UniversityPress.Ch.9.1.ISBN0K521K59704K4 [10]VBozza(2010),GravitationalLensingbyBlackHoles,Page1Khttp://arxiv.org/pdf/ v2 [11] J Michell (1784), Phil. Trans. R. Soc. (London), Page 35 K access/s pdf [12]KGJansky(1933),ElectricalDisturbancesApparentlyofExtraterrestrialOrigin [13]AMGhez,EEBecklinetal(2008),MeasuringDistanceandPropertiesoftheMilkyWay scentralsupermassive BlackHolewithStellarOrbits,Pages1044to [14]AMGhez,EEBecklinetal(1998),HighProperKMotionStarsintheVicinityofSagittariusA*:Evidencefora Supermassive Black Hole at the Center of our Galaxy, Pages 678 to 680 K 637X/509/2/678/pdf/0004K637X_509_2_678.pdf [15]RGenzeletal(2009),MonitoringStellarOrbitsAroundtheMassiveBlackHoleintheGalacticCenter,Pges1075

12 to1080khttp://iopscience.iop.org/0004k637x/692/2/1075/pdf/apj_692_2_1075.pdf [16] R Genzel et al (2003), A Geometric Determination of the Distance to the Galactic Center, L121 to L124 K [17] S S Doeleman et al (2008), EventKhorizonKscale structure in the supermassive black hole candidate at the GalacticCentre,Page78to80Khttp:// [18]DCBackerandRASramek(1999),ProperMotionoftheCompact,NonthermalRadioSourceintheGalactic Center,SagittariusA*,Page805,806and814 [19]RNarayanandJEMcClintock(2008),AdvectionKDominatedAccretionandtheBlackHoleEventHorizon,Pages 733,742to748 [20]RSchodel,DMerrittandAEckart(2009),TheNuclearStarClusteroftheMilkyWay:ProperMotionsandMass, Page1 [21]RGenzeletal(2002),ClosestStarSeenOrbitingtheSupermassiveBlackHoleattheCentreiftheMilkyWay, Pages2to5Khttp://arxiv.org/pdf/astroKph/ v1 [22]EEBecklinetal(2003),TheFirstMeasurementofSpectralLinesinaShortKPeriodStarBoundtotheGalaxy s CentralBlackHole:AParadoxofYouth,L127toL130Khttp://arxiv.org/pdf/astroKph/ v2

13 Exhibit1 Hertzsprung3RussellDiagram ImageSource:EuropeanSouthernObservatory7

14 Exhibit'2' 'Gas'Shells'in'a'Star' ImageSource:PortlandCommunityCollege5

15 ' Exhibit'3' 'White'Dwarf' Source:TheCentreforScienceandEducationattheUCBerkeleySpaceSciences Laboratory<

16 ' Exhibit'4' 'Neutron'Star' Source:

17 ' Exhibit'5' 'Black'Hole' Source:OliverShawGraphicDesignandPrint9http://o9 shawfmp.blogspot.com/2010/04/black9holes.html

18 Exhibit'6' 'Milky'Way'from'Space' Source:

19 Exhibit'7' 'Milky'Way'from'Earth' Source:HighPerformancePhotoGallery6http://universe6beauty.com/Space6photos/Hubble/The6Milky6Way6at650006Meters610227p.html

20 Exhibit'8' 'Astrophysical'Formation'of'a'Black'Hole'Space' Source:Shuang-NanZhang,AstrophysicalBlackHolesinthePhysicalUniverse,Page4 %

21 Exhibit'9' 'Black'Hole'Observational'Features' Source:RoenKelly,Astronomy3http://

22 Exhibit'10' 'Laser'Guide3Star'Adaptive'Optics' Fig. 1. Comparison of raw images obtained with LGSAO and speckle imaging with the Keck 10 m telescopes. The large-scale image is an LGSAO image obtained in The inset LGSAO image (top right) and speckle image (bottom right), also obtained in 2005, are centered on the black hole, Sgr A (marked with a cross), with a field of view of 1:0 00 ; 1:0 00.Theimagequality,depth,andastrometricprecisionhaveallbeengreatlyimprovedwiththeadventofLGSAO. Source:AMGhez,EEBecklinetal(2008),MeasuringDistanceandPropertiesoftheMilkyWay scentralsupermassiveblackholewithstellarorbitsm

23 Exhibit'11' 'Chandra'X0ray'Image'of'Sagittarius'A*' ' Source:ImageoftheDay,NASA5http://

24 Exhibit'12' 'Sagittarius'A*'and'Two'Light'Echoes' ' Source:Wikipedia/

25 Exhibit'13' 'Inferred'Orbits'of'6'Stars'Around' Sagittarius'A*' ' Source:Wikipedia/

26 Exhibit'14' 'S,Star'Cluster'through'Adaptive'Optics' S95 1" 0 1" S96 S14 S93 S54 S92 S80 S97 S63 S23 S57 S81 S91 S56 S90 S82 S94 S48 S53 S27 S26 S28 S29 S37 S36 S12 S5 S52 S39 S47 S40 S64 S59 S6 S60 S4 S31 S2/S13 S49 S20 S35 S7 S79 S8 S77 S67 S34 S46 S78 S68 S22 S11 S76 S1 S44 S69 S25 S9 S10 S45 S24 S75 S74 S32 S58 S70 S19 S18 S21 S66 S73 S101 S102 S103 S104 S51 S61 S43 S33 S30 S50 S42/S41 S71 S72 S65 S55 S87 S112 S85 S99 S98 S100 S105 S62 S83 S38 S86 S17/SgrA*(?) S84 S89 S88 S106 S108 S111 S109 S110 S107 1" 0" 1" Image Source: R Genzel et al (2009), Monitoring Stellar Orbits Around the Massive Black HoleintheGalacticCenter Fig. 1. Finding chart of the S-star cluster. This figure is based on a natural guide star adaptive optics image obtained as part of this study, using NACO at UT4 (Yepun) of the VLT on July 20, 2007 intheh-band. TheoriginalimagewithaFWHMof 75 mas was deconvolved with the Lucy-Richardson algorithm and beam restored with a Gaussian beam with FWHM= 2pix=26.5mas. Stars as faint as m H =19.2 (correspondingroughlytom K =17.7) are detected at the 5σ level. Only stars that are unambiguously identified in several images have designated names, ranging from S1 to S112. Blue labels indicate early-type stars, red labels late-type stars. Stars with unknown spectral type are labelled in black. At the position of Sgr A* some light is seen, which could be either due to Sgr A* itself or due to a faint, so far unrecognized star being confused with Sgr A*.