SNC1D6–Choo2018/19 Name:

Astrochemistry

LearningGoals/SuccessCriteria:Attheendofthislesson,Iwillbeableto:! Describewherethefirstelementscamefrom! Calculatetheageoftheuniversebasedonredshiftdata

Theamazingthingisthateveryatominyourbodycamefromastarthatexploded.

And,theatomsinyourlefthandprobablycamefromadifferentstarthanyourrighthand.ItreallyisthemostpoeticthingIknowaboutphysics:Youareallstardust.

―LawrenceM.Krauss,AUniversefromNothing:WhyThereIsSomethingRatherThanNothing

NewsFlash:BirthoftheFirstElements!Theprimordial(early)universewasaveryeventfulplace.Itwasanincrediblyhot,denseenvironmentthatcooledrapidlyastheuniverseexpanded.ThreeminutesaftertheBigBang,theuniversehadcooledenoughfornuclearfusiontotakeplace.Thisledtothecreationofthefirstatomicnucleithroughaprocesscalledprimordialnucleosynthesis.Howdidthesefirstnucleiformintheearlyuniverse?Whichelementswerecreated?Whatratioswerealltheelementspresentin?

SummaryoftheFacts

ConclusionHowwerethefirstatomicnucleiformedaftertheBigBang?Whichelementswerecreated,andhowmuchofeachelementwastherecomparedtootherelements?

Timeline of the Universe

TheSignatureoftheStarsRainbowsrevealthatwhitelightisacombinationofallthecolours.In1666,IsaacNewtonshowedthatwhitelightcouldbeseparatedintoitscomponentcoloursusingglassprisms.Soonscientistswereusingthisnewtooltoanalyzethelightcomingfromseveraldifferentlightsources.Somescientistslookedathotobjectsandgases;otherslookedatthestarsandplanets.Theyallmadeobservationsanddetectedpatterns,butittookabout250yearsforscientiststounderstandtheconnections.Part1:EveryElementHasaUniqueSignature.Everyelementemitsauniquerangeofcolourscalledanemissionspectrum.Asimilarspectrumisproducedwhenlightshinesthroughagas;however,inthiscasecertaincolours,orwavelengths,areabsorbedbythegas.Anabsorptionspectrumisthepatternofcoloursanddarklinesthatisproducedwhenlightshinesthroughagasandthegasabsorbscertainwavelengths.Thisisthesamepatternthatoccursintheemissionspectrumforthesamemedium.Figure1showssomesimplifiedabsorptionspectrallines.1. Scientistscanuseabsorptionspectratoanalyzeunknownsubstances.Identifytheelementspresent

inthesamplethatproducesthespectrainFigure2.

Part2:TheLightfromStarsContainsInformation. Thecoreofastarisveryhot(~15×106K),andveryhotobjectsglow.Thelightproducedbyastar’scorecontainsallthecoloursinthespectrum.Astronomerscanlearnmanythingsaboutastar’smotion,temperature,andcompositionbyanalyzingthestarlightthatreachesEarth.Aspectroscopeisaninstrumentthatseparateslightintoitsspectrum.Oneoftheearliestusesofthespectroscopewastoanalyzelightcomingfromastronomicalobjects.Thelightdirectedfromatelescopethroughaspectroscopeproducesanimagecalledaspectrograph.

Figure1Thelinesindicatethewavelengthsoflightthataremissingfromthelightafterpassingthroughthesample.Theweight(thickness)ofthelinesindicatestheamountoflightabsorbedatthatwavelength.Theheavier(orthicker)theline,themorelightisabsorbed.

Figure2Simplifiedabsorptionspectra

Part3:TheSpectrafromGalaxiesAreRedshifted.In1912,AmericanastronomerVestoSlipherbegantoobservemoredistantobjectsusingaspectrometer,andhenoticedthatmostofthemhadadistinctshifttowardtheredendofthespectrum.HerecognizedthisasaDopplershiftcausedbythemotionoftheobjects.Aredshiftmeansthatthesourceoflightismovingawayfromtheobserver.Figure3showsanemissionspectrumfromthequasarcalled3C273.Weseethattheemissionlinesduetohydrogenareshiftedtotheredendofthespectrum.Thelargertheredshift,thegreatertherelativemotion.

2. EdwinHubbleextendedthisobservationtomoreobjects,andforseveralobjectsplottedtheredshiftversusthedistancetotheobject.Tryitforyourself.InTable1,usetheredshiftofthespectrallinestodeterminethespeedofeachgalaxy.Todothis,usearulertoaligntheleftmostspectrallineprovidedwitheachgalaxywiththespeedscaleatthebottomofthetable.

Redshift3C 273

Comparison spectrum

RedBlue

HβHγHδ

HβHγHδ

600 nm500 nm400 nm

Figure3Redshiftedspectrumfromquasar3C273

Table1

3. PlotthespeedofeachgalaxyinTable1onthey-axisandthedistancetothegalaxyonthex-axis.Drawalineofbestfit.

4. Calculatetheslopeoftheline.Whatistheunitfortheslope?

5. TheslopeofthislineiscalledtheHubbleconstant,H0.WritetheequationforthislineusingH0asyourslope.Whatdoesittellyouabouttherelationshipbetweenthespeedofgalaxiesandtheirdistance?ThisrelationshipiscalledHubble’slaw.

6. Theageoftheuniverse,T,canbeapproximatedbytakingthereciprocal,orinverse,ofH0.Takethereciprocalofyourslope.Howoldistheuniverse(inyears)?