phys 420: astrophysics & cosmology - home | …€¦ · · 2017-04-28redshift tells you how...

PHYS420:Astrophysics&Cosmology

Dr RichardH.CyburtAssistantProfessorofPhysics

Myoffice:402cintheScienceBuilding

Myphone:(304)384-6006

Myemail:[email protected]

Mywebpage:www.concord.edu/rcyburt

Inpersonoremailisthebestwaytogetaholdofme.

MyOfficeHoursTR5:30-17:00amW4:00-6:00pm

Meetingsmayalsobearrangedatothertimes,byappointment

JointSpringMeetingoftheAppalachianandChesapeakeSectionsoftheAAPTSaturday,April22atConcordUniversity($15/students/guests,$25/AAPT)

§ 8:00– 8:45RegistrationandContinentalBreakfast§ 8:45– 11:45ContributedTalksandDemosI§ 11:45– 12:45Lunch§ 12:45– 1:30PosterSession§ 1:30– 2:30Invitedlecture§ 2:30– 3:15ContributedTalksandDemosII§ 3:15– 4:15Invitedworkshop§ 4:15– 5:00CSAAPTBusinessMeeting(allarewelcome)

Invitedlecture:AstrophysicalHoyleStateEnhancement,Dr.RichardH.Cyburt,ConcordUniversity

InvitedWorkshop:WomenandMinoritiesintheHistoryofPhysics,RoleModelsforToday,Dr.GregoryGood,TheSpencerWeart Director,CenterforHistoryofPhysicsAmericanInstituteofPhysics

DouglasAdamsHitchhiker’sGuidetotheGalaxy

6

OverviewofourGalaxy….Sofar… Dark Halo

Halo

Thick Disk and Metal-Weak Thick Disk

Thin Disk

Bulge

chemicalevolutionZentrum

fuer

Astron

omieun

dAstrop

hysik

,TUBe

rlin

Wearemadeofstardust!Þ Oldstarscontainfewerelements(e.g.iron)thanyoungerstars

Alltheatoms(exceptH,He&Li)werecreatedinstars!PopIII:zero-metallicitystarsPopII:oldhalostarsPopI:youngdiskstars

Alongtimeago...

today

Cosmictime(nottoscale)

BigBang

Larson&Bromm2001

2nd andlatergenerationsofstars(<1M¤)

Firststars(100M¤)

firstgalaxies today’sgalaxies

Newton’sStaticUniverseUniverseisstaticandcomposedofaninfinitenumberofstarsthatarescatteredrandomlythroughoutaninfinitespace.Universeisinfinitelyoldandwillexistforeverwithoutanymajorchanges.TimeandSpacearesteadyandindependentofoneanotherandanyobjectsinexistencewithinthem.

Newton’sError

IfuniverseisashowNewtondescribes,thenwhyistheskydarkatnight?

Olber’s ParadoxIfspacegoesonforeverwithstarsscatteredrandomlythroughout,theninanylineofsightinanydirectionwilleventuallyrunintoastar.Usingthislogic,theskyshouldbetheaveragebrightnessofallofthesestars;theskyshouldbeasbrightasthesun,evenatnight.

Butisn’ttheskydarkatnight…?

Yes,ofcourse- thatiswhatweobservenowandhavealwaysobserved.

SomethingiswrongwithNewton’sideaofastatic,infiniteuniverse.

Einstein’sRelativityEinsteinoverturnedpartofNewton’stheorywithhistheoriesofspecialandgeneralrelativity- timeandspacewereindeedrelated,asweretheobjectsexistingwithinthem.

SpecialRelativity

TimeandSpaceandtheirratesareintertwinedanddependonthemotionoftheobserver(1905).Inertialframesofreference(noacceleration)

Thespeedoflightisalawofphysics

Thelawsofphysicsshouldn’tchangejustdototherelativemotionofobservers.

GeneralRelativityGravitycouldn’tbemadeorremadetofitwithinSpecialRelativity.Gravitationisalawofphysics,butnotconsistentwithSpecialRelativity???Gravitybendsthefabricofspacetime- thematterthatoccupiestheuniverseinfluencestheoverallshapeofspaceandtherateoftime(1916).Non-inertialframesofreference(acceleration)andyoucan’ttellthedifferencebetweenacceleratinginanelevatorandgravity.

ImplicationsofEinstein’sIdeasBasedonthegeneralrelativityequations,thestructureofuniverseiseitheralwaysexpanding,alwayscontracting,oralwaysstatic.Toagreewiththeideasofthetime(Newton’s),Einsteinaddeda“cosmologicalconstant”whichyieldedastaticuniverse.

CosmologicalConstantRepresentsthepressurethatallowstheuniverse’sexpansiontodirectlybalancegravitationalcollapseduetotheobjectsexistingwithintheuniverse,thusyieldingastaticuniverse.Withoutthisideaofa“cosmologicalconstant”,Einsteincould’vebeenthefirsttopredictthattheuniverseisnotstatic.

Hubble’sDiscoveryEdwinHubble’sobservationsofremotegalaxies,andtheredshiftoftheirspectrallines(1924).Hubblenoticedthatthefurtherawaythegalaxy,thegreatertheredshiftofitsspectrallines.ThislinearrelationshipiscalledHubble’sLaw.

http://rst.gsfc.nasa.gov/Sect20/A9.html

RedshiftThewavelengthsofthelightemittedbydistantobjectsiselongatedasittravelstoearth.Longerthelighttravels,themoreitgetsredshifted.

http://rst.gsfc.nasa.gov/Sect20/A9.html

Hubble’sLawv=H0d

v=recessionalvelocityofthegalaxyH0 =Hubbleconstant(rateofexpansiontoday)d =distanceofgalaxytoearth

Galaxiesaregettingfartherapartastimeprogresses,thereforetheuniverseisexpanding.

Hubble’sConstantExpansionratemeasuredusingType1ASupernovae.TheageoftheuniversecanbederivedfromHubble’sconstant:◦𝑇" =

$%= $

&'$= (

&'

Forexample,ifH0 =73km/s*Mpc,thenT0 =13.4Billionyearsold

AgeofUniverseCurrently,aftertakingintoaccountdifferencesinexpansionrateovertimeandourmovementthroughspace:

T0 ~13.7± 0.2GyrAgeofstars:~13.4Gyr ± 6%

Therefore,oldeststarsareyoungerthantheageofuniverse.

HowtheUniverseExpandsThespacebetweengalaxiesexpands,notthegalaxiesthemselves;objectsheldtogetherbytheirowngravityarealwayscontainedwithinapatchofnonexpandingspace.

Example:raisinsinaloafofbread.◦ Asthedoughrises,theoverallloafofbreadexpands;thespacebetweenraisinsincreasesbuttheraisinsthemselvesdonotexpand.

CenterofUniverse?ThereisNOCENTERtotheuniverse◦ Expansionlooksthesameregardlessofwhereyouareintheuniverse.

◦ Everypointappearstobethecenteroftheexpansion,thereforenopointisthecenter.

◦ Theuniverseisinfinite.

ExpandingUniverse

ExpandingUniverse(CenterofExpansion)

ExpandingUniverse(Hubble’sLaw)

ExpandingUniverse(CenterofExpansion)

ExpandingUniverse(Hubble’sLaw)

CenterofUniverse?ThereisNOCENTERtotheuniverse◦ Expansionlooksthesameregardlessofwhereyouareintheuniverse.

◦ Everypointappearstobethecenteroftheexpansion,thereforenopointisthecenter.

◦ Theuniverseisinfinite.

EvidenceforExpansionThelightfromremotegalaxiesandotherobjectsisredshifted.Thisredshiftiscalledcosmologicalredshift becauseitiscausedbytheexpansionoftheuniverse,notbytheactualmovementoftheobject(doppler redshift).

LookbackTimeThedegreeofcosmologicalredshifttellsyouhowfarintopastyouareseeingtheobjectduetothefinitespeedoflight;thisvalueiscalledLookbacktime.However,thesevaluesarenotalwayscertainbecauseoftheexpansionofuniversewasnotalwaysconstant.

http://en.wikipedia.org/wiki/File:Hubble_ultra_deep_field_high_rez_edit1.jpg

ObservableUniverseOlber’s Paradoxissolved:duetothefinitespeedoflight,theobservableuniversedoesnotincludetheentireuniverse.Radiusoftheobservableuniversedependsontheageoftheuniverseandthespeedoflight:~47billionlightyears.Result:Skyisdarkatnightwithpointsoflight(stars,galaxies,etc.)scatteredthroughout.

OriginsoftheBigBangTheoryGeorgesLemaître (1927)expandedonideaofexpandinguniverse,realizingthattheuniversewassmalleryesterdaythantoday,andsoonuntila“daythatwouldnothavehadayesterday”:themomentofcreation.◦ Themomentofcreationwouldbethesuddenexpansionthatstartedtheexpansionoftheuniverseasweknowittoday.

Thisideawasn’twidelyacceptedatfirst:FredHoyledismissed“thishotBigBang”,notingthattherewasn’tanyrecordorremnants.Hearguedfora“steadystate”universe.

OriginsoftheBigBangTheoryAlpher &Gamow(1948)suggestedthatiftheuniversewascreatedwitha“hotBigBang”,then:◦ Variouselements,suchasHandHe,wouldbeproducedforafewminutesimmediatelyaftertheBigBangduetotheextremelyhightemperaturesanddensityoftheuniverseatthistime.

◦ Thehighdensitywouldcauserapidexpansion.◦ Astheuniverseexpanded,HandHewouldcoolandcondenseintostarsandgalaxies.

◦ Today,duetocontinuedcooling,radiationleftoverfromtheepochofrecombination,whenneutralatomsformed(~380,000yearsafterBigBang)shouldbeabout3K.

◦ ProductionofHandHeduringthistimeinsteadofjustinH-burninginstarswouldexplainwhytheH:He ratiooftheuniverseishigherthanwhatcould’vebeenproducedbystarsalone.

Gamowhumorouslydecidedtoaddthenameofhisfriend—theeminentphysicistHansBethe—tothispaperinordertocreatethewhimsicalauthorlistofAlpher,Bethe,Gamow,aplayontheGreekletters α, β,and γ (alpha,beta,gamma).

EvidencefortheBigBangTheoryGamow’stheorywasrevisted inthe1960’sbyBobDickeandJimPeeblesofPrincetonUniversity.◦ Believedthatthiscooledradiationwouldberedshiftedtothemicrowaveregionoftheelectromagneticspectrum.

◦Madeareceivertodetectthisradiation,butwereunsuccessful.

EvidencefortheBigBangTheoryTheradiation,sofarundetectedbythePrincetonteam,wasposingaproblemforNJBellTelephoneLabs,whereArnoPenziasandRobertWilsonweredevelopinganewmicrowave-satellitetechnologyforphonecalls.◦ Puzzledbysteadyhissthattheyreceivednomatterwhereintheskytheypointedtheirantenna.

◦ ThisfaintbackgroundnoisetheyweretryingtogetridofwasexactlywhatthePrincetonteamwastryingtodetect:evidenceoftheBigBang.

http://nobelprize.org/educational/physics/star_stories/overview/index.html

Signalwasnotfrombirdpoop!!!!

CMBRadiationDetectionofthisradiation,calledCosmicMicrowaveBackgroundradiation,wonPenziasandWilsontheNobelPrizeforPhysicsin1978.CMBradiationcanbedetectedbyyourtv aswell- 1%ofstaticseenonachannelthatyourtv doesn’treceiveisfromthebirthoftheuniverse.

CMBRadiationIntensityofCMBRadiationrevealsoriginsofuniverse.◦ However,difficulttodetectintensityfromEarth- theatmosphereisopaquetowavelengths10µmto1cm(CMB~1mm).

COBE(CosmicBackgroundExplorer)1989:detectoroutsidetheatmosphere:◦ MeasuredtheblackbodyspectrumofCMBradiationtobeatT=2.725K- consistentwiththeory.

◦ CMBradiationalmostentirelyisotropic;CMBisslightlywarmerindirectionofLeoandslightlycoolerindirectionofAquarius.

WMAP(WilkinsonMicrowaveAnisotropyProbe)(2002)improvedpictureofCMBRadiation.PLANCKSatelliteanevenbetterpicture

HistoricalObservationsoftheCMBandAnisotropy

CMBRadiationRadiationappearstobemostlysmooth,butthereareslightvariationsintemperaturethatshowthatmatterhadstartedtoclumpintheearlyuniverse-clumpsofmatterformedthegalaxiesandstarsseetoday.Soundwavesinearlyuniversearerecordedinthisradiation;bystudyingthecharacteristicsofthesesoundwaves,wecanfindoutabouttheconditionsoftheearlyuniverse.

http://www.pas.rochester.edu/~afrank/A105/LectureXVI/LectureXVI.html

HorizonProblemDespiteallofthesuccesswiththeBigBangTheorysofar,thehorizonproblemwasstillyettobesolved.◦ ThetemperatureoftheCMBradiationwasthe~samenomatterwhereyoulookinthesky,indicatingthatsomehowinformationlinkingallpartsoftheskywastravelingfasterthanthespeedoflight.

◦ Also,informationfromonesideoftheskyat100,000yearsold(horizonis100,000lightyearsindiameter)differedfromtheothersideoftheskyby10millionlightyears- 100timesthediameterofthehorizon.

Howisthispossible?

InflationTheoryAlanGuth (1970s)hadasolution:◦Theuniversemusthaveexpandedexponentiallyveryearlyforashortperiodoftime.◦Thiswouldaccountfortheclumpingofmatter.

EvidenceforInflationTheoryGuth predictedthattheaveragedensityoftheuniverseshouldbeequaltothecriticaldensity(6protons/m3)◦ Thiswasconfirmedbypowerfultelescopes.

EvidencefromCMBshowsthattheclumpingofmatterisconsistentwiththeamountofacceleratedexpansionduringinflation.

ExtentofInflationToday,evidenceandtheoryshowthat:AtT=10-35 sec,universed=10-24 cmBetweenT=10-35 secandT=10-32 sec,theuniverseexpandedexponentiallybyafactorof1050..Forthebriefestmoment,theuniverseexpandedfasterthanthespeedoflight.

BigBangTheory:TimelineofUniverseHubble’sLawshowsthattheuniversehasbeenexpandingforbillionsofyears- theuniverseisdenserthefurtherbackintimeyoulook.Atsomepoint,youreachaninfinitelydensepointatwhich

Tage ofuniverse=0® BigBang

T=0secondsto10-43 secondsBIGBANGoccurs.Somethingcausesinfinitelydensepointtoexpand(intoNothing).Densityofuniverseissohighthattimeandspacearecurledupandthelawsofphysicsthatweknowtodaydonotapply.Allfourforcesinnaturewereunified.ThisistimeiscalledthePlanckTime.

SeparationofForcesAfterthePlancktime,thetemperaturehaddecreased1032 Kandgravitywasthefirstforcetoseparate.Theremainingthreeforceswerestillunited- thesearetheconditionsthatparticlephysiciststodaytrytoreplicate.

T=10-35 to10-32secondsInflationcausedthesizetotheuniversetoincreaseexponentiallybyafactorof1050.Thistimeiscalledtheinflationaryepoch.

AfterInflationStopsMatteriscreated:◦ InteractionsbetweentheInflationfieldandelementaryparticlesactslikeafrictiontostoptheacceleratedexpansionandthe“heat”offrictionproduceelementaryparticlessuchasphotons,electronsandpositrons,andquarksandantiquarks.

◦ Pairproductioncontinuesuntiloneofparticlecouldnolongerbeproduced- pairannihilationhappens- result:symmetrybreaking.

◦ Reasonforslightexcessofmatteroverantimatterisbecauseofanunknownreactionknownasbaryogenesis,inwhichconservationofbaryonnumberisviolated.

◦ PairProductionoccurreduntilT=6GK,butpairannihilationhappensindependentoftemperature.

ParticleProductioninEarlyUniverseAsthesizeoftheuniverseincreasesandthetemperaturedecreases,theparticlesproducedareofdecreasingenergy.

Thefundamentalforcesandparametersofelementaryparticlesatthetimethatsymmetrywasbrokenarethesameastheyaretoday.

Thetimebetweenthebirthoftheuniverseandt=10-11 secondsisratherunknown,butwecanspeculatewhatishappeningbasedonotherobservations;beyondthistimeislessspeculativeastheseareconditionsthatparticlephysicisttrytoreplicate.

T=10-6 secondsTemperaturehascooledenoughforbaryons(Protons,Neutrons)andmesons(pions)toform.

Thestrongforcewinsoverquarks/antiquarksabilitytobounce“freely”.

Oncethetemperaturehasdecreasedenoughandhadronsformquark/antiquarkpairsarenolongermade.

Also,atthistemperature,mostparticlesarenolongermovingrelativistically,sotheuniversebecomesdominatedbythehigherenergyphotons(radiation-dominateduniverse).

T=fewminutesTemperature~1GK,density~thatofair.Neutronscombinewithprotonsmakingdeuteriumandheliumnuclei,andsomeprotonsremainindependent(hydrogennuclei).CalledBigBangnucleosynthesis.Temperatureisstilltoohightoformatomsastheywouldbeionizedimmediately.Theuniversewouldappearopaqueduringallthistimebecausephotonsandmatterwouldbeinteractingduetohightemperatures.

T=379,000yearsUniverseisnowcoolenoughthatmatterenergyisgreaterthanradiativeenergy,thusallowingatomstoform.Radiationisdecoupledfrommatterandphotonsarefree-streamedthroughoutspace- originofCMBradiation.Thistimeisknownastheepochofrecombination.Universeisnowmatter-dominated.

T~400millionyearsSinceepochofrecombination,slightlydenserregionsattractedmatternearbyandthefirststarsbegintoform.Regionscontinuetoacquirematterandotherobjectslikegalaxiesandgascloudsform.Universebeginstolooklikehowweknowittoday(stillexpandingandstillcooling).

MatterintheUniverseTodayEvidencegatheredfromCMBshowsthatallofthematterintheuniverseiscomposedofthreetypesofmatter:◦ Colddarkmatter(don’tknowwhatthisis)◦ Hotdarkmatter(neutrinos)◦ Baryonicmatter(stuffmadefromneutrons&protons)

Colddarkmatteraccountsfor~82%ofallmatterandhotdarkmatterandbaryonicmattercombinedaccountfortheremaining~18%.

NatureofExpansionToday

EvidenceofType1asupernovaeandCMBradiationshowthattheexpansionisaccelerating,drivenbydarkenergy.

Darkenergycomprises~72%ofallenergyandpermeatesallspace.

Itislikelythatthisdarkenergyhasalwaysbeenthroughouttheuniverse,butwhentheuniversewasyoungerandmuchsmaller,gravitywasstrongerthandarkenergy.

ThisaccelerationcouldbedescribedbyEinstein’scosmologicalconstant.

Today,darkenergyisstillverymisunderstood.

Expansion&FateofUniverse

http://startswithabang.com/?p=1724http://www.astronomy.com/asy/default.aspx?c=a&id=2103

FateoftheUniverse

http://www.astro.columbia.edu/~archung/labs/spring2002/lab07.html

ResearchTodayToday,particleacceleratorssuchastheLHCaretryingtoreplicateconditionsjustaftertheBigBangsothatweunderstandhowtheuniverseformed.Currently,allcosmicevolutionafterinflationaryepochcanbemodeledanddescribedprettyaccurately,butthetimebeforethis(10-15 sec)isbasicallyunknown;understandingthistimeremainsoneofthegreatestmysteriesinphysics.

RemainingQuestionsWhatisdarkmatter?Whatisdarkenergy?Candarkenergyandmatterbedetectedandstudiedinlabs?Whathappenedfromthebirthoftheuniverse,attheinstanceoftheBigBang,untiltheendoftheinflationaryepoch?WhatcausedtheBigBang?Whatistheultimatefateoftheuniverse?

phys 420: astrophysics & cosmology - home | …€¦ · · 2017-04-28redshift tells you how...

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