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Die sterre se lae metaalagtigheid en redelike hoë ruimtesnelheid dui daarop dat KOI-4878 ouer is as die son.
Maar ek weet nie hoe om 'n skatting vir die ouderdom te bereken nie.
KOI-4878-gegewens oor Simbad
Volgens Wikipedia op KOI-4878.01 niemand het nog die ouderdom van die voorwerp bereken nie, maar sê presies wat u aangehaal het:
die lae metallisiteit en redelike hoë ruimtesnelheid dui daarop dat KOI-4878 ouer is as die son.
Dit berus op die volgende bronne:
'N Soektog met die sleutelwoordKOI-4878.01op verskillende publikasie-databasisse soos arXiv of scholar.google het ook nie gehelp nie.
Verwante
- Hoe bepaal wetenskaplikes die ouderdom van sterre? fokus op die algemene vraag hoe om die ouderdom van 'n ster te bepaal.
Kan iemand die ouderdom van die KOI-4878-ster bereken? - Sterrekunde
Ek is 'n ontluikende sterrekundige en ek wou weet: die nuwe resultate van die Kosmiese Mikrogolfagtergrond het sommige sterrekundiges blykbaar oortuig dat die heelal ongeveer 13,8 miljard jaar oud is. Dit klink egter baie soos absolute tyd. As tyd in verskillende rame anders gemeet word, hoe kan die heelal net een ouderdom hê?
Of op dieselfde manier lyk dit asof die oudste meteoriete 'n absolute ouderdom van 4,56 miljard jaar impliseer. Maar hoe kan dit 'die' ouderdom van die sonnestelsel wees as identiese horlosies teen verskillende tempo's tik, afhangende van hul afstand tot die son? Moet meteoriete van Mercurius, sê ons, nie jonger ouderdomme vertoon as gevolg van stadiger radioaktiewe horlosies nie? Baie dankie.
Dit is regtig 'n interessante vraag! U het gelyk dat vanweë algemene relatiwiteit, sal horlosies in 'n gravitasieveld stadiger loop. Daarom sal klippe nader aan die son horlosies hê wat stadiger tik as rotse verder weg, en dus sal Mercuriusgesteentes teoreties jonger wees. As u egter uitvind wat die verskil in tariewe is, is dit 'n baie klein effek, selfs gedurende die hele geskiedenis van die Sonnestelsel.
As ek byvoorbeeld 'n eenvoudige berekening (met die veronderstelling van 'n swak swaartekragveld, wat OK is vir die son) gebruik, om die tydverwyding vanaf die sonoppervlak te bereken, vind ek dat horlosies op die sonoppervlak stadig sal verloop met 6 sekondes per jaar vergeleke met horlosies in die verre ruimte. In werklikheid sal die verskil tussen gesteentes op die afstand van Mercurius en die afstand van, byvoorbeeld, die asteroïde gordel kleiner wees as dit - die 6 sekondes per jaar is die grootste wat u oor die sonnestelsel sou verwag. Maar kom ons gebruik hierdie groot aantal om te sien wat gebeur.
Ons dink die ouderdom van die sonnestelsel is ongeveer 4,5 miljard jaar, dus sal die verskil in tyd wat aan die oppervlak van die son gemeet word en die tyd wat in die diep ruimte gemeet word, ongeveer 850 jaar wees gedurende die tydperk. Aangesien die verskil eintlik van plek tot plek regdeur die sonnestelsel minder is, moet die ware getal selfs kleiner wees. Ons weet nie hoe oud die sonstelsel is met 'n paar honderd jaar akkuraatheid nie, hoewel dit indrukwekkend sou wees! Al ons dateringstegnieke bevat foute, en ook die meteoriete wat ons dateer, het op effens verskillende tye gevorm. Daarbenewens kan asteroïdes in die sonnestelsel rondbeweeg het, wat sou verander hoe stadig hul radioaktiewe klokke gaan. Ek dink dus dit is teoreties moontlik dat die algemene relatiwiteitseffek in die toekoms ons vermoë om sonnestelselmateriaal te dateer, kan beperk, maar ek dink ons het waarskynlik wonderlike tegnologie nodig voordat dit 'n probleem word. (Ek dink planetêre wetenskaplikes sal baie bly wees as hulle hulle hieroor moet bekommer as hulle met mekaar uitgaan!)
Dieselfde argument geld vir die heelal. Alhoewel die heelal baie ouer is, het ons ook groter foute oor wat ons dink die ware ouderdom is. Die feit dat ons dinge meet vanuit die son se swaartekragomgewing, gee ons slegs 'n klein meetfout. U het dus reg dat die ouderdomme van dinge sal verskil, afhangende van die verwysingsraamwerk, maar die effek is klein genoeg om nie mee te meet met die onakkuraathede in ons meetvermoë nie.
Hoe weet ons die ouderdom van die heelal?
Beeldkrediet: ESA / Hubble & amp NASA Erkenning: Judy Schmidt.
As ons die antwoord op 'n vraag soos 'wat is die ouderdom van die heelal' in 'n ideale wêreld wil ontdek, sal ons ongelooflike aantal onafhanklike bewyse hê, wat almal dieselfde antwoord het. Maar in werklikheid is daar net twee goed, en die een is beter as die ander.
Die 'goeie' is om na te dink oor die feit dat ons heelal vandag uitbrei en afkoel, en om te besef dat dit in die verlede dus warmer en digter was. As ons teruggaan na vroeër en vroeër tye, sou ons vind dat, aangesien die volume van die heelal kleiner was, al die materie daarin nie net nader aan mekaar was nie, maar dat die golflengtes van al die individuele fotone (ligdeeltjies) daarin was korter, want die uitbreiding van die heelal het hulle so lank soos vandag gedoen.
Beeldkrediet: NASA / GSFC / Dana Berry.
Aangesien die golflengte van 'n foton sy energie en temperatuur definieer, is 'n foton met 'n korter golflengte meer energiek en hoër in temperatuur. Namate ons al hoe langer teruggaan in die tyd, styg die temperatuur op en op, totdat ons op 'n stadium die vroegste stadiums van die warm oerknal bereik. Dit is belangrik: daar is 'n "vroegste verhoog" vir die warm oerknal!
As ons "oneindig" ver ekstrapoleer, sou ons 'n enkelheid bereik, waar fisika afbreek. Met ons moderne begrip van die heel vroeë Heelal, weet ons dat 'n inflasionêre staat die warm, digte oerknal voorafgegaan het, en dat die inflasionêre staat van onbepaalde duur was. As ons dus praat van 'die eeu van die Heelal', praat ons oor hoeveel tyd verloop het sedert die heelal die eerste keer deur die warm oerknal tot vandag toe beskryf kon word.
Beeldkrediet: Bock et al. (2006, astro-ph / 0604101) wysigings deur E. Siegel.
As u 'n heelal soos ons het, is dit onder die wette van algemene relatiwiteit:
- van eenvormige digtheid op die grootste skaal,
- wat op alle plekke dieselfde wette en algemene eienskappe het,
- wat in alle rigtings dieselfde is, en
- waarin die oerknal op een slag oral op alle plekke plaasgevind het,
dan is daar 'n unieke verband tussen hoe oud die Heelal is en hoe dit deur sy geskiedenis uitgebrei word.
Beeldkrediet: NASA, ESA en A. Feild (STScI).
Met ander woorde, as ons kan meet hoe die heelal vandag uitbrei en hoe dit deur sy hele geskiedenis uitgebrei het, kan ons presies weet wat al die verskillende komponente is waaruit dit bestaan. Ons leer dit uit 'n hele aantal waarnemings, insluitend:
Beeldkrediet: ESA / Hubble en NASA, via http://www.spacetelescope.org/images/potw1004a/.
- Van direkte metings van die helderheid en afstande van voorwerpe in die heelal, soos sterre, sterrestelsels en supernovas, sodat ons die kosmiese afstandsleer kan konstrueer.
Beeldkrediet: Sloan Digital Sky Survey.
- Van metings van grootskaalse strukture, die samevoeging van sterrestelsels en van barioon-akoestiese ossillasies.
Beeldkrediet: ESA en die Planck-samewerking.
- En as gevolg van die skommelinge in die kosmiese mikrogolfagtergrond, 'n 'momentopname' van die heelal toe dit slegs 380 000 jaar oud was.
U sit al hierdie dinge bymekaar, en u kry 'n heelal wat saamgestel is, vandag, van 68% donker energie, 27% donker materie, 4,9% normale materie, ongeveer 0,1% neutrino's, ongeveer 0,01% bestraling, en feitlik niks anders nie. Maar jy gooi in hoe die heelal vandag uitbrei, en ons kan dit in die tyd ekstrapoleer en die hele uitbreidingsgeskiedenis van die heelal, en dus sy ouderdom, leer.
Die verskillende energiekomponente van die Heelal en wanneer / hoe dit saak maak. Beeldkrediet: E. Siegel.
Die getal wat ons kry - presies van Planck, maar aangevul deur ander bronne soos supernovametings, die HST-sleutelprojek en die Sloan Digital Sky Survey - is dat die heelal 13,81 miljard jaar oud, met 'n onsekerheid van net 120 miljoen jaar. Dit beteken dat ons vol vertroue is in die era van die heelal tot 99,1% akkuraatheid, wat 'n wonderlike prestasie is!
Ja, ons het 'n aantal verskillende datastelle wat op hierdie gevolgtrekking dui, maar in werklikheid is dit almal dieselfde metode. Ons is eenvoudig gelukkig dat daar 'n konsekwente prentjie is waarna almal verwys, maar in werklikheid is enige van die beperkings self onvoldoende om te sê "dit is presies hoe die Heelal is." In plaas daarvan bied hulle almal 'n verskeidenheid moontlikhede, en dit is slegs hul kruising wat ons vertel waar ons woon.
Beeldkrediet: Suzuki et al. (The Supernova Cosmology Project), aanvaar vir publikasie, Ap.J.,. [+] 2011., via http://supernova.lbl.gov/Union/.
As die Heelal vandag dieselfde huidige eienskappe het, maar bestaan uit 100% normale materie en geen donker materie of donker energie nie, sou ons Heelal net 10 miljard jaar oud wees. As die heelal 5% normale materie was (sonder donker materie of donker energie) en die Hubble-konstante 50 km / s / Mpc was in plaas van 70 km / s / Mpc, sou ons heelal maar liefst 16 miljard jaar oud wees. Met die kombinasies van dinge wat ons vandag het, kan ons egter met vertroue sê 13,81 miljard jaar is die ouderdom van die heelal, met 'n baie klein onsekerheid. Dit is 'n ongelooflike prestasie van wetenskap.
En tog is dit alles regmatig een metode. Dit is die belangrikste, dit is die beste, dit is die mees volledige, en dit het 'n klomp verskillende bewyse wat daarop wys. Maar daar is nog een, en dit is ongelooflik nuttig vir nagaan ons resultate.
Beeldkrediet: Joel D. Hartman, Princeton Universiteit, via. [+] http://www.astro.princeton.edu/
Dit is die feit dat ons weet hoe sterre leef, deur hul brandstof verbrand en sterf. In die besonder weet ons dat alle sterre, wanneer hulle lewendig is en deur hul hoofbrandstof verbrand (wat waterstof in helium versmelt), 'n spesifieke helderheid en kleur het, en by die spesifieke helderheid en kleur bly. enigste vir 'n sekere tyd: totdat die kern van hul kern begin opraak. Op daardie stadium begin die helderder, blouer en hoër massa sterre van die hoofreeks "afskakel" (die geboë lyn op die kleurgrootte-diagram hieronder) en ontwikkel dit tot reuse en / of superreuse.
Beeldkrediet: Richard Powell onder c.c.-by-s.a.-2.5 (L) R. J. Hall onder c.c.-by-s.a.-1.0 (R).
Deur te kyk waar die uitdraaipunt is vir 'n sterretros wat almal gelyktydig gevorm het, kan ons uitvind - as ons weet hoe sterre werk - hoe oud daardie sterre in die groep is. As ons na die oudste bolvormige trosse daarbuite, die minste in swaar elemente en waarvan die afskakeling vir die sterre met die laagste massa daar buite kom, vind ons dat hulle redelik konsekwent op 'n ouderdom van ongeveer 13,2 miljard jaar kom, maar nie veel ouer nie. (Daar is beduidende onsekerhede van ongeveer 'n miljard jaar hieroor, let wel.)
Globusgroep Messier 10, soos afgebeeld met die Hubble-ruimteteleskoop. Beeldkrediet: ESA / Hubble & amp. [+] NASA.
Ouderdomme van 12 miljard jaar en ouer is baie algemeen, maar ouderdomme van byvoorbeeld 14 miljard jaar en ouer is ongehoord, hoewel daar in die negentigerjare 'n tydperk was waarin die ouderdomme van 14-16 miljard jaar dikwels aangehaal is. ('N Verbeterde begrip van sterre en hul evolusie het hierdie getalle afgebreek.)
Al met al het ons twee metodes - een uit ons kosmiese geskiedenis en een om plaaslike sterre te meet - wat wys dat ons heelal se ouderdom tussen 13 en 14 miljard jaar oud is. Dit sal niemand verbaas as ons blykbaar so min as 13,6 of soveel as 14,0 miljard jaar oud is nie, of miskien selfs so min as 13,5 of soveel as 14,1 miljard. Maar ons is nie 13,0 of 15,0 miljard jaar oud, en ons het dit met uiterste sekerheid vasgestel. Sê dat ons met vertroue 13,8 miljard jaar oud is, en nou weet u hoe ons dit uitgevind het!
Sterrekundiges ontdek die verband tussen rotasiesnelheid van sterre, hul ouderdomme
Dr Soren Meibom, 'n sterrekundige by die Harvard-Smithsonian Sentrum vir Astrofisika, en sy kollegas uit Duitsland en die Verenigde State sê dat hulle die ouderdom van 'n ster presies kan bepaal uit hoe vinnig dit draai.
NGC 6819. Beeldkrediet: Roberto Mura / CC BY-SA 3.0.
Om die ouderdomme van sterre te kan vertel, is die basis om te verstaan hoe sterrekundige verskynsels wat sterre en hul metgeselle betrek, mettertyd ontvou.
Om 'n ster en ouderdom te ken, is veral relevant vir die soeke na tekens van uitheemse lewe buite ons sonnestelsel. Dit het lank geneem vir die lewe op aarde om die kompleksiteit wat ons vandag vind, te bereik.
Met 'n akkurate sterrehorlosie kan sterrekundiges sterre identifiseer met planete wat so oud soos ons son of ouer is.
Die nuwe studie, gepubliseer in die tydskrif Aard, toon dat daar 'n noue wiskundige verband is tussen massa, draai en ouderdom, sodat sterrekundiges die derde kan bereken deur die eerste twee te meet.
"Ons het gevind dat die verband tussen massa, rotasiesnelheid en ouderdom nou goed gedefinieër word deur waarnemings dat ons die ouderdomme van individuele sterre binne tien persent kan behaal," het dr Sydney Barnes van die Leibniz-instituut vir astrofisika in Duitsland gesê, wat is 'n mede-outeur van die studie.
Dr Barnes het hierdie metode die eerste keer in 2003 voorgestel, en voortgebou op vorige werk, en dit gyrochronologie genoem.
Om 'n ster se draai te meet, kyk die sterrekundiges na veranderings in sy helderheid wat veroorsaak word deur donker kolle op die oppervlak en die sterrekwivalent van sonvlekke.
In teenstelling met ons son, is 'n ster in die verte 'n onopgeloste ligpunt, sodat sterrekundiges nie 'n sonvlek oor die stertskyf kan sien nie. In plaas daarvan kyk hulle of die ster effens verdof wanneer 'n sonvlek verskyn, en verhelder weer wanneer die sonvlek buite sig draai. Hierdie veranderinge is baie moeilik om te meet, want 'n tipiese ster verdof met veel minder as 1%, en dit kan dae neem voordat 'n sonvlek oor die gesig van die ster gaan.
Dr Barnes, dr Meibom en hul mede-outeurs het die prestasie behaal met behulp van data van NASA se Kepler-teleskoop, wat presiese en deurlopende metings van die helder helderheidslyste gegee het.
Om die ouderdom van gyrochronologie akkuraat en akkuraat te hou, moet hulle hul nuwe horlosie kalibreer deur die draaiperiodes van sterre met beide bekende ouderdomme en massas te meet.
In hul nuwe studie het die span sterre in die 2,5 miljard jaar oue groep bekend as NGC 6819 ondersoek.
"Ouer sterre het minder en kleiner kolle, wat hul periodes moeiliker opspoor," het dr Meibom gesê.
Die sterrekundiges het sterre van 80 tot 140 persent soveel as die son ondersoek. Hulle kon die draaie van 30 sterre meet met periodes wat wissel van 4 tot 23 dae, vergeleke met die huidige 26 dae-draai-periode van die Son.
Die agt sterre in NGC 6819, wat baie ooreenstem met die son, het 'n gemiddelde draaitydperk van 18,2 dae, wat sterk impliseer dat die son & # 8217; s tydperk ongeveer die waarde was toe dit 2,5 miljard jaar oud was.
Die wetenskaplikes evalueer dan verskeie rekenaarmodelle wat die draaispoed van sterre bereken op grond van hul massa en ouderdom, en bepaal watter model die beste by hul waarnemings pas.
& # 8220Nou kan ons presiese ouderdomme aflei vir 'n groot aantal koel veldsterre in ons Melkwegstelsel deur hul draaiperiodes te meet. Dit is 'n belangrike nuwe instrument vir sterrekundiges wat die evolusie van sterre en hul metgeselle bestudeer, en een wat kan help om planete te identifiseer wat oud genoeg is om die komplekse lewe te kan ontwikkel, 'het dr Meibom gesê.
Søren Meibom et al. 'N Afdraaiklok vir koel sterre uit waarnemings van 'n 2,5 miljard jaar oue tros. Aard, aanlyn gepubliseer op 5 Januarie 2015 doi: 10.1038 / nature14118
Kan ons na 'n parallelle heelal ontsnap?
Wetenskaplikes sê daar is twee moontlike toekoms van die heelal. Die eerste is dat die heelal uiteindelik teenoor die oerknal op homself sal instort. Hierdie proses word die 'Big Crunch' genoem. 'N Ander opsie is dat ons heelal sal eindig in 'n' Big Freeze ', wat ook bekend staan as die Heat Death.
Die meeste sterrekundiges en ander wetenskaplikes glo dat ons heelal eendag in 'n 'groot vriespunt' sal eindig. Beteken dit dat dit die einde van alles is?
Soos anomalien.com op Facebook
Om in kontak te bly en ons nuutste nuus te kry
Anders as baie natuurkundiges, dink dr Michi Kaku dat ons hierdie lot moontlik sal kan vermy deur in 'n parallelle heelal in te gly "op dieselfde manier as wat Alice in die lykglas gekom het om Wonderland binne te gaan."
Ons het vroeër berig dat sterrekundiges die eerste bewys van parallelle heelalle gevind het. Dus, miskien is die idee dat ons uit ons eie heelal kan ontsnap en 'n ander werklikheid kan betree, tog nie so vergesog nie.
Een manier om die uitbreiding van die heelal te bestudeer, is om die Doppler-verskuiwing te ondersoek, verduidelik dr. Kaku in sy video.
Hy sê dat 'as ons in die hemel kyk, kyk ons na sterlig wat uit die sterrestelsels afgelei word en vind dat die lig effens rooierig is. Rooier as wat dit veronderstel is om te wees. Dit beteken dat hierdie voorwerpe, die reusagtige sterrestelsels van ons af wegbeweeg en daarom brei die heelal uit.
Wel, ons kan die videoband agteruit laat loop, en deur die videoband agteruit te laat loop, kan ons dan bereken wanneer al hierdie sterrestelsels van een punt af kom. En dit is hoe ons die ouderdom van die heelal bereken, deur eenvoudig op die terugspoelknop te druk wanneer ons die uitbreiding van die heelal bereken.
Deur die videoband agteruit te laat sien, sien ons dat die heelal ongeveer 13,7 miljard jaar oud is, plus minus 1%.
Ons weet dus nou die ouderdom van die heelal. 13,7 miljard jaar deur die videoband agteruit te laat loop.
Maar wat gebeur as ons vinnig vorentoe slaan. Wat gebeur as ons miljarde jare vooruit gaan? Wel, hier word dit donkerder.
Maar deur te ontleed hoe die heelal in die verlede uitgebrei het, het ons gedink dat die heelal stadiger word.
Ons het vroeër gedink die heelal word ouer en daarom vertraag dit die stoom. Verkeerde. Ons glo nou dat die heelal versnel.
Dit versnel eintlik, in die weghol-modus, wat beteken dat ons in plaas van sterf in 'n groot geknars waarskynlik in 'n groot vriespunt sal sterf. Ons is nie positief nie. Ons weet nie of dit miljarde jare sal aanhou nie. Maar as dit so is, is die heelal in 'n weghol-modus.
Dit beteken dat ons eendag, miskien as ons na die naghemel kyk, amper niks sal sien nie, want die sterrestelsels in die verte is so ver dat lig nie eers ons teleskope kan bereik nie. Nie 'n aangename gedagte nie. Maar ons heelal kan uiteindelik in 'n groot vriespunt sterf eerder as in 'n groot geknars. '
Natuurlik sal dit lank duur voordat die heelal in 'n groot vriespunt eindig, maar niemand weet regtig wanneer dit kan gebeur nie.
'Niemand weet wanneer hierdie groot bevriesing sal plaasvind of of dit ooit sal plaasvind nie. Daar is egter ramings gemaak, miskien honderde miljarde jare, miskien triljoene jare. Eendag sal dit so koud word dat jy na die naghemel sal kyk en dit sal amper heeltemal swart wees.
Al die sterre sal al hul kernbrandstof opgebruik het, die heelal sal bestaan uit neutronsterre, dooie swart gate, die temperatuur sal bykans nul wees en op daardie stadium kan selfs die bewussyn, selfs die gedagte self, nie bestaan nie, en sommige mense dink dat miskien die wette van fisika 'n doodsbevel is vir alle intelligente lewe dat ons almal gaan sterf as die heelal vries ”, sê dr. Kaku.
Dit is die slegte nuus, maar daar is ook goeie nuus. As ons aanvaar dat die mensdom nog bestaan en 'n baie hoër tegnologiese vlak bereik, is dit moontlik om te oorleef deur na 'n ander parallelle heelal te ontsnap.
Dr Kaku sê: 'daar is 'n leemte in die wette van fisika. Oor triljoene jare van nou sal die intelligente lewe miskien in staat wees om die 'Planck Energy' te noem. Die Planck-energie is die ultieme energie. Dit is die energie van die oerknal. Dit is die energie waarmee swaartekrag self begin afbreek.
U weet dat as u 'n mikrogolfoond het en u dit opwarm, u gewone water kan neem en laat kook, ys kan smelt, water kan kook. Maar wat gebeur as jy die mikrogolfoond nog meer laat draai?
Uiteindelik begin die stoom opbreek in suurstof en waterstof. As u dit nog meer opdraai, vorm ione ewe skielik atome wat uitmekaar ruk. En as u die mikrogolfoond nog meer opskakel, dan begin selfs die kern uitmekaar breek en kry u 'n plasma protone en neutrone. As jy dit nog meer opdraai, kry jy 'n gluonplasma. En as u dit nog so kronkel met hierdie ongelooflike energie.
Tien tot die 19 miljard elektron volt is ons nie seker nie, maar miskien begin selfs die ruimte self kook. Selfs ruimtetyd word onstabiel. Borrels begin vorm by hierdie Planck Energy. En miskien is hierdie borrels poortjies. Porte na 'n parallelle heelal.
Ons is natuurlik nie seker hieroor nie. Hierdie suiwer bespiegeling, maar daar is teorieë wat sê dat daar heelal langs ons heelal kan wees. En in werklikheid sal die Large Hadron Collider ons die eerste eksperimentele bewys lewer oor die bestaan van parallelle heelalle.
Dink aan ons as miere wat op 'n vel papier woon, maar miskien is daar ander parallelle velle papier met ander miere wat daarop woon. En miskien is ons baie naby aan hierdie ander heelalle, maar ons kan dit nie bereik nie. Die energie wat nodig is om 'n parallelle heelal te bereik, is die Planck Energy, 10 tot 19 miljard elektron volt.
Ek sou veronderstel dat triljoene jare van nou af, die intelligente lewe, wat die uiteindelike ondergang van die heelal in die gesig staar, kan besluit om die heelal te verlaat. Om ons heelal te verlaat en 'n parallelle heelal te betree op dieselfde manier as wat Alice in die lykglas gekom het om Wonderland binne te gaan. '
Hoe bereken wetenskaplikes die ouderdom van planete, sterre en sterrestelsels?
Ek het hieroor op Google probeer soek, insluitend die ouderdom van die Heelal, en die bronne het aanhoudend gesê dat ons dit kan sien uit die ouderdom van die sterre en sterrestelsels rondom ons. Hoe kan sterrekundiges uitvind hoe oud sterre en sterrestelsels is?
Ek lees ook dat ons Melkwegstelsel 100.000 ligjaar en 1000 ligjare dik is. Hoe kan wetenskaplike dit ook agterkom?
Ek neem aan dat u die wikipedia-inskrywing oor & quotation of the universe. & Quot lees, wat 'n goeie vertrekpunt is. Daaruit moet u ten minste opmerk dat die ouderdom gebaseer is op hoe vinnig die heelal uitbrei. As ons weet hoe ver alles van ons af is en hoe vinnig dit beweeg (insluitend die versnelling daarvan), gaan ons agteruit om uit te vind hoeveel tyd dit geneem het om daardie sterrestelsels daar te bereik. Presto! 13,8 miljard jaar.
Om u kennis te vergroot oor hoe die wetenskap tot op daardie stadium gekom het, wil u dalk met nog 'n aantal wikipedia-inskrywings begin: cepheid veranderlike sterre, tipe IA-supernova Shapely Curtis-debat en eilandheeldebat.
Teen die vroeë 1920's het wetenskaplikes gestry oor hoe groot ons sterrestelsel was, en baie van hulle het gedink dat ons sterrestelsel dieselfde was as die heelal. Al die sterre en newels was almal in ons sterrestelsel en miskien is dit 10 000 ligjare breed. Ingesluit in al hierdie dinge was sogenaamde & # x27spiraalnevel. & Quot Wat die meeste gedink het dieselfde was as die gewone newel, bv. Perdekopnevel, Orionnevel, Arendnevel ens. Dit is basies gas / stofwolke wat duisende ligjare (ly) van ons af is.
Maar uiteindelik kon Hubbel die lig meet van veranderlike sterre van die cepheid in die spiraalnewels wat voorgestel het dat hulle baie verder weg was as 10 000 ly. dit het te make met die eilanddebat en die Shapely Curtis-debat, wat u kan google. Hubbel en Curtis ondersteun die idee dat hierdie spiraalnewels regtig buite ons sterrestelsel was. Shapely het gesê dat dit geen sin het nie, want hulle sou ongeveer 100 miljoen ligjare moes wees en niemand glo dit nie. En ook dat die nova-sterre binne hulle super helder sal moet wees om ons tot hier te sien (hulle is so helder, dit is supernovas). jy kan die res google. (Vormig het die ligging van ons son in die sterrestelsel uitgevind, so hy was ook 'n slim man)
Cepheid veranderlike sterre is gekategoriseer deur 'n dame genaamd Henrietta Swan Leavitt wat by Harvard gewerk het. sy het agtergekom dat hoe langer hulle dit neem om helderder en dowwer te word (die & quotperiod & quot). Nie net hoe helder dit vir ons lyk nie, maar hul absolute helderheid of helderheid.
Om dit uit te vind, bestudeer sy al die kepheids wat binne die Magellaanse wolke was. Destyds 'n soort newel, maar ons ken hulle as onreëlmatige sterrestelsels, die naaste sterrestelsels aan ons. Omdat hulle almal in dieselfde wolk was, was hulle almal op dieselfde afstand tot ons (weereens miskien 10.000 ly, het hulle gedink). Hulle was dus almal op dieselfde afstand en die helder een het langer gehad en die dowwer korter. Daarom het sy 'n grafiek saamgestel oor hoe helder so 'n veranderlike was op grond van hoe lank die tydperk was.
Dit het 'n soort heerser geword om afstande te meet en te sê dat u 'n Cepheid in 'n ander sterrestelsel vind, en dit word elke maand helderder en verdof. U soek dit op die grafiek en sien dat dit veronderstel is om 4 kerse in helderheid te wees (as ons aanvaar dat dit dieselfde afstand is as die Cepheid-veranderlikes in die Henriettas-grafiek). Maar in plaas daarvan is dit net 1 kers helder. Dit moet twee keer die afstand wees as die standaard, want die helderheid daal as die kwadraatwaarde van die afstand (dus op twee keer die afstand is dit die helderheid 1/4).
Dit is die basiese konsep in die meeste van hierdie maatstawwe om te meet.
Uiteindelik eindig die gevormde Curtis-debat deur vas te stel dat hierdie & spiraalagtige newels & quot regtig ander sterrestelsels was. Hulle gebruik die cepheidveranderlikes om die afstand te meet. Later in 1943 was Walter Baade die eerste wat 'n ster buite ons eie sterrestelsel gesien het. Hubbel het blykbaar 20 jaar tevore die lig van die veranderlike sterre in Andromeda ens. Opgetel sonder om die ster self te sien, soos ek dit verstaan. Natuurlik het dit net die teorie van sterrestelsels bevestig.
Cepheid-veranderlikes kan volgens my tot 50 miljoen ly gebruik word, nou gebruik hulle die helderheid van tipe IA-supernova om afstande groter as dit te bepaal. hierdie keer het hulle wiskunde gebruik om presies te verstaan wat 'n supernova is en waaruit dit bestaan, en hoe helder dit moet wees en hoe lank dit moet wees of hoe die helderheid daarvan mettertyd sal verander. As hulle dan sien hoe een afgaan, meet hulle die helderheid / periode en dit vertel hoe ver dit is, want dit sal dowwer wees.
Die supernovametode is dus 'n manier om afstande te meet wat ek tot 1 miljard ly dink.
Toe hulle eers agterkom dat cepheidveranderlikes 'n periode / helderheidsverhouding het, het hulle spiraalstelsels bestudeer om vas te stel dat hulle buite ons sterrestelsel is. Hulle het Cepheid-veranderlikes gebruik om die plaaslike sterrestelsels en supernova's te meet om die verste te meet.
Inhoud
Die tradisionele naam Aldebaran is afgelei van die Arabies al Dabarān ("الدبران"), wat "die volgeling" beteken, omdat dit blykbaar die Pleiades volg. [15] [16] In 2016 het die International Astronomical Union Working Group on Star Names (WGSN) die eienaam goedgekeur Aldebaran vir hierdie ster. [17] [18]
Aldebaran is die helderste ster in die sterrebeeld Taurus en so ook die Bayer-benaming α Tauri, gelatiniseer as Alpha Tauri. Dit het die Flamsteed-benaming 87 Tauri as die 87ste ster in die konstellasie van ongeveer 7de magnitude of helderder, georden volgens regs hemelvaart. Dit het ook die Bright Star-katalogus nommer 1457, die HD nommer 29139, en die Hipparcos katalogus nommer 21421, meestal gesien in wetenskaplike publikasies.
Dit is 'n veranderlike ster wat in die Algemene Katalogus van veranderlike sterre gelys word, maar dit word gelys volgens die Bayer-benaming en het nie 'n aparte benaming vir veranderlike sterre nie. [4]
Aldebaran en verskeie nabygeleë sterre word opgeneem in dubbelster-katalogusse, soos die Washington Double Star Catalogue as WDS 04359 + 1631 en die Aitken Double Star Catalogue as ADS 3321. Dit is saam met 'n metgesel van die 11de grootte as 'n dubbelster as H IV 66 opgeneem. in die Herschel Catalogue of Double Stars en Σ II 2 in die Struve Double Star Catalogue, en saam met 'n ster van die 14de grootte as β 550 in die Burnham Double Star Catalogue. [19] [20]
Aldebaran is een van die maklikste sterre om in die naghemel te vind, deels vanweë die helderheid daarvan en deels omdat dit naby een van die meer opvallende sterretjies in die lug is. Na die drie sterre van Orion se gordel in die teenoorgestelde rigting van Sirius, is Aldebaran die eerste helder ster. [21]
Die ster is toevallig in die siglyn tussen die Aarde en die Hyades, en dit lyk dus asof dit die helderste lid van die oop tros is, maar die tros wat die bul-kopvormige asterisme vorm, is meer as twee keer so ver weg, ongeveer 150 ligjare. [22]
Aldebaran is 5,47 grade suid van die ekliptika en kan dus deur die maan verberg word. Sulke okkulasies vind plaas wanneer die stygende knoop van die maan naby die herfs-ewening is. [23] 'n Reeks van 49 okkultasies het op 29 Januarie 2015 plaasgevind en op 3 September 2018 geëindig. [24] Elke gebeurtenis was sigbaar vanaf punte in die noordelike halfrond of naby die ewenaar mense in bv. Australië of Suid-Afrika kan nooit 'n Aldebaran-okkultasie waarneem nie, want dit is te ver suid van die ekliptika. 'N Redelike akkurate skatting van die deursnee van Aldebaran is tydens die okkulasie van 22 September 1978 verkry. [25] Aldebaran is in samewerking met die Son rondom 1 Junie van elke jaar. [26]
Met 'n byna-infrarooi J-bandsterkte van -2,1 is slegs Betelgeuse (-2,9), R Doradus (-2,6) en Arcturus (-2,2) helderder op die golflengte. [7]
Op 11 Maart 509 AD is 'n maan okkultasie van Aldebaran in Athene, Griekeland, waargeneem. [27] Die Engelse sterrekundige Edmund Halley het die tydsberekening van hierdie gebeurtenis bestudeer en in 1718 tot die gevolgtrekking gekom dat Aldebaran sedert daardie tyd van posisie moes verander het, en 'n paar minute boog verder na die noorde beweeg het. Dit, sowel as waarnemings van die veranderende posisies van die sterre Sirius en Arcturus, het gelei tot die ontdekking van behoorlike beweging. Op grond van hedendaagse waarnemings het die posisie van Aldebaran 7 ′ in die afgelope 2000 jaar verskuif, ongeveer 'n kwart van die deursnee van die volmaan. [28] [29] Vanweë presessie van die equinoxes, was die equinox (Noordelike Halfrond) | landelike equinox naby Aldebaran. [30]
Die Engelse sterrekundige William Herschel het in 1782 'n dowwe metgesel vir Aldebaran ontdek [31] 'n ster van die 11de grootte met 'n hoekskeiding van 117 ″. Hierdie ster is blykbaar self 'n noue dubbelster deur S. W. Burnham in 1888, en hy het 'n bykomende metgesel van die 14de grootte ontdek met 'n hoekskeiding van 31 ″. Die metings van die regte beweging het getoon dat Herschel se metgesel van Aldebaran afwyk en dat hulle dus nie fisies verbind was nie. Die metgesel wat Burnham ontdek het, het egter byna presies dieselfde beweging gehad as Aldebaran, wat daarop dui dat die twee 'n wye binêre sterstelsel gevorm het. [32]
William Huggins het in 1864 by sy private sterrewag in Tulse Hill, Engeland, die eerste studies van die spektrum van Aldebaran uitgevoer, waar hy die lyne van nege elemente kon identifiseer, waaronder yster, natrium, kalsium en magnesium. In 1886, Edward C. Pickering at the Harvard College Observatory used a photographic plate to capture fifty absorption lines in the spectrum of Aldebaran. This became part of the Draper Catalogue, published in 1890. By 1887, the photographic technique had improved to the point that it was possible to measure a star's radial velocity from the amount of Doppler shift in the spectrum. By this means, the recession velocity of Aldebaran was estimated as 30 miles per second (48 km/s), using measurements performed at Potsdam Observatory by Hermann C. Vogel and his assistant Julius Scheiner. [33]
Aldebaran was observed using an interferometer attached to the Hooker Telescope at the Mount Wilson Observatory in 1921 in order to measure its angular diameter, but it was not resolved in these observations. [34]
The extensive history of observations of Aldebaran led to it being included in the list of 33 stars chosen as benchmarks for the Gaia mission to calibrate derived stellar parameters. [35] It had previously been used to calibrate instruments on board the Hubble Space Telescope. [13]
Aldebaran is listed as the spectral standard for type K5+ III stars. [6] Its spectrum shows that it is a giant star that has evolved off the main sequence band of the Hertzsprung–Russell diagram after exhausting the hydrogen at its core. The collapse of the centre of the star into a degenerate helium core has ignited a shell of hydrogen outside the core and Aldebaran is now on the red giant branch (RGB). [5]
The effective temperature of Aldebaran's photosphere is 3,910 K . It has a surface gravity of 1.59 cgs , typical for a giant star, but around 25 times lower than the Earth's and 700 times lower than the Sun's. Its metallicity is about 30% lower than the Sun's.
Measurements by the Hipparcos satellite and other sources put Aldebaran around 65.3 light-years (20.0 parsecs) away. [10] Asteroseismology has determined that it is about 16% more massive than the Sun, [11] yet it shines with 518 times the Sun's luminosity due to the expanded radius. The angular diameter of Aldebaran has been measured many times. The value adopted as part of the Gaia benchmark calibration is 20.580 ± 0.030 mas . [13] It is 44 times the diameter of the Sun, approximately 61 million kilometres. [36]
Aldebaran is a slightly variable star, assigned to the slow irregular type LB. The General Catalogue of Variable Stars indicates variation between apparent magnitude 0.75 and 0.95 from historical reports. [4] Modern studies show a smaller amplitude, with some showing almost no variation. [37] Hipparcos photometry shows an amplitude of only about 0.02 magnitudes and a possible period around 18 days. [38] Intensive ground-based photometry showed variations of up to 0.03 magnitudes and a possible period around 91 days. [37] Analysis of observations over a much longer period still find a total amplitude likely to be less than 0.1 magnitudes, and the variation is considered to be irregular. [39]
The photosphere shows abundances of carbon, oxygen, and nitrogen that suggest the giant has gone through its first dredge-up stage—a normal step in the evolution of a star into a red giant during which material from deep within the star is brought up to the surface by convection. [40] With its slow rotation, Aldebaran lacks a dynamo needed to generate a corona and hence is not a source of hard X-ray emission. However, small scale magnetic fields may still be present in the lower atmosphere, resulting from convection turbulence near the surface. The measured strength of the magnetic field on Aldebaran is 0.22 Gauss. [41] Any resulting soft X-ray emissions from this region may be attenuated by the chromosphere, although ultraviolet emission has been detected in the spectrum. [42] The star is currently losing mass at a rate of (1–1.6) × 10 −11 M⊙ yr −1 (about one Earth mass in 300,000 years) with a velocity of 30 km s −1 . [40] This stellar wind may be generated by the weak magnetic fields in the lower atmosphere. [42]
Beyond the chromosphere of Aldebaran is an extended molecular outer atmosphere (MOLsphere) where the temperature is cool enough for molecules of gas to form. This region lies at about 2.5 times the radius of the star and has a temperature of about 1,500 K . The spectrum reveals lines of carbon monoxide, water, and titanium oxide. [40] Outside the MOLSphere, the stellar wind continues to expand until it reaches the termination shock boundary with the hot, ionized interstellar medium that dominates the Local Bubble, forming a roughly spherical astrosphere with a radius of around 1,000 AU, centered on Aldebaran. [43]
Five faint stars appear close to Aldebaran in the sky. These double star components were given upper-case Latin letter designations more or less in the order of their discovery, with the letter A reserved for the primary star. Some characteristics of these components, including their position relative to Aldebaran, are shown in the table.
| α Tau | Apparent Omvang | Angular Separation (″) | Position Angle (°) | Jaar | Parallax (mas) |
|---|---|---|---|---|---|
| B | 13.60 | 31.60 | 113 | 2007 | 47.3417 ± 0.1055 [44] |
| C | 11.30 | 129.50 | 32 | 2011 | 19.1267 ± 0.4274 [45] |
| D | 13.70 | — | — | — | — |
| E | 12.00 | 36.10 | 323 | 2000 | |
| F | 13.60 | 255.70 | 121 | 2000 | 0.1626 ± 0.0369 [46] |
Some surveys, for example Gaia Data Release 2, [44] have indicated that Alpha Tauri B may have about the same proper motion and parallax as Aldebaran and thus may be a physical binary system. These measurements are difficult, since the dim B component appears so close to the bright primary star, and the margin of error is too large to establish (or exclude) a physical relationship between the two. So far neither the B component, nor anything else, has been unambiguously shown to be physically associated with Aldebaran. [47] A spectral type of M2.5 has been published for Alpha Tauri B. [48]
Alpha Tauri CD is a binary system with the C and D component stars gravitationally bound to and co-orbiting each other. These co-orbiting stars have been shown to be located far beyond Aldebaran and are members of the Hyades star cluster. As with the rest of the stars in the cluster they do not physically interact with Aldebaran in any way. [31]
In 1993 radial velocity measurements of Aldebaran, Arcturus and Pollux showed that Aldebaran exhibited a long-period radial velocity oscillation, which could be interpreted as a substellar companion. The measurements for Aldebaran implied a companion with a minimum mass 11.4 times that of Jupiter in a 643-day orbit at a separation of 2.0 AU (300 Gm) in a mildly eccentric orbit. However, all three stars surveyed showed similar oscillations yielding similar companion masses, and the authors concluded that the variation was likely to be intrinsic to the star rather than due to the gravitational effect of a companion. [49]
In 2015 a study showed stable long-term evidence for both a planetary companion and stellar activity. [12] An asteroseismic analysis of the residuals to the planet fit has determined that Aldebaran b has a minimum mass of 5.8 ± 0.7 Jupiter masses, and that when the star was on the main sequence it would have given this planet Earth-like levels of illumination and therefore, potentially, temperature. [11] This would place it and any of its moons in the habitable zone.
Aldebaran was originally نير الضبران (Nā᾽ir al Dabarān in Arabic), meaning "the bright one of the follower". al Dabarān (الدبران) then applied to the whole of the lunar mansion containing the Hyades. [16] It is assumed that what it was following is the Pleiades. [15] A variety of transliterated spellings have been used, with the current Aldebaran becoming standard relatively recently. [16]
Mythology Edit
This easily seen and striking star in its suggestive asterism is a popular subject for ancient and modern myths.
- Mexican culture: For the Seris of northwestern Mexico, this star provides light for the seven women giving birth (Pleiades). It has three names: Hant Caalajc Ipápjö, Queeto, en Azoj Yeen oo Caap ("star that goes ahead"). The lunar month corresponding to October is called Queeto yaao "Aldebaran's path". [50]
- Aboriginal culture: in the Clarence River of northeastern New South Wales, this star is the Ancestor Karambal, who stole another man's wife. The woman's husband tracked him down and burned the tree in which he was hiding. It is believed that he rose to the sky as smoke and became the star Aldebaran. [51]
Names in other languages Edit
- In Hindu astronomy it is identified as the lunar mansion Rohini ("the red one") and as one of the twenty-seven daughters of Daksha and the wife of the god Chandra (Moon).
- In Ancient Greek it has been called Λαμπαδίας Lampadias, literally "torch-like of -bearer". [52]
- In Chinese, 畢宿 (Bì Xiù), betekenis Net, refers to an asterism consisting Aldebaran, ε Tauri, δ 3 Tauri, δ 1 Tauri, γ Tauri, 71 Tauri and λ Tauri. [53] Consequently, the Chinese name for Aldebaran itself is 畢宿五 (Bì Xiù wǔ), "the Fifth Star of Net". [54]
In modern culture Edit
The name Aldebaran or Alpha Tauri has been adopted many times, including
- in Antarctica
- United States Navy stores ship USS Aldebaran (AF-10) and Italian frigate Aldebaran (F 590)
- proposed micro-satellite launch vehicle Aldebaran
- French company Aldebaran Robotics
- fashion brand AlphaTauri team Scuderia AlphaTauri, previously known as Toro Rosso
The star also appears in works of fiction such as Far From the Madding Crowd en Down and Out in Paris and London. It is frequently seen in science fiction, including the Lensman series en Fallen Dragon. As the brightest star in a Zodiac constellation, it is also given great significance within astrology.
Aldebaran regularly features in conspiracy theories as one of the origins of extraterrestrial aliens, [55] often linked to Nazi UFOs. [56] A well-known example is the German conspiracy theorist Axel Stoll, who considered the star the home of the Aryan race and the target of expeditions by the Wehrmacht. [57]
The planetary exploration probe Pioneer 10 is no longer powered or in contact with Earth, but its trajectory is taking it in the general direction of Aldebaran. It is expected to make its closest approach in about two million years. [58]
29.1 The Age of the Universe
To explore the history of the universe, we will follow the same path that astronomers followed historically—beginning with studies of the nearby universe and then probing ever-more-distant objects and looking further back in time.
The realization that the universe changes with time came in the 1920s and 1930s when measurements of the redshifts of a large sample of galaxies became available. With hindsight, it is surprising that scientists were so shocked to discover that the universe is expanding. In fact, our theories of gravity demand that the universe must be either expanding or contracting. To show what we mean, let’s begin with a universe of finite size—say a giant ball of a thousand galaxies. All these galaxies attract each other because of their gravity. If they were initially stationary, they would inevitably begin to move closer together and eventually collide. They could avoid this collapse only if for some reason they happened to be moving away from each other at high speeds. In just the same way, only if a rocket is launched at high enough speed can it avoid falling back to Earth.
The problem of what happens in an infinite universe is harder to solve, but Einstein (and others) used his theory of general relativity (which we described in Black Holes and Curved Spacetime) to show that even infinite universes cannot be static. Since astronomers at that time did not yet know the universe was expanding (and Einstein himself was philosophically unwilling to accept a universe in motion), he changed his equations by introducing an arbitrary new term (we might call it a fudge factor) called the cosmological constant . This constant represented a hypothetical force of repulsion that could balance gravitational attraction on the largest scales and permit galaxies to remain at fixed distances from one another. That way, the universe could remain still.
About a decade later, Hubble, and his coworkers reported that the universe is expanding, so that no mysterious balancing force is needed. (We discussed this in the chapter on Galaxies.) Einstein is reported to have said that the introduction of the cosmological constant was “the biggest blunder of my life.” As we shall see later in this chapter, however, relatively recent observations indicate that the expansion is accelerating. Observations are now being carried out to determine whether this acceleration is consistent with a cosmological constant. In a way, it may turn out that Einstein was right after all.
Link to Learning
View this web exhibit on the history of our thinking about cosmology, with images and biographies, from the American Institute of Physics Center for the History of Physics.
The Hubble Time
If we had a movie of the expanding universe and ran the film backward, what would we see? The galaxies, instead of moving apart, would move together in our movie—getting closer and closer all the time. Eventually, we would find that all the matter we can see today was once concentrated in an infinitesimally small volume. Astronomers identify this time with the beginning of the universe. The explosion of that concentrated universe at the beginning of time is called the Big Bang (not a bad term, since you can’t have a bigger bang than one that creates the entire universe). But when did this bang occur?
We can make a reasonable estimate of the time since the universal expansion began. To see how astronomers do this, let’s begin with an analogy. Suppose your astronomy class decides to have a party (a kind of “Big Bang”) at someone’s home to celebrate the end of the semester. Unfortunately, everyone is celebrating with so much enthusiasm that the neighbors call the police, who arrive and send everyone away at the same moment. You get home at 2 a.m., still somewhat upset about the way the party ended, and realize you forgot to look at your watch to see what time the police got there. But you use a map to measure that the distance between the party and your house is 40 kilometers. And you also remember that you drove the whole trip at a steady speed of 80 kilometers/hour (since you were worried about the police cars following you). Therefore, the trip must have taken:
So the party must have broken up at 1:30 a.m.
No humans were around to look at their watches when the universe began, but we can use the same technique to estimate when the galaxies began moving away from each other. (Remember that, in reality, it is space that is expanding, not the galaxies that are moving through static space.) If we can measure how far apart the galaxies are now, and how fast they are moving, we can figure out how long a trip it’s been.
Let’s call the age of the universe measured in this way T0. Let’s first do a simple case by assuming that the expansion has been at a constant rate ever since the expansion of the universe began. In this case, the time it has taken a galaxy to move a distance, d, away from the Milky Way (remember that at the beginning the galaxies were all together in a very tiny volume) is (as in our example)
waar v is the velocity of the galaxy. If we can measure the speed with which galaxies are moving away, and also the distances between them, we can establish how long ago the expansion began.
Making such measurements should sound very familiar. This is just what Hubble and many astronomers after him needed to do in order to establish the Hubble law and the Hubble constant . We learned in Galaxies that a galaxy’s distance and its velocity in the expanding universe are related by
waar H is the Hubble constant. Combining these two expressions gives us
We see, then, that the work of calculating this time was already done for us when astronomers measured the Hubble constant. The age of the universe estimated in this way turns out to be just the reciprocal of the Hubble constant (that is, 1/H). This age estimate is sometimes called the Hubble time . For a Hubble constant of 20 kilometers/second per million light-years, the Hubble time is about 15 billion years. (By the way, the unit used by astronomers for the Hubble constant is kilometers/second per million parsecs. In these units, the Hubble constant is equal to about 70 kilometers/second per million parsecs, again with an uncertainty of about 5%.)
To make numbers easier to remember, we have done some rounding here. Estimates for the Hubble constant are actually closer to 21 or 22 kilometers/second per million light-years, which would make the age closer to 14 billion years. But there is still about a 5% uncertainty in the Hubble constant, which means the age of the universe estimated in this way is also uncertain by about 5%.
To put these uncertainties in perspective, however, you should know that 50 years ago, the uncertainty was a factor of 2. Remarkable progress toward pinning down the Hubble constant has been made in the last couple of decades.
The Role of Deceleration
The Hubble time is the right age for the universe only if the expansion rate has been constant throughout the time since the expansion of the universe began. Continuing with our end-of-the-semester-party analogy, this is equivalent to assuming that you traveled home from the party at a constant rate, when in fact this may not have been the case. At first, mad about having to leave, you may have driven fast, but then as you calmed down—and thought about police cars on the highway—you may have begun to slow down until you were driving at a more socially acceptable speed (such as 80 kilometers/hour). In this case, given that you were driving faster at the beginning, the trip home would have taken less than a half-hour.
In the same way, in calculating the Hubble time, we have assumed that the expansion rate has been constant throughout all of time. It turns out that this is not a good assumption. Earlier in their thinking about this, astronomers expected that the rate of expansion should be slowing down. We know that matter creates gravity, whereby all objects pull on all other objects. The mutual attraction between galaxies was expected to slow the expansion as time passed. This means that, if gravity were the only force acting (a big if, as we shall see in the next section), then the rate of expansion must have been faster in the past than it is today. In this case, we would say the universe has been decelerating since the beginning.
How much it has decelerated depends on the importance of gravity in slowing the expansion. If the universe were nearly empty, the role of gravity would be minor. Then the deceleration would be close to zero, and the universe would have been expanding at a constant rate. But in a universe with any significant density of matter, the pull of gravity means that the rate of expansion should be slower now than it used to be. If we use the current rate of expansion to estimate how long it took the galaxies to reach their current separations, we will overestimate the age of the universe—just as we may have overestimated the time it took for you to get home from the party.
A Universal Acceleration
Astronomers spent several decades looking for evidence that the expansion was decelerating, but they were not successful. What they needed were 1) larger telescopes so that they could measure the redshifts of more distant galaxies and 2) a very luminous standard bulb (or standard candle), that is, some astronomical object with known luminosity that produces an enormous amount of energy and can be observed at distances of a billion light-years or more.
Recall that we discussed standard bulb s in the chapter on Galaxies. If we compare how luminous a standard bulb is supposed to be and how dim it actually looks in our telescopes, the difference allows us to calculate its distance. The redshift of the galaxy such a bulb is in can tell us how fast it is moving in the universe. So we can measure its distance and motion independently.
These two requirements were finally met in the 1990s. Astronomers showed that supernovae of type Ia (see The Death of Stars), with some corrections based on the shapes of their light curves, are standard bulbs. This type of supernova occurs when a white dwarf accretes enough material from a companion star to exceed the Chandrasekhar limit and then collapses and explodes. At the time of maximum brightness, these dramatic supernovae can briefly outshine the galaxies that host them, and hence, they can be observed at very large distances. Large 8- to 10-meter telescopes can be used to obtain the spectra needed to measure the redshifts of the host galaxies (Figure 29.3).
The result of painstaking, careful study of these supernovae in a range of galaxies, carried out by two groups of researchers, was published in 1998. It was shocking—and so revolutionary that their discovery received the 2011 Nobel Prize in Physics. What the researchers found was that these type Ia supernovae in distant galaxies were fainter than expected from Hubble’s law, given the measured redshifts of their host galaxies. In other words, distances estimated from the supernovae used as standard bulbs disagreed with the distances measured from the redshifts.
If the universe were decelerating, we would expect the far-away supernovae to be helderder than expected. The slowing down would have kept them closer to us. Instead, they were fainter, which at first seemed to make no sense.
Before accepting this shocking development, astronomers first explored the possibility that the supernovae might not really be as useful as standard bulbs as they thought. Perhaps the supernovae appeared too faint because dust along our line of sight to them absorbed some of their light. Or perhaps the supernovae at large distances were for some reason intrinsically less luminous than nearby supernovae of type Ia.
A host of more detailed observations ruled out these possibilities. Scientists then had to consider the alternative that the distance estimated from the redshift was incorrect. Distances derived from redshifts assume that the Hubble constant has been truly constant for all time. We saw that one way it might not be constant is that the expansion is slowing down. But suppose neither assumption is right (steady speed or slowing down.)
Suppose, instead, that the universe is accelerating. If the universe is expanding faster now than it was billions of years ago, our motion away from the distant supernovae has sped up since the explosion occurred, sweeping us farther away from them. The light of the explosion has to travel a greater distance to reach us than if the expansion rate were constant. The farther the light travels, the fainter it appears. This conclusion would explain the supernova observations in a natural way, and this has now been substantiated by many additional observations over the last couple of decades. It really seems that the expansion of the universe is accelerating, a notion so unexpected that astronomers at first resisted considering it.
How can the expansion of the universe be speeding up? If you want to accelerate your car, you must supply energy by stepping on the gas. Similarly, energy must be supplied to accelerate the expansion of the universe. The discovery of the acceleration was shocking because scientists still have no idea what the source of the energy is. Scientists call whatever it is dark energy , which is a clear sign of how little we understand it.
Note that this new component of the universe is not the dark matter we talked about in earlier chapters. Dark energy is something else that we have also not yet detected in our laboratories on Earth.
What is dark energy? One possibility is that it is the cosmological constant, which is an energy associated with the vacuum of “empty” space itself. Quantum mechanics (the intriguing theory of how things behave at the atomic and subatomic levels) tells us that the source of this vacuum energy might be tiny elementary particles that flicker in and out of existence everywhere throughout the universe. Various attempts have been made to calculate how big the effects of this vacuum energy should be, but so far these attempts have been unsuccessful. In fact, the order of magnitude of theoretical estimates of the vacuum energy based on the quantum mechanics of matter and the value required to account for the acceleration of the expansion of the universe differ by an incredible factor of at least 10 120 (that is a 1 followed by 120 zeros)! Various other theories have been suggested, but the bottom line is that, although there is compelling evidence that dark energy exists, we do not yet know the source of that energy.
Whatever the dark energy turns out to be, we should note that the discovery that the rate of expansion has not been constant since the beginning of the universe complicates the calculation of the age of the universe. Interestingly, the acceleration seems not to have started with the Big Bang. During the first several billion years after the Big Bang, when galaxies were close together, gravity was strong enough to slow the expansion. As galaxies moved farther apart, the effect of gravity weakened. Several billion years after the Big Bang, dark energy took over, and the expansion began to accelerate (Figure 29.4).
Deceleration works to make the age of the universe estimated by the simple relation T0 = 1/H seem older than it really is, whereas acceleration works to make it seem younger. By happy coincidence, our best estimates of how much deceleration and acceleration occurred lead to an answer for the age very close to T0 = 1/H . The best current estimate is that the universe is 13.8 billion years old with an uncertainty of only about 100 million years.
Throughout this chapter, we have referred to the Hubble constant. We now know that the Hubble constant does change with time. It is, however, constant everywhere in the universe at any given time. When we say the Hubble constant is about 70 kilometers/second/million parsecs, we mean that this is the value of the Hubble constant at the current time.
Comparing Ages
We now have one estimate for the age of the universe from its expansion. Is this estimate consistent with other observations? For example, are the oldest stars or other astronomical objects younger than 13.8 billion years? After all, the universe has to be at least as old as the oldest objects in it.
In our Galaxy and others, the oldest stars are found in the globular clusters (Figure 29.5), which can be dated using the models of stellar evolution described in the chapter Stars from Adolescence to Old Age.
The accuracy of the age estimates of the globular clusters has improved markedly in recent years for two reasons. First, models of interiors of globular cluster stars have been improved, mainly through better information about how atoms absorb radiation as they make their way from the center of a star out into space. Second, observations from satellites have improved the accuracy of our measurements of the distances to these clusters. The conclusion is that the oldest stars formed about 12–13 billion years ago.
This age estimate has recently been confirmed by the study of the spectrum of uranium in the stars. The isotope uranium-238 is radioactive and decays (changes into another element) over time. (Uranium-238 gets its designation because it has 92 protons and 146 neutrons.) We know (from how stars and supernovae make elements) how much uranium-238 is generally made compared to other elements. Suppose we measure the amount of uranium relative to nonradioactive elements in a very old star and in our own Sun, and compare the abundances. With those pieces of information, we can estimate how much longer the uranium has been decaying in the very old star because we know from our own Sun how much uranium decays in 4.5 billion years.
The line of uranium is very weak and hard to make out even in the Sun, but it has now been measured in one extremely old star using the European Very Large Telescope (Figure 29.6). Comparing the abundance with that in the solar system, whose age we know, astronomers estimate the star is 12.5 billion years old, with an uncertainty of about 3 billion years. While the uncertainty is large, this work is important confirmation of the ages estimated by studies of the globular cluster stars. Note that the uranium age estimate is completely independent it does not depend on either the measurement of distances or on models of the interiors of stars.
As we shall see later in this chapter, the globular cluster stars probably did not form until the expansion of the universe had been underway for at least a few hundred million years. Accordingly, their ages are consistent with the 13.8 billion-year age estimated from the expansion rate.
Activities
Determining the position of a star or other object in space is an important concept in astronomy. During this activity you will learn how the distances to nearby stars can be measured using the parallax effect, and put this method into practise to determine the distance to nearby stars.
Star in a Box (Paper-based)
Have you ever wondered what happens to stars as they get older? Explore the evolution of stars with different masses.
Star in a Box
Have you ever wondered what happens to the different stars in the night sky as they get older? This activity lets you explore the life-cycle of stars.
Return to Earth: Build a Lander
Students will work in groups to design, test and build a model lander to safely transport their “astronaut” to Earth. This activity will provide your class with an exciting context within which to explore the effects of gravity, air resistance and friction on movement.
Preparing an Observation Request on LCO
Students will carry out an observing session on the LCO robotic telescope network, using astronomical catalogues and planetarium software to determine target objects suitable for observation with the instruments available, within the allotted time window. Students will select appropriate observation parameters including filters and exposure times.
Plotting a Supernova Light curve
A supernova is the explosive death of a massive star. Although they only burn for a short amount of time, supernovae can tell us a lot about the Universe, including how to measure distance in space. In this activity you will plot the changing brightness of the object and interpret your data to study how these objects evolve.
Plotting an Asteroid Light Curve
One of the things we hope to learn through observation of near-Earth objects is their exact rotation rate. We can do by taking a series of observations of the object over time, and plotting the change in brightness. Using Asteroid Tracker you can help collect observations of interesting NEO targets, then plot and interpret your data to measure the rotation period of an asteroid.
Play Bingo with Charles Messier
Play a game of bingo and learn about the many wonders of the cosmos!
Measuring the Age of the Universe
The discovery of the expanding Universe was one of the greatest revelations in astronomy. During this activity students will relive Hubble’s monumental discovery by using real supernova spectra to create a famous Hubble Diagram.
Measure the diameter of the Sun
In this activity you will measure how fast the Sun moves to caclulate how big the Sun appears in the sky. All you need are some household items and about 20 minutes on a sunny day.
Measure the Age of Ancient Cosmic Explosions
In this project you will calculate the age of a supernova remnant using Las Cumbres Observatory and Hubble Space Telescope observations. You will compare the remnant's radius in images taken several years apart to determine the expansion velocity and use this to calculate how long ago the supernova explosion occurred.
How to Find Images Using the LCO Science Archive
There are many thousands of astronomical data files in our archive. We've created an archive search page that lets you limit your search by different attributes. This guide will walk you through the steps to finding the images you want.
How to Create Stunning Colour Images of the Cosmos (Using Pixlr)
This guide will show you how to create beautiful colour images using free online software.
How to Create Stunning Colour Images of the Cosmos (Using Photoshop)
This article will tell you how to use Adobe Photoshop to make high quality color images with your astronomical data.
How to Create Stunning Colour Images of the Cosmos (Using GIMP)
This guide will show you how to create beautiful colour images using free software that can be downloaded from the Internet.
How Big is the Solar System?
How long would it take to travel to the Moon? Could you travel to the edge of the Solar System and beyond? In this activity students learn about the size of the Solar System, beginning with the Earth and Moon and reaching out to encompass the entire Solar System.
Down2Earth: Making Impact Craters
The aim of this activity is to understand the effect the mass and velocity of an impacting object has on the resulting crater, in terms of diameter, depth and ejecta rays and relate this information to the craters on the surfaces of Earth and the Moon.
Create a Hubble Tuning Fork diagram
In this activity you will create stunning colour images of galaxies and add them to the Tuning Fork template to recreate the famous Hubble image.
Craters in the classroom
After carrying out this activity, students will understand the effect the mass, velocity and angle of an impacting object has on the resulting crater, in terms of diameter, depth and ejecta rays, and relate this information to the craters on the surfaces of Earth and the Moon.
Calculating the Age of Solar System Objects
How old are the objects within our Solar System? One method scientists use to answer this important question is counting the number of craters on their surface. This information, combined with the time it takes for craters to form on each body, gives us a strong estimate how old the object is. In this activity students will put this method into practise to calculate the age of five bodies within our Solar System.
Astronomical Seeing - How Good are the Observing Conditions?
Have you ever wondered why you see the stars in the night sky more clearly on some nights than on others? You are about to measure quantitatively how the Earth’s atmosphere affects the quality of sky images, and thereby imposes fundamental limitations to ground-based astronomical observations.
Astronaut Training: Taste
There are no refrigerators or ovens on the International Space Station, but that isn’t the only reason that eating can be a strange experience for astronauts. Due to lack of gravity and shifting fluids, things can taste very different in space. In this activity students will carry out a taste test to explore how our senses affect the flavour of our food, and what this might reveal about eating in space.
Astronaut Training: Dexterity
Working in teams, students must complete a jigsaw puzzle and reveal the hidden word as quickly as possible, while their dexterity is impaired, to simulate the difficulties faced by astronauts when attempting to fix satellites and instruments wearing bulky spacesuits. Assembling a puzzle quickly and correctly will help them understand the importance of dexterity, hand-eye coordination and communication -- essential skills for an astronaut!
Agent Exoplanet
Use the Agent Exoplanet interface to measure changes in the brightness of a star as an orbiting exoplanet transits. Contribute measurements to the Agent Exoplanet community. Describe an exoplanet light curve and its relationship to the physical process causing it.
How Do We Know How Old Everything Is?
I know it’s impolite to ask, but, how old are you? And how do you know? And doesn’t comparing your drivers license to your beautiful and informative “Year In Space” calendar feel somewhat arbitrary? How do we know old how everything is when what we observe was around long before calendars, or the Earth, or even the stars?
Scientists have pondered about the age of things since the beginning of science. When did that rock formation appear? When did that dinosaur die? How long has the Earth been around? When did the Moon form? What about the Universe? How long has that party been going on? Can I drink this beer yet, or will I go blind? How long can Spam remain edible past its expiration date?
As with distance, scientists have developed a range of tools to measure the age of stuff in the Universe. From rocks, to stars, to the Universe itself. Just like distance, it works like a ladder, where certain tools work for the youngest objects, and other tools take over for middle aged stuff, and other tools help to date the most ancient.
Let’s start with the things you can actually get your hands on, like plants, rocks, dinosaur bones and meteorites. Scientists use a technique known as radiometric dating. The nuclear age taught us how to blow up stuff real good, but it also helped understand how elements transform from one element to another through radioactive decay.
For example, there’s a version of carbon, called carbon-14. If you started with a kilo of it, after about 5,730 years, half of it would have turned into carbon-12. And then by 5,730 more years, you’d have about ¼ carbon-14 and ¾ carbon-12.
This is known as an element’s half-life. And so, if you measure the ratio of carbon-12 to carbon-14 in a dead tree, for example, you can calculate how long ago it lived. Different elements work for different ages. Carbon-14 works for the last 50,000 years or so, while Uranium-238 has a half-life of 4.5 billion years, and will let you date the most ancient of rocks. But what about the stuff we can’t touch, like stars?
When you use a telescope to view a star, you can break up its light into different colors, like a rainbow. This is known as a star’s spectra, and if you look carefully, you can see black lines, or gaps, which correspond to certain elements. Since they can measure the ratios of different elements, astronomers can just look at a star to see how old it is. They can measure the ratio of uranium-238 to lead-206, and know how long that star has been around. How astronomers know the age of the Universe itself is one of my favorites, and we did a whole episode on this.
Artist’s conception of Planck, a space observatory operated by the European Space Agency, and the cosmic microwave background. Credit: ESA and the Planck Collaboration – D. Ducros
The short answer is, they measure the wavelength of the Cosmic Microwave Background Radiation. Since they know this used to be visible light, and has been stretched out by the expansion of the Universe, they can extrapolate back from its current wavelength to what it was at the beginning of the Universe. This tells them the age is about 13.8 billion years. Radiometric dating was a revolution for science. It finally gave us a dependable method to calculate the age of anything and everything, and finally figure out how long everything has been around.
