Sterrekunde

Watter breuk materie is nie gebind aan die sterrestelsels, groepe en trosse wat ons sien nie?

Watter breuk materie is nie gebind aan die sterrestelsels, groepe en trosse wat ons sien nie?


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Ons weet dat die meeste materie in die heelal in sterrestelsels en sterrestelsels in groepe en trosse ineengestort het, en dat baie materie tans in trosse tussen die sterrestelsels is. Maar watter fraksie van die totale materie word nie deur hierdie diskrete waargenome entiteite voorgestel nie? Sommige donker materie kan snelhede te hoog hê om in stralekrans te val, miskien deur getysterte wat uit samesmeltings ontsnap. Daar moet 'n relikwie medium in holtes wees met 'n digtheid wat te laag is om sterrestelsels te vorm. Sommige stralekrans is dalk te klein om sterre te vorm. Kom dit alles by tot 'n beduidende intergalaktiese medium (IGM)? Gee n-liggaamsimulasies 'n nommer hiervoor?

'N Mens sou dink dat ons die antwoord op hierdie vraag kon kry deur al die bekende massa in die nabygeleë heelal bymekaar te tel en af ​​te trek van die afgeleide gemiddelde digtheid van die heelal maal die volume wat gebruik is. Sommige onlangse waarnemingstudies dui daarop dat die plaaslike digtheid ver onder die gemiddelde digtheid is en dat dit die oorsaak is van die Hubble konstante verskil.


Universiteit van Kalifornië, San Diego Sentrum vir Astrofisika en ruimtewetenskappe

Sterrestelsels word geklassifiseer volgens hul eienskappe rykheid (aantal lede), vorm (bolvormig, afgeplat of onreëlmatig) en galaktiese inhoud (spiraalryk, spiraalarm of ellipties). Sommige is sterk radiobronne, terwyl ander x-strale uitstraal. Die rykste nabygeleë groep is Maagd, 60 miljoen ligjare van die Melkweg af. Dit bevat ongeveer 2500 sterrestelsels, meestal elliptiese.
Die plaaslike groep sterrestelsels

Ons woon in 'n klein groepie genaamd die Local Group, wat oorheers word deur twee reuse-spiraalstelsels, Andromeda en ons eie Melkweg. Benewens Messier 33, 'n tussentydse massa-Sc-sterrestelsel, is daar 15 elliptiese en 13 onreëlmatige sterrestelsels in die groep, waaronder die Magellaniese wolke, ons Melkweg se satelliete, Messier 32 en NGC 205, satelliete van Andromeda. Die groep het 'n grootte van ongeveer 3 miljoen l.y., en het 'n totale massa van 5 x 10 12 M

Die Virgo Cluster, ongeveer 50 miljoen l.y. weg, is die naaste gereelde sterrestelsel met 'n paar honderde lede. Ons plaaslike groep is 'n afgeleë lid van 'n 'supercluster' sterrestelsels waarvan die Maagd-groep die dominante lid is.

Die Hubble-ruimteteleskoop het die eerste geleentheid gebied om terug te kyk na die vroeë heelal by trosse. Miljarde jare gelede bevat trosse baie meer spiraalvormige sterrestelsels as wat dit vandag is. Hulle is waarskynlik met verloop van tyd ontwrig deur botsings en samesmeltings binne die groepe.

CL 0024 + 1654 is 'n groot groep sterrestelsels wat 5 miljard ligjaar van die aarde af geleë is. Dit is kenmerkend vanweë sy rykdom (groot aantal sterrestelsels), en sy wonderlike swaartekraglens. Die blou lusse op die voorgrond is lensbeelde van 'n spiraalagtige sterrestelsel wat agter die tros geleë is.

  • Kyk hoe wissel die groepmassa die snelhede van die sterrestelsels.
  • Cluster Atlas van die Universiteit van Alabama
  • Vaar deur die Maagdekluster vanaf die Limber Observatory.
  • APOD se Galaxy Cluster Links.

Einstein se Algemene Relatiwiteitsteorie toon aan dat 'n groot massa die ruimtetyd kan vervorm en die pad van die lig kan buig. Dus, 'n baie massiewe voorwerp, soos 'n groep sterrestelsels, kan as 'n swaartekraglens dien. Wanneer lig deur die groep gaan van 'n voorwerp wat daaragter lê, word die lig gebuig en gefokus om 'n beeld of beelde van die bron te lewer. Die beeld kan vergroot, verdraai word of met die lens vermenigvuldig word, afhangende van die posisie van die bron ten opsigte van die lesmassa.


Skematiese diagram van 'n sterrestelsel wat as 'n swaartekraglens optree


Die kenmerke van die gravitasie-lensbeeld hang af van die belyning van die waarnemer, die lens en die agtergrondvoorwerp. As die belyning perfek is, is die resulterende beeld 'n Einstein-ring, links getoon. Hierdie voorwerp, ontdek deur radio-sterrekundiges in die Engelse Jodrell Bank Radio Observatory, wat dan in die nabye infrarooi met HST afgebeeld is, is waarskynlik 'n verre agtergrondstelsel wat deur 'n tussenafstand Elliptiese sterrestelsel gelees word, getoon as die helder beeld in die middel van die ring. Die ring is na raming ongeveer 10-20 keer helderder as wat die sterrestelsel op die agtergrond sonder lens sou voorkom.

As die belyning nie perfek is nie, word veelvuldige beelde eerder as 'n ring gevorm. Die voorwerp aan die regterkant, genaamd die Einstein-kruis, toon vier beelde van 'n verre kwasar by 'n rooi verskuiwing, z = 1.7, afgebeeld deur 'n tussenliggende spiraalagtige sterrestelsel met z = 0,04. HST-beelde is verwerk om die sterrestelsel- en kwasarbeelde te skei.

A swaartekraglens is die doeltreffendste as dit naby die middel tussen die waarnemer en die voorwerp wat ver lens word, is. Die versterking, die verhouding tussen die helderheid van die lens van 'n voorwerp en die waarde van die lens, is groter as die siglyn baie naby die lens beweeg. Lense kan die helderheid 'n paar keer versterk, tot meer as 'n faktor van 100 - dit beteken dat lense die potensiaal bied om voorwerpe 10 keer verder weg te "sien".


Mikrolensering van 'n ster in die LMC deur 'n voorwerp in die Melkweg, vanuit die MACHO-projek

  1. Sterre / oorblyfsels / bruin dwerge / planete - As 'n voorwerp in die melkweg tussen ons en 'n verre ster inbeweeg, sal dit die lig van die agtergrondster fokus en versterk soos aangedui in die ligkromme hierbo. Verskeie gebeurtenisse van hierdie tipe is waargeneem in die Groot Magellaanse Wolk, 'n klein sterrestelsel naby ons Melkweg. MACHO-projek
  2. Sterrestelsels - Massiewe sterrestelsels kan ook as swaartekraglense dien. Lig van 'n bron wat agter die sterrestelsel lê, is gebuig en gefokus om 'n beeld of beelde van die bron te skep. Omdat die massa in 'n sterrestelsel nie eweredig versprei word nie, word die beelde dikwels vervorm of vergroot.
  3. Clusters of Galaxies - Soos hierbo getoon vir CL 0024 + 1654, kan 'n massiewe groep verskeie beelde skep van 'n ver voorwerp wat daaragter lê. Met swaartekraglense kan ons voorwerpe waarneem wat te ver of te flou is om direk gesien te word. Aangesien na groter afstande gekyk word, beteken dit dat u verder in die tyd moet kyk, kry ons toegang tot inligting oor die vroeë heelal.

Waarnemings van trosse en hul sterrestelsels het een van die belangrikste raaisels in die sterrekunde van vandag ontdek. Dit lyk asof trosse baie stabiel is; hulle bevat volwasse sterrestelsels met ou sterre, en dit lyk asof hulle miljarde jare gelede gevorm is. Maar as ons die hoeveelheid massa in 'n groep bereken met behulp van die wentelbewegings van sy sterrestelsels, is die resultaat te laag sodat die groep swaartekrag kan bind. As die groep slegs die massa bevat wat ons kan waarneem, is die gravitasiekrag onvoldoende om te voorkom dat die sterrestelsels "ontsnap". Daar moet meer massa in die groep wees as wat ons sien.


Rotasiekurwes vir 3 spiraalvormige sterrestelsels - sterrestelselbeeld (links), spektrum (middel - fotografiese negatief), en amp-plot (regs).
Die vlakheid van die rotasiekurwe sonder afwaartse draai dui aan dat die massaverdeling veel verder strek
die gemete waardes, waarskynlik in die vorm van 'n massiewe glans van donker materie.

Dieselfde probleem ontstaan ​​as ons na die sterrestelsels self kyk. Die rotasiekurwe van 'n sterrestelsel toon aan hoe die wentelsnelhede van die sterre verander met die afstand vanaf die middelpunt. As die sterrestelsel as 'n vaste skyf draai, sal die snelheid lineêr toeneem met afstand. As die grootste deel van die massa in die middel gekonsentreer is, soos in ons sonnestelsel, sal die snelhede van die sterre afneem met die vierkantswortel van die afstand. Maar dit is nie wat waargeneem word nie. Verby die punt waar geen massa sigbaar is nie, is die draai kurwes plat! Dit beteken dat die massa steeds toeneem namate ons na buite beweeg, alhoewel ons niks kan sien nie! Weereens moet ons 'donker saak' aanroep. Die sterrestelsel moet baie verder uitstrek as wat die ligstof aandui. In werklikheid vereis die berekeninge dat daar ten minste tien keer meer massa is as wat ons kan sien! Berekenings dui daarop dat hierdie donker materie waarskynlik in 'n uitgebreide stralekrans van donker materie sal wees.

Die aard van hierdie donker materie of 'ontbrekende massa' is onbekend. Daar is teorieë wat wissel van die bizzare tot die alledaagse, en geen van hulle beantwoord al die vrae suksesvol nie.

    Moontlike vorms van "Normale" (Baryoniese) saak
      Planete / bruin dwerge / sterreste (swart gate, neutronsterre en wit dwerge)

    • Planete - maar die massa planete is 'n klein fraksie van die massa van die Sonnestelsel. Is daar vrylopende planete soos Jupiter daar buite?
    • Bruin dwerge - tot 0,085 miljoen neem die aantal sterre dramaties toe as jy na sterre met 'n laer massa gaan. Gaan hierdie tendens voort terwyl ons onder die afsnypunt vir die ontbranding van kernreaksies gaan? As dit die geval is, word mislukte sterre genoem Bruin dwerge, kan 'n beduidende fraksie van die Dark Matter uitmaak. Bruin dwerge is moeilik om raak te sien, aangesien dit koel is en baie helder is. Onlangse infrarooi-studies het bruin dwerge gevind, maar nie in voldoende getalle om die donker materie wat in die melkweg benodig word, op te maak nie.
    • Sterreste - Dooie sterre, in die vorm van wit dwerge, neutronsterre of swart gate, kan die Donker Materie vorm, maar ons begrip van die geskiedenis van die Melkweg maak dit onwaarskynlik dat sterre voldoende vinnig in die verby om die nodige massa van 10 of meer keer die huidige massa sterre uit te maak.

    Miskien het sterrestelsels groot hoeveelhede gas wat nie verreken is nie. Maar koel atoomwaterstof sal radiogolwe van 21 cm uitstraal, en dit word nie gesien nie. Molekulêre waterstof moet sigbaar wees deur die ultravioletvrystelling daarvan, maar dit word nie waargeneem nie. Warm gas straal röntgenstrale uit, en verskeie sterrestelselgroepe is sterk röntgenbronne. Die massa intergalaktiese gas word bereken as 'n aansienlike hoeveelheid, miskien groter as die hoeveelheid in sterrestelsels en sterre, maar is steeds te min om die trosstabiliteit te verreken.

    Volgens die algemeen aanvaarde teorie, Big Bang Nucleosynthesis, het gewone atoomkerne gevorm soos die heelal uitgebrei en afgekoel het. Die teorie laat gedetailleerde berekeninge toe van die hoeveelheid helium (4 He) wat geproduseer word (ook 2 H - deuterium, 3 He, 4 Li, 4 Be, 4 B) wat teenwoordig moet wees, en dit is bevestig deur waarnemings. Die teorie stem egter net saam met waarneming as die totale hoeveelheid barione (protone en amp neutrone) beperk word. Daar is genoeg barione om donker materie te verreken, maar nie genoeg om die probleem op te los nie.

    • The Dark Matter Universe van die Universiteit van Oregon
    • Regtig mooi DM-tutoriaal van Jon Dursi @ Queens Univ. CA.
    • Berkeley Sentrum vir deeltjie-astrofisika Handleiding vir donker materie
    • Melkwegrotasiekurwes
    • Kandidate vir donker sake

    Gamma-Ray Bursts blyk een van die mees ontploffende nuwe gebiede van astronomiese navorsing te wees. Gamma-uitbarstings is in 1967 ontdek deur die Vela Satellites wat begin is om die nakoming van die Nuclear Test-Ban-verdrag van 1963 te monitor deur gammastralings op te spoor uit atmosferiese kerntoetse. Gelukkig is vinnig vasgestel dat die uitbarstings van buite-aardse oorsprong is (nee, nie ET nie!) Eerder as dat een of ander skelm staat kernoorlog begin. Aanvanklik was die aantal uitbarstings te klein en die vermoë om die uitbarstings vas te stel om te bepaal wat hul oorsprong is.


    Gamma-straaluitbarsting waargeneem deur BATSE
    In 1991 het die Compton Gamma-Ray Observatory sy Burst and Transient Source Experiment (BATSE) uitgevoer, gebou met deelname deur UCSD se hoë-energie astrofisici. in 'n wentelbaan. Die gammastraal bars van 'n paar sekondes tot 'n paar minute en is tot onlangs nog nie op ander golflengtes bespeur nie. BATSE het 'n paar duisend sarsies waargeneem en vasgestel dat dit eenvormig oor die lug versprei is.


    Optiese 'Afterglow' van 'n Gamma Ray Burst in a Galaxy, geskat op ongeveer 2 Miljoen ligjare weg.

    • UCSD se Gamma-Ray Burst Page.
    • Wetenskaplike Amerikaanse artikel
    • APOD se Gamma-Ray Burst Pages. van die Emory Universiteit.
    • Goddard Space Flight Center se Advanced & amp Elementary GRB Tutorials

    Prof. E. (Gene) Smith
    DASS 0424 UCSD
    9500 Gilmanrylaan
    La Jolla, CA 92093-0424


    Laaste opdatering: 29 Januarie 2000


    Kosmologie met behulp van Galaxy Clusters

    Die basiese eienskappe van die heelal beïnvloed hoe trosse gedurende hul leeftyd vorm en groei. Hierdie eienskappe sluit in die uitbreidingsnelheid van die heelal (H0), die fraksie van die heelal wat materie eerder as donker is (Ωm), die sterkte van 'n misterieuse afweermag bekend as donker energie (ΩΛ) en die sterkte van die groei van skommelinge (σ8). Daarom kan ons die eienskappe van die heelal meet (kosmologie doen) deur trosse te bestudeer.

    Aantal trosse as 'n funksie van rooiverskuiwing en massa wat deur eROSITA voorspel word (Merloni et al.)

    Die primêre manier om dit te doen, is om te tel hoeveel trosse daar van 'n bepaalde massa is as 'n funksie van die afstand van ons af. As ons verder wegkyk met teleskope, kyk ons ​​ook na die verlede van die heelal, want lig neem tyd om ons te bereik. Daarom, deur trosse met spesifieke massa-reekse te tel en te kyk hoe dit die 3-d grootskaalse struktuur vorm, bestudeer ons hoe trosse groei en ontwikkel gedurende die leeftyd van die heelal.

    Die HE-groep by MPE neem 'n leidende rol in die konstruksie van die eROSITA-instrument op die Russiese Spectrum-Roentgen-Gamma & quot (SRG) -satelliet, wat in 2016 van stapel gestuur sal word. Dit sal verskeie opnames van die lug in die X-straal doen. band, wat ons toelaat om tussen 50 en 100 duisend sterrestelsels te ontdek, benewens baie ander sterrekundige voorwerpe. Groot spektroskopiese en beeldopnames sal die X-straalwaarnemings aanvul. Analises van die optiese lig wat uitgestraal word deur die 100-1000 sterrestelsels wat hulle aanbied, sal die opname aanvul deur die afstand van die voorwerpe en die tydperk waarin dit waargeneem word, te bepaal. Ons sal hierdie groot aantal trosse gebruik om streng beperkings op die kosmologiese eienskappe van die heelal te lewer.


    1). Hulle het dinamiese tydskale wat 'n beduidende fraksie van die ouderdom van die heelal is, sodat ons kan sien hoe hulle ontwikkel oor selfs beskeie rooi verskuiwings. Dinamiese tydskale vir trosse is lank, dus is die afdruk van die aanvanklike toestande nog nie heeltemal uitgewis nie. Die groepmassaspektrum is sensitief vir die normalisering en helling van die kragspektrum op trosskale en is een van die sterkste toetse van kosmologiese modelle. Die massas en skale van trosse is van so 'n aard dat dit 'n regverdige steekproef van die massa van die heelal moet bevat met verteenwoordigende breuke van die verskillende komponente. Aangesien trosvorming deur gravitasie-ineenstorting redelik goed verstaan ​​word, kan vergelykings van trosseienskappe met teoretiese voorspellings vir verskillende kosmologiese modelle gebruik word om tussen hierdie modelle te onderskei. Ten slotte bied trosse belangrike inligting oor die oorsprong en oorvloed evolusie van swaar elemente in die heelal.

    Hoë rooiverskuiwingsgroepe

    Bykomende beperkings op kosmologiese modelle kan verkry word deur hoër rooiverskuiwingsgroepe te waarneem. Donahue en medewerkers (Donahue et al. 1998 ApJ, in pers Voit & Donahue 1998 ApJ, in pers sien ook Tucker et al. 1998 ApJ, in pers) het ASCA-waarnemings van z gebruik

    0,8 trosse om aan te toon dat hul temperature baie hoër is as wat verwag is in 'n Omega = 1, Lambda = 0-heelal.

    Daar word ook voortgegaan met die bepaling van H_0 vanuit ASCA en ROSAT X-straalwaarnemings. Om die gemete waardes van die clustergastemperatuur en die elektrongetaldigtheid te kombineer met radiowaarnemings van die Sunyaev-Zel'dovich-effek (die afname in die radiovloei wat lei tot kosmiese mikrogolf-agtergrondfotone wat deur die warm plasma van 'n groep beweeg en verskuif word na hoër energie) lewer 'n direkte maatstaf van H_0 aan die trosse wat bestudeer word. Hughes & Birkinshaw (1998 ApJ, in pers) met behulp van 'n steekproef van 8 trosse, vind 'n H_0 van 42 - 61 km / s / Mpc met 'n addisionele lukrake fout van 16%.

    Temperatuurkaarte

    ASCA-waarnemings van sterrestelsels word nou gebruik om die temperatuur van die warm intraklustermedium in kaart te bring. Hierdie waarnemings toon beduidende afwykings van isotermiteit in 'n groot aantal trosse. Hierdie waarnemings definieer die grootte van die verkoelingskerne wat in sommige trosse gesien word en illustreer die gevolge van skokke, blykbaar as gevolg van onlangse samesmeltings. Met temperatuurkaarte kan skokke en ander samesmeltingsverskynsels opgespoor word lank nadat die helderheid van die X-straaloppervlakte weer na azimutale simmetrie teruggekeer het (Churazov et al. 1998 ApJ, in pers Donnelly et al. 1998a, b ApJ, in pers en ingedien). ASCA-temperatuurkaarte vir ongeveer die helfte van alle groepe toon samesmeltingsskokke. In die A3266-groep is die optiese morfologie in ooreenstemming met 'n dreigende samesmelting van die NO of 'n onlangse samesmelting van die SW. Die ASCA-spektro-ruimtelike kaart toon kompressie en skokverhitting van die gas loodreg op die samesmeltingsas wat van die hoofgroep na die SW loop, wat die hipotese na die samesmelting uniek bevoordeel (Henriksen & Donnelly 1998, in voorbereiding). ASCA-waarnemings van A754 is gebruik om 'n gedetailleerde model van 'n samesmelting op te stel en die hoeveelheid meng van die samesmeltende komponente en die gevolglike nie-termiese drukondersteuning in die sentrale streke van die groep te skat (Roettiger et al. 1998 ApJ 493, 62).

    Figuur 1: Temperatuurkaart van die cluster fusie Abell 754 (Henriksen & Markevitch 1996 ApJ 466, L79).

    Markevitch et al. (1998, ApJ in pers en verwysings daarin), het die ASCA ruimtelik opgeloste spektroskopiese waarnemings vir 'n monster van 30 helder, nabygeleë trosse ontleed en hul geprojekteerde gastemperatuurprofiele afgelei, en op 'n growwe ruimtelike skaal, hul tweedimensionele temperatuurkaarte. Daar is gevind dat alle trosse nie-termies is, met ruimtelike temperatuurvariasies (afgesien van verkoelingsvloei) met 'n faktor van 1,3-2. Byna alle trosse toon 'n beduidende afname in radiale temperatuur in groot radiusse. Hierdie daling stem ooreen met die totale massa binne 1 en binne 6 kernstrale wat onderskeidelik ongeveer 1,35 en 0,7 keer die isotermiese beta-modelberamings is. Dus is die gasfraksie by groot radiuse groter as wat geskat is onder die aanname van isotermiteit. Hierdie resultaat versterk die argument vir 'n lae-Omega_0-kosmologie, gebaseer op die hoë barionfraksie in trosse. Dit impliseer ook 'n sterk skeiding van gas en donker materie, wat moontlik aandui dat ander bronne as swaartekrag 'n beduidende fraksie van die gas se termiese energie geproduseer het. Die daling in temperatuur met radius is steiler as wat voorspel word deur gepubliseerde hidrodinamiese simulasies.

    ASCA ruimtelik opgeloste analise het vir die eerste keer 'n direkte uitsluiting van die afkoelvloeistreke van die gemiddelde meting van die klustertemperatuur moontlik gemaak. Sodanige uitsluiting (Markevitch 1998 ApJ in pers Allen & Fabian MNRAS, in pers) verminder die verspreiding in die L_X-T en L_bol-T verhoudings aansienlik. Hierdie verhoudings is belangrike eienskappe wat afhanklik is van kosmologie en die termiese termiese geskiedenis. Die nuwe, verkoeling vloei-gekorrigeerde clustertemperature is gebruik om 'n meer akkurate clustertemperatuurfunksie by lae rooi verskuiwings te verkry (Markevitch 1998 ApJ, in pers). Dit is selfs meer afwykend van die standaard voorspellings van Cold Dark Matter as die vorige berekeninge.

    ASCA-waarnemings is belangrik om die evolusie van sterrestelsels met die evolusie van die groep self te korreleer. Henriksen & Wang (1998 MNRAS, ingedien) rapporteer resultate van 'n X-straalstudie van die sterrestelsel Abell 2111 (z = 0.23) wat toon dat hierdie klassieke Butcher-Oemler-tros langwerpig en asimmetries is, met klontjies op boogskale. Dit het ook 'n warm kern en het waarskynlik onlangs 'n samesmelting ondergaan, wat ook verantwoordelik kan wees vir die hoë fraksie blou sterrestelsels wat in die groep gesien word.

    Ruimtelik opgeloste temperatuurmetings is ook gebruik om die vorm van die swaartekragpotensiaal in trosse in kaart te bring. Allen (1998 MNRAS 296, 392) het ASCA- en ROSAT-data op 'n steekproef van 13 trosse gebruik om massametings van X-straal- en gravitasie-lense te vergelyk. Hy het uitstekende ooreenstemming gevind in vloei-trosse met afkoeling (wat sterk sentrale X-straal-helderheidspieke het), maar in vloei-trosse wat nie afkoel nie, is die sentrale massas wat uit die X-straaldata bepaal word, 2-4 keer kleiner as dié van sterk gravitasie-lens . In laasgenoemde gevalle is daar bewyse dat die X-straal-emitterende gas in 'n komplekse dinamiese toestand is, sodat die aannames wat gebruik word om die swaartekragpotensiaal uit die X-straaldata te bereken, nie geldig sal wees nie (sien ook Ota et al. 1998 ApJ 495, 170 Boehringer et al. 1998 A&A 334, 789). ASCA-data is ook gebruik om die teenwoordigheid van 'n heirargiese rangskikking van donker materie met 'n sentrale punt aan te dui (Ikebe et al. 1995 Nature 329, 427 Xu et al. 1998 ApJ 500, 738 Ikebe et al. 1998 ApJ, ingedien).

    Elementêre oorvloed

    Allen & Fabian (1998 MNRAS, in pers) het ASCA- en ROSAT-data gebruik om aan te toon dat koelvloei-trosse hoër emissie-geweegde metale het as stelsels met nie-koelvloei. Dit is waarskynlik te wyte aan die verkoeling van die koelstrome deur die toename in metaalvlakke in hul kern, waar die helderheid van die oppervlak skerp bereik word. In die AWM7 (Ezawa et al. 1997 ApJ 490, L33) en Perseus-trosse (Ezawa 1998 PhD-proefskrif), is daar ook 'n groter skaal met 'n groot hoogtepunt in verkoelingsstroomgroepe.

    Mushotzky & Loewenstein (1997 ApJ 481, L63) het die yster-oorvloed vir 'n groot aantal trosse gemeet en geen bewyse vir evolusie gevind nie, wat daarop dui dat die meeste verryking van die intra-clustermedium by rooiverskuiwings moes plaasvind> 1. Inderdaad 'n z

    1 X-straalgroep wat waargeneem is deur Hattori et al. (1997 Nature 388, 146) het 'n ystervloed in ooreenstemming met plaaslike voorwerpe. Hierdie groep is buitengewoon omdat dit 'n sterk X-straal-emitter is met gravitasie-lens sonder die verwagte populasie opties sigbare sterrestelsels.

    Swak groepe

    Vroeë tipe sterrestelsels

    300 kpc). Die M / L-verhouding is 22 binne 20 kpc en neem toe tot 300 in die waargenome mate van die sterrestelsel. Die uitgebreide aard van die emissie en die groot M / L maak die sterrestelsel 'n "donker groep".


    Watter breuk materie is nie gebind aan die sterrestelsels, groepe en trosse wat ons sien nie? - Sterrekunde

    Lesing 30: Groepe en trosse sterrestelsels

    Sterrestelsels vergader dikwels in Groepe & amp-trosse

    Die Melkweg is deel van die Plaaslike groep

    Groepe: 3 tot 30 helder sterrestelsels

    Trosse: & gt 30 (tot 1000 s) helder sterrestelsels

    Superclusters: Clusters of Clusters

    X-straalgas in trosse en groepe

    Groepe en sterrestelsels

    Die meeste sterrestelsels word in groepe en groepe gevind

    o Groepe: 3 tot 30 helder sterrestelsels

    o Trosse: 30 tot 300+ helder sterrestelsels

    o Groottes: 1-10 Mpc breed (ons Galaxy is

    o Bevat dikwels baie meer dwergstelsels

    3000 trosse is tot op hede gekatalogiseer.

    Net omdat daar enkele sterrestelsels naby mekaar in die lug is, beteken dit nie dat daar 'n groep moet wees nie. Dit kan 'n toevallige superposisie wees. Hulle moet op dieselfde afstand en gravitasiegebonde wees.

    Groep van & GT 45 sterrestelsels, insluitend die Melkweg en Andromeda

    o 5 helder sterrestelsels (M31, MW, M33, LMC, IC10)

    o & gt23 elliptiese (4 dE's & amp & gt19 dSph)

    o 14 onreëlmatighede van verskillende groottes

    Plaaslike groepdiagram (sien Figuur 26-17). Let op dat baie van die dE's en dSphs naby M31 (= Andromeda) en die Melkweg is.

    Naaste groot groep aan die plaaslike groep

    Relatief los groepering, gesentreer op twee helder elliptiese vorms: M87 en amp M84

    o 2500 sterrestelsels (meestal dwerge)

    Sien Figuur 26-16 vir 'n voorbeeld

    Bevat 1000 sterre sterrestelsels:

    o Massas tot 10 15 MSon

    o Een of meer reuse Elliptiese sterrestelsels in die middel

    o Elliptiese middels naby die sentrum gevind

    o Spirale aan die buitewyke gevind

    10-20% van hul massa is in die vorm van 'n baie warm (10 7 -10 8 K) intrakluster gas wat slegs teen X-straal golflengtes gesien word.

    Helderste sterrestelsels

    Die sentrums van trosse word gewoonlik deur een of twee oorheers reuse elliptiese middels.

    Hierdie elliptiese middels het meer as tien keer die massa van die melkweg en is op sigself groter as die hele plaaslike groep.

    Swaartekrag trek sterrestelsels saam

    Kyk na die film van swaartekrag wat sterrestelsels in 'n groep van Tom Quinn aan die Universiteit van Washington intrek op hpcc.astro.washington.edu/faculty/trq/toden.mpeg

    Let op dat die sterrestelsels gevorm het lank voordat dit in die groep getrek word. Hierdie film wys wat met die donker materie en sterre gebeur, nie met die gas nie.

    Verhitting deur fotone (lig). Die warmste sterre kan gas tot 10 000 K verhit.

    Sigbare lig geproduseer! Maak geïoniseerde waterstof.

    In trosse is daar verhitting deur botsings en skokke

    Skokke kan gas tot miljoene grade verhit. X-strale!

    Opmerking: X-straalspektrum is nie 'n swartliggaam nie. Die gas is nie dig genoeg nie.

    Gasbotsing as tros vorm

    Kyk na die film van swaartekrag wat gas saamtrek, en gas wat bots

    Aangesien swaartekrag die sterrestelsels saamtrek om 'n groep te vorm, breek die gas in daardie sterrestelsels in ander gas in. Skokke verhit die gas.

    Ryk trosse kan baie materie in die warm röntgengas bevat.

    X-straalgas kan gebruik word om trosse te vind en kanslynings te vermy. As swaartekrag nie sterrestelsels saamgetrek het nie, geen botsings van gas en geen röntgenstrale nie.

    Die röntgengas is nie baie dig nie. Dit het 'n emissielynspektrum wat gebruik kan word om die samestelling daarvan te bestudeer.

    Groepe kan ook warm X-straalgas hê.

    Gewoonlik is dit 'n baie kleiner fraksie van die groepmassa en nie al die sterrestelsels in die groep nie.

    Neutrale waterstof in groepe

    Groepe sterrestelsels kan baie neutrale waterstofgas bevat.

    As ons die emissie op 21 cm waarneem, kan ons kaarte maak wat die verspreiding van gas in groepe toon.

    Hierdie sterrestelsels is beslis verbind!

    Die Melkweg en sy satelliete, die LMC en SMC, is ook verbind deur neutrale waterstofgas.

    Elliptiese middels kom baie meer voor in trosse as in die veld. Hoe ryker die groep, hoe meer elliptiese en S0's.

    Helder sterrestelsels in ryk trosse

    Byna seker as gevolg van die omgewing van trosse. In trosse is sterrestelsels in wisselwerking, versmelt en teister. Spirale vind dit moeilik om te oorleef. (Volgende klas bespreek meer besonderhede oor die prosesse).

    Motions of Galaxies in Clusters

    Net soos binêre sterre wentel om hul massamiddelpunt, of sterre wentel om 'n sterrestelsel, sal sterrestelsels in 'n groep om hul trossentrum wentel.

    Ons kan hierdie bewegings (ten minste die radiale!) Meet deur die Doppler-verskuiwing in die geïntegreerde lig.

    Snelhede van meer as 1000 km / s relatief tot die cluster sentrum.

    Bewyse vir donker materie in clusters of galaxies

    Baie bewyse toon die teenwoordigheid van donker materie in trosse. Dit is nie verbasend nie, aangesien die individuele sterrestelsels donker materie het.

    Snelhede van sterrestelsels (snelheidsverspreiding)

    Sterrestelsels beweeg baie vinnig. Donker materie is nodig om hulle aan die groep te hou.

    Gasatome baie warm (= beweeg baie vinnig). Donker materiaal is nodig om die gas aan die groep vas te hou.

    Swaartekraglens (sien Algemene Relatiwiteit)

    o Massas van 10 15 tot 10 16 MSon

    o Dikwels lang en gloeiend van vorm

    Grootste samehangende (maar nog nie gravitasiegebonde) strukture in die heelal

    Grofweg gesentreer op die Virgo Cluster

    5% van die volume word deur sterrestelsels beset

    Die Local Group is aan die buitewyke van die Local Supercluster geleë en val in die Virgo Cluster

    Die heelal lyk skuim op die grootste skaal

    Groot kettings van superklusters

    5x minder sterrestelsels as in superklusters

    Een van die grootste strukture wat in die heelal bekend is

    Die bestaan ​​van 'Large Scale Structure' vertel ons iets oor hoe sterrestelsels gevorm word.


    Inhoud

    Stephans Quitet, 'n klassieke voorbeeld van 'n kompakte groep. (Geneem deur HST)

    Kompakte groepe [wysig | wysig bron]

    A & # 160kompakte groep& # 160 bestaan ​​uit 'n klein aantal sterrestelsels, gewoonlik ongeveer vyf, naby en relatief geïsoleerd van ander sterrestelsels en formasies. Die eerste kompakte groep wat ontdek is, was & # 160Stephan's Quintet, wat in 1877 gevind is. & # 160Stephan's Quintet is vernoem na 'n kompakte groep van vier sterrestelsels plus 'n nie-verbonde voorgrondstelsel. Sterrekundige Paul Hickson het in 1982 'n katalogus van sulke groepe, die & # 160Hickson Compact Groups, opgestel.

    Kompakte groepe sterrestelsels toon maklik die effek van donker materie, aangesien die sigbare massa baie minder is as wat nodig is om die sterrestelsels in 'n gebonde groep bymekaar te hou. Kompakte sterrestelsegroepe is ook nie dinamies stabiel oor & # 160Hubble-tyd nie, en dit wys dus dat sterrestelsels deur samesmelting ontwikkel oor die tydskaal van die ouderdom van die heelal.

    Fossielgroepe [wysig | wysig bron]

    Fossiele groepe is geneig om te bestaan ​​uit 'n groot, geïsoleerde & # 160elliptiese sterrestelsel & # 160; ingebed in 'n uitgebreide stralekrans van röntgenfoto's wat die grootte van 'n sterrestelselgroep uitstraal. Hulle is vermoedelik die gevolg van die uitgebreide samesmelting van al die & # 160galaxies & # 160 wat in 'n klein groepie voorkom, met die uitgebreide X-straalstralekrans wat sterk bewys lewer vir die oorsprong van die groep.

    Die sentrale elliptiese sterrestelsel in 'n fossielgroep is net so helder soos 'n helderste sterrestelsel, maar beskik nie oor die uitgebreide & # 160stellêre stralekrans & # 160 wat dikwels met sulke sterrestelsels geassosieer word nie.

    Die groot elliptiese sterrestelsel NGC 4555 is 'n goeie voorbeeld, want in X-straal vertoon lig 'n groot stralekrans wat die konsep van fossiele groepe sterk ondersteun.

    Voorgroepe [wysig | wysig bron]

    Voorgroepe is groepe sterrestelsels wat besig is om te vorm. Dit is 'n kleiner vorm van protoklusters.


    Kyk deur die lens

    Sterrestelsels is massief, maar ook relatief kompak. Alhoewel hulle geen skerp gedefinieerde rande het nie, strek dit oor die algemeen 'n paar tien miljoene ligjare. OK, goed, dit is vir ons mense groot, maar dit is redelik klein in vergelyking met die kosmos.

    Hierdie kompaktheid maak trosse uitstekend swaartekraglense. Deur Albert Einstein se algemene relatiwiteitsteorie weet ons dat massiewe voorwerpe soos lense optree en die pad van enige weidende ligstrale buig. Hoeveel die lig gebuig word, hang af van hoe massief die indringende voorwerp is, en deur die pad van agtergrondlig te bestudeer, kan ons uitvind hoe die saak versprei word, of u dit sien skyn of nie.

    En as ons na 'n tipiese sterrestelselgroep kyk, sien, dan sien ons allerlei lensstelsels. Die lig van agtergrondstelsels word skeefgetrek en verdraai op sy reis deur die groep, en vorm alles van elegante boë tot minder as elegante kronkels. Deur die verwronge vorms te vergelyk met dié wat sterrestelsels normaalweg het, kan ons rekonstrueer waaruit die groep bestaan ​​en waar al die ingewande is.

    Die resultaat, van tros tot tros oor die kosmos? Daar is baie meer as wat die oog sien. Die sterrestelsels en gas binne in 'n groep is nie naastenby genoeg om die uiterste kronkelende lig vanuit die agtergrond te verreken nie. Iets anders moet die trosse vul, sonder om enige eie lig uit te straal (anders sou ons dit gesien het). Dit moet saak maak, en dit moet donker wees.


    Die Groot Muur (van sterrestelsels, in Sloan)

    Titel: Sloan Great Wall as 'n kompleks van superklusters met ineenstortende kerne
    Skrywers: M. Einasto, H. Lietzen, M. Gramann, E. Tempel, E. Saar, L. J. Liivamägi, P. Heinämäki, P. Nurmi, J. Einasto
    Eerste outeur en instelling: Tartu-sterrewag, Tõravere, Estland
    Status: Aanvaar vir publikasie in Sterrekunde en Astrofisika

    The sheer scale of the universe is overwhelming. Much of the universe is filled with a complex web of matter—what cosmologists like to call the “structure” of the universe. Most everything we know and love—the wispy cloud in the sky, the bright nebulas that pierce the natal darkness of giant molecular clouds, the faint and distant galaxies—are gravitationally bound to something. One can continually zoom out to larger and larger scales, and you’ll see that objects that looked lonely on one scale are often surrounded with similar objects: our Sun is but one of the 200 billion stars the Milky Way Galaxy, which in turn is but one of about 50 galaxies in the Local Group, which in turn is one of 300-500 galaxy groups and clusters in the Laniakea Supercluster. But this is where the cosmic, fractal structure of hierarchically gravitationally bound objects ends. The largest structures we see in the universe—superclusters—enter into territory where gravity no longer reins, and all collections of matter at larger scales are subject to the expansion of the universe.

    These vast and massive superclusters are the objects of study of the authors of today’s paper. Clues to uncover the universe’s remaining secrets—such as the cosmological model and the processes that formed the present-day web—are encoded in the structures of superclusters. Superclusters are also the birthplaces of clusters, and the resultant structures therein. Thus the authors seek to study in detail such properties of superclusters. They turn to the closest collection of superclusters bursting with galaxies discovered in the Sloan Digital Sky Survey (SDSS), the eponym for the Sloan Great Wall (SGW) of galaxies, which contain galaxies spanning a redshift Z of 0.04 to 0.12.

    Figure 1. Galaxy groups (circles) in the Sloan Great Wall. The groups have been color coded by the supercluster they were identified to be in. The size of the circles denotes the spatial extent of the group as we would see them in the sky. Note the elongated morphologies of the superclusters. Figure taken from today’s paper.

    The authors uncovered a rich hierarchy of structure in the Great Wall. They find five superclusters with a luminosity density cutoff, all massive—accounting for invisible gas and galaxies too faint to detect, they estimate that these superclusters range in mass from about 10 15 M to a few 10 16 M—one to ten thousand times the mass of the Milky Way. Two of the superclusters are visibly “rich” and contain 2000-3000 galaxies each (superclusters 1 and 2 in Figure 1), while three are “poor,” containing just a few hundred visible galaxies.

    Using a novel method to identify how the galaxies cluster, they find that each supercluster in turn contains highly dense “cores” of galaxies. The rich superclusters contain several cores with tens to hundreds of galaxy groups and range from 10 14 M to a few 10 15 M. These cores in turn contain galaxy clusters, comprising a single galaxy cluster or containing multiple clusters. Within these cores are what astronomers would consider the first “true” structures—extremely dense regions which no longer grow with the expansion of the universe but instead collapse into bound objects. The authors derive density profiles for the cores in the rich superclusters and find that the inner 8 h -1 Mpc (about 2000 times larger than the Milky Way h -1 denotes the normalized Hubble constant) of each core is or will soon be collapsing.

    The superclusters are lush with mysterious order beyond their spatial hierarchy. One of the rich superclusters (#1 in Figure 1) appears to have a filamentary shape and which contains many red, old galaxies. The other rich supercluster (#2) is more spidery, a conglomeration of chains and clusters of galaxies, all connected, and contains more blue, young galaxies. These differences in shape and color could indicate that the superclusters have different dynamical histories. The largest objects of our universe remain to be further explored!


    Our Home Supercluster, Laniakea, Is Dissolving Before Our Eyes

    On the largest cosmic scales of all, planet Earth appears to be anything but special. Like hundreds of billions of other planets in our galaxy, we orbit our parent star like hundreds of billions of solar systems, we revolve around the galaxy like the majority of galaxies in the Universe, we’re bound together in either a group or cluster of galaxies. And, like most galactic groups and clusters, we’re a small part of a larger structure containing over 100,000 galaxies: a supercluster. Ours is named Laniakea: the Hawaiian word for “immense heaven.”

    Superclusters have been found and charted throughout our observable Universe, where they’re more than ten times as rich as the largest known clusters of galaxies. Unfortunately, owing to the presence of dark energy in the Universe, these superclusters ⁠ — including our own ⁠ — are only apparent structures. In reality, they’re mere phantasms, in the process of dissolving before our very eyes.

    The Universe as we know it began some 13.8 billion years ago with the Big Bang. It was filled with matter, antimatter, radiation, etc. all the particles and fields that we know of today, and possibly even more. From the earliest instants of the hot Big Bang, however, it wasn’t simply a uniform sea of these energetic quanta. Instead, there were tiny imperfections ⁠ — at about the 0.003% level ⁠ — on all scales, where some regions had slightly more or slightly less matter-and-energy than average.

    In each one of these regions, a great cosmic race ensued. The race was between two competing phenomena:

    1. the expanding Universe, on one hand, which works to drive all the matter and energy apart,
    2. and gravitation, which works to pull all forms of energy together, causing massive material to clump and cluster together.

    With both normal matter and dark matter populating our Universe ⁠ — but not in sufficient quantities to cause the entire Universe to recollapse ⁠ — our Universe first forms stars and star clusters, with the first ones appearing when less than 200 million years have passed since the Big Bang. Over the next few hundred million years, structure begins to appear on larger scales, with the first galaxies forming, star clusters merging together, and even galaxies growing to attract matter from the lower-density regions nearby.

    As time continues to pass, and we cross from hundreds of millions of years to billions of years in our measurement of time since the Big Bang, galaxies gravitate together to form the Universe’s first galaxy clusters. With up to thousands of Milky Way-sized galaxies in them, massive mergers form giant elliptical behemoths at the cores of these clusters. At the modern extremes, galaxies like IC 1101 can grow to quadrillions of solar masses.

    On even larger spatial scales and even longer timescales, the cosmic web begins to take shape, with filaments of dark matter tracing out a series of interconnecting lines. The dark matter drives the gravitational growth of the Universe, while the normal matter interacts through forces other than gravity as well, leading to the formation of gas clumps, new stars, and even new galaxies on long enough timescales.

    Meanwhile, the space between the filaments ⁠ — the underdense regions of the Universe ⁠ — give up their matter to the surrounding structures, becoming great cosmic voids. Galaxies dot the filaments, and fall into the larger cosmic structures where multiple filaments intersect. On long enough timescales, the most spectacular nexuses of matter even begin attracting one another, causing galaxy groups and clusters to begin forming even larger structures: galactic superclusters.

    Superclusters are collections of:

    all connected by great cosmic filaments that trace out the cosmic web. Their gravitation mutually attract these components towards a common center-of-mass, where these large structures span hundreds of millions of light-years and contain upwards of 100,000 galaxies apiece.

    If all that we had in the Universe were dark matter, normal matter, black holes, neutrinos and radiation ⁠ — where the combined gravitational effects of these components fought against the Universe’s expansion ⁠ — superclusters would eventually reign supreme. Given enough time, these enormous structures would mutually attract to the point where they all merged together, creating one enormous, bound cosmic structure of unparalleled proportions.

    In our own local corner of the Universe, the Milky Way can be found in a small neighborhood we call our local group. Andromeda is our local group’s largest galaxy, followed by the Milky Way at #2, the Triangulum galaxy at #3, and perhaps 60 significantly smaller dwarf galaxies strewn out over a volume spanning a few million light-years in three dimensions. Our local group is one of many small-ish groups in our vicinity, along with the M81 group, the Sculptor group, and the Maffei group.

    Larger groups ⁠ — like the Leo I group or the Canes II group ⁠ — are also abundant in our nearby surroundings, containing around a dozen large galaxies apiece. But the most dominant nearby structure is the Virgo Cluster of galaxies, containing more than a thousand galaxies comparable in size/mass to the Milky Way, and located just 50–60 million light-years away. The Virgo cluster is the main source of mass in our nearby Universe.

    But the Virgo cluster itself is just one of a large number of galaxy clusters, themselves collections of hundreds to thousands of large galaxies, that have been mapped out in the nearby Universe. The Centaurus cluster, the Perseus-Pisces cluster, the Norma cluster and the Antlia cluster represent some of the densest and largest concentrations of mass close to the Milky Way.

    They conform very well to this idea of the cosmic web, where “strings” of galaxies and groups exist along the filaments connecting these large clusters, and with giant voids in space separating these mass-containing regions from one another. These voids are tremendously underdense, while the nexuses of these filaments are excessively overdense it’s very clear that on cosmic timescales, the underdense regions have given up the majority of their matter to the denser, galaxy-rich clusters.

    In our larger galactic neighborhood, going out for around one or two hundred million light-years, all of these clusters (excepting Perseus-Pisces, which lies on the other side of a nearby void) appear to have filaments with galaxies and galactic groups between them. It appears to make up a much larger structure, and if you sum up every galaxy in it ⁠ — large and small ones alike ⁠ — we fully anticipate that the total number should exceed 100,000.

    This is the collection of matter that we refer to as Laniakea: our local supercluster. It links up our own massive cluster, the Virgo cluster, with the Centaurus cluster, the Great Attractor, the Norma Cluster and many others. It’s a beautiful idea that represents structures on scales larger than a visual inspection would reveal. But there’s a problem with the idea of Laniakea in particular and with superclusters in general: these are not real, bound structures, but only apparent structures that are currently in the process of dissolving away entirely.

    Our Universe isn’t just a race between an initial expansion and the counteracting gravitational force caused by matter and radiation. In addition, there’s also a positive form of energy that’s inherent to space itself: dark energy. It causes the recession of distant galaxies to speed up as time goes on. And ⁠ — perhaps most importantly ⁠ — it gets more important on larger scales and at later times, which is particularly relevant for the existence of superclusters.

    If there were no dark energy, Laniakea would most certainly be real. Over time, its galaxies and clusters would all mutually mutually attract, leading to an enormous grouping of 100,000+ galaxies, the likes of which our Universe has never seen. Unfortunately, dark energy became the dominant factor in our Universe’s evolution approximately 6 billion years ago, and the various components of the Laniakea supercluster are already accelerating away from one another. Every component of Laniakea, including every independent group and cluster mentioned in this article, is not gravitationally bound to any other.

    Every supercluster that we’ve ever identified are not only gravitationally unbound from one another, but they themselves are not gravitationally bound structures. The individual groups and clusters within a supercluster are unbound, meaning that as time goes on, each structure presently identified as a supercluster will eventually dissociate. For our own corner of the Universe, the Local Group will never merge with the Virgo cluster, the Leo I group, or any structure larger than our own.

    On the largest cosmic scales, enormous collections of galaxies spanning vast volumes of space appear to be real ⁠ — the Universe’s superclusters ⁠ — but these apparent structures are ephemeral and transient. They are not bound together, and they will never become so. In fact, if a structure had not already accumulated enough mass 6 billion years ago to become bound, when dark energy first dominated the Universe’s expansion, it never will. Billions of years from now, the individual supercluster components will be torn apart by the Universe’s expansion, forever adrift as lonesome islands in the great cosmic ocean.


    Categories

    Statistics

    Active galaxies pour out lots of energy, due to their central supermassive black holes gobbling down matter. Galaxies tend not to be loners, but instead exist in smaller groups and larger clusters. Our Milky Way is part of the Local Group, and will one day collide with the Andromeda galaxy. Clusters of galaxies also clump together to form superclusters, the largest structures in the Universe. In total, there are hundreds of billions of galaxies in the Universe.

    Table of Contents
    Black Holes at the Center of Galaxies 2:26
    Galaxies Are a Part of Small/Large Clusters 9:47
    The Milky Way is Part of the Local Group 6:45
    Galaxy Clusters Clump Together to Create Superclusters 11:03
    Hundreds of Billions of Galaxies 12:39

    PHOTOS/VIDEOS
    Galactic Wreckage in Stephan's Quintet http://hubblesite.org/newscenter/archive/releases/2009/25/image/x/ [credit: NASA, ESA, and the Hubble SM4 ERO Team]
    Best image of bright quasar 3C 273 http://www.spacetelescope.org/images/potw1346a/ [credit: ESA/Hubble & NASA]
    Nearby Quasar 3C 273 http://hubblesite.org/newscenter/archive/releases/2003/03/image/a/ [credit: NASA, M. Clampin (STScI), H. Ford (JHU), G. Illingworth (UCO/Lick Observatory), J. Krist (STScI), D. Ardila (JHU), D. Golimowski (JHU), the ACS Science Team, J. Bahcall (IAS) and ESA]
    Gamma Rays http://chandra.harvard.edu/photo/2014/archives/archives_herca.jpg [credit: X-ray: NASA/CXC/SAO, Optical: NASA/STScI, Radio: NSF/NRAO/VLA]
    Black hole (artist's impression) http://www.spacetelescope.org/videos/hst15_black_hole2/ [credit: ESA/Hubble (M. Kornmesser & L. L. Christensen)]
    Matter accreting around a supermassive black hole (artist's impression) http://www.spacetelescope.org/videos/hubblecast43c/ [credit: ESA/Hubble (M. Kornmesser)]
    Artist’s animation of galaxy with jets from a supermassive black hole http://www.spacetelescope.org/videos/heic1511a/ [credit: ESA/Hubble, L. Calçada (ESO)]
    NASA's Swift Finds 'Missing' Active Galaxies https://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=10698 [credit: NASA/Goddard Space Flight Center]
    Sagittarius A*: NASA's Chandra Detects Record-Breaking Outburst from Milky Way's Black Hole http://chandra.harvard.edu/photo/2015/sgra/ [credit: NASA/CXC/Amherst College/D.Haggard et al]
    NASA Hubble Sees Sparring Antennae Galaxies https://www.nasa.gov/content/goddard/nasa-hubble-sees-sparring-antennae-galaxies [credit: Hubble/European Space Agency]
    A New Dawn http://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=11011 [credit: NASA, ESA, G. Besla (Columbia University) and R. van der Marel (STScI)]
    Galaxy Sky http://svs.gsfc.nasa.gov/vis/a010000/a011000/a011011/hs-2012-20-h-full_1920x1080.jpg [credit: NASA, ESA, Z. Levay and R. van der Marel (STScI) T. Hallas, and A. Mellinger]
    Virgo Cluster http://deepskycolors.com/astro/2015/06/RBA_VirgoCluster3p_2048.jpg [credit: Rogelio Bernal Andreo]
    Cosmic Clumps http://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=11445 [credit: NASA's Scientific Visualization Studio]
    Laniakea: Our Home Supercluster of Galaxies http://apod.nasa.gov/apod/ap140910.html [credit: R. Brent Tully (U. Hawaii) et al., SDvision, DP, CEA/Saclay]
    Webb Science Simulations http://svs.gsfc.nasa.gov/vis/a010000/a010600/a010663/index.html [credit: NASA/Goddard Space Flight Center and the Advanced Visualization Laboratoy at the National Center for Supercomputing Applications]
    Hubble Deep Field https://upload.wikimedia.org/wikipedia/commons/5/5f/HubbleDeepField.800px.jpg [credit: R. Williams (STScI), the Hubble Deep Field Team and NASA]
    Hubble Ultra Deep Field 2014 http://hubblesite.org/newscenter/archive/releases/2014/27/image/a/ [credit: NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI)]

    Intro (0:00)

    Hey Astronomers! Phil Plait here.

    In our last episode I talked about galaxies - vast collections of gas, dust, and upwards of hundreds of billions of stars. We live in one, The Milky Way, a gigantic disk galaxy with sprawling spiral arms. Other galaxies are elliptical or irregular or peculiar, but those are classifications based on shape.

    We also classify galaxies on their behavior, and sometimes even on their location and mass. To understand why, we have to take a step back and look at the environments in which galaxies sometimes find themselves. And if you thought galaxies were big and powerful, well, I'm about to crush your brain again.

    Active Galaxies (0:52)

    In the 1960s, a peculiar object was found called 3C273. Through optical telescopes it looked like an unassuming blue star, but through a radio telescope it was seen to be ablaze with light - a luminous powerhouse. Stars didn't blast out that much radio radiation, so this was baffling. The mystery deepened when spectra of 3C273 were taken. It wasn't a star it was an entire galaxy, and not just any galaxy, but one very very far away - well over 2 billion light years.

    Far from being some dim thing, 3C273 revealed itself to be the most luminous object in the universe ever seen at that time. It blasts out over 4 trillion times the energy the Sun does. And yet it appears star-like, a mere dot in the sky. Because of this, it was dubbed a "quasi-stellar radio source," which is pretty underwhelming for the most powerful energy source in the entire cosmos.

    Happily, the name was shortened to "quasar," which you'll admit, is way cooler. Once 3C273 became known, lots more such objects were found. With the advent of x-ray observatories launched into space, even more energetic point sources were found, which is amazing. X-rays are a very high-energy flavor of light, and it takes a lot of power to make them.

    Eventually, galaxies like these were even found to be blasting out gamma rays, the very highest energy kind of light. Clearly, these were no regular galaxies. Astronomers gave them the generic name active galaxies and classified them into various sub-categories depending on how they emitted their light and what kind of spectra they had.

    But what could power these immensely energetic galaxies? It turns out, to create that kind of energy, you need to have an object with a lot of gravity. And what kind of object has a lot of gravity? (sinister laugh)

    In the 1980s, astronomers were getting suspicious that all large galaxies had very massive black holes in their cores. In fact, one of the reasons the Hubble space telescope was built and launched was to explore this idea and characterize (that is, find out as much as it could about) these black holes.

    Over time, we found this idea is absolutely correct. Every big galaxy we see appears to have a huge black hole in its heart. Even the smallest is a monster, with millions of times the Sun's mass, and some tip the cosmic scale at billions of solar masses.

    We now think that these supermassive black holes form at the same time galaxies do. As the material coalesces to create a galaxy, some falls to the center and feeds the black hole there. It grows as its host galaxy does.

    But I can hear you thinking, "Hey Phil, don't black holes suck down everything, even light itself? How could they power active galaxies, the brightest objects in the universe?" Ah, you can't escape from a black hole once you fall all the way in. Just outside the black hole's event horizon things can still get out.

    If a black hole is sitting all by its lonesome out in space it's, well, black. But if matter (like gas, dust, or even whole stars) falls into the black hole, it can be shredded by the fierce gravity. This material forms a flat disk called an accretion disk, the matter swirling madly at ferocious speeds before falling in, like water down a bathtub drain.

    Stuff closer to the black hole orbits faster than stuff farther out. This means material in the disk rubs together and heats up, just like rubbing your hands on a cold day warms them up via friction. But around a black hole, the orbital speeds are near the speed of light. Try rubbing your hands together at a couple of hundred thousand kilometers per second and see how much heat you make.

    So friction and other forces heat the material falling in to millions of degrees - so hot that it blasts out light across the electromagnetic spectrum, and that's what powers active galaxies. The black hole is the energy source, but the matter falling into it is the actual light bulb. Active galaxies are so bright, they can be seen clear across the universe.

    Not only that, but some active galaxies have jets. Magnetic fields coupled with the incredible rotation of the accretion disks can launch twin beams of matter and energy directly away from the black hole along the poles of the disk. These beams pack a huge wallop, traveling for hundreds of thousands of light-years. Eventually they slow down as they ram through the thin material between galaxies, but when they do they puff up. They look like huge cotton swabs, which glow in radio waves.

    Active galaxies can look pretty different from each other, and we now think that's due to our viewing angle on their accretion disk. When we see it edge on, the thick dust in the disk blocks the intense highest-energy light, but we do see lots of infrared as the radiation from the disk heats up clouds of dust around it. If the accretion disk is tipped a bit to our line of sight, we see more optical and high-energy light from it. And if the poles are aimed right at us, all that ridiculously energetic x- and gamma ray light can be seen.

    The Milky Way has a supermassive black hole in its heart too, with a mass of over 4 million times the Sun's. That might sound huge, but remember, the galaxy has hundreds of billions of stars in it. The black hole is only a teeny tiny fraction of the total mass of the Milky Way. Our black hole is quiescent (that is, not actively feeding) so we're not an active galaxy. Every now and again we'll see a flare from it as it swallows down a gas cloud or something like that, but nowhere near what's needed to switch it fully on. Happily, we appear to be safe from any tantrums it might throw. But that may not always be the case.

    One way to flip such a black hole from milquetoast to monster is through galactic collisions. When two galaxies collide, a lot of gas can be dumped into their centers where it can be gobbled down and heated up. We do see a lot of evidence that active galaxies are disturbed, as if they recently collided. So, could that happen to us?

    Yes, yes it can. In fact, it will, but not for a few billion more years. To understand that, we have to take a small step back. Well, actually a huge step back - a few million light years - and take a look at where galaxies live.

    Local Group (6:45)

    Our Milky Way isn't alone. It's part of a small knot of galaxies we call (in long, boring astronomical nomenclature tradition) the Local Group. It consists of a few dozen galaxies, most of which are small and dim, so faint that we're still discovering them. Two galaxies completely overpower the group: the Milky Way and the Andromeda Galaxy. The Local Group is elongated, almost dumbbell-shaped, with the Milky Way on one side and Andromeda on the other.

    In the past, the Local Group probably had lots more galaxies, but over the eons the two big galaxies ate them all, growing huge. Andromeda is bigger than we are and has more stars, but honestly we're both pretty big as galaxies go. And someday, we'll be bigger.

    The Andromeda Galaxy is about 2.5 million light years away, close enough that it can be seen by the naked eye on dark nights - the most distant object easily seen without aid. Spectra taken of Andromeda reveal an interesting fact. It's headed right for us!

    Its spectrum is blue-shifted, meaning it's approaching us, and it's doing so at quite a clip - about 100 km per second. That's fast, but 2.5 million light years is a long way. The collision is inevitable, but it won't happen for several billion years.

    When it does, both galaxies will stretch out due to galactic tides, forming long curving streamers of stars. They may pass by each other during the first pass, but over the next few hundred million years, they'll slow, fall back toward each other, and merge. They'll then form one much larger galaxy, probably an elliptical which astronomers have called "Milkomeda." I know that's awful, but if you can come up with a better name, let us know.

    Anyway, although this won't happen for billions of years, that's still long before the Sun dies. The Earth may still be around when the galaxies collide. It's not clear what will happen to us. The Sun may continue to lazily orbit the core of the new galaxy, or it may move farther in toward the center, or farther out in the galactic suburbs.

    And here's another fun fact: Andromeda has a gigantic black hole in its core too, which has 40 million solar masses - ten times the mass of ours. When the galaxies merge, the two monsters will probably go into orbit around one another. Not only that, but any gas and dust left over from star formation during the collision may fall toward the center of Milkomeda where the two black holes will gobble them down, and may turn the galaxy into an active one. Hopefully any death rays launched from that will miss Earth. But that won't happen for like 4 billion years anyway. I'm not too concerned over the fate of the Earth at that point.

    Galaxy Clusters and Superclusters (9:14)

    I feel that right now is a good time to give you a heads up. We're about to take a very VERY big step. Up to this point in the series, we've talked about some very big distances, millions or billions of kilometers to the planets, trillions of kilometers to the stars, and then jumping to thousands of light years (quadrillions or quintillions of kilometers) when talking about the galaxy itself.

    But those distances are as nothing when you start talking about intergalactic trips. We're about to venture out into the greater universe, and things are about to get very large.

    When we step outside our Milky Way, we find that a few galaxies have clumped together to form the Local Group. But as we look farther out into the universe, we see that galaxies tend to clump together on larger scales as well. Many are in small groups like ours, but sometimes they aggregate into much larger galaxy clusters. A typical galaxy cluster is a few tens of millions of light years across and can contain thousands of galaxies.

    The nearest one to us is the Virgo Cluster located about 50 million light years away in the direction of the constellation Virgo. It has well over a thousand galaxies in it, maybe twice that much. It may have as many as a quadrillion stars in it.

    Like star clusters, galaxies and galaxy clusters are bound to the cluster by their own mutual gravity, and move through the cluster on long orbits that can take billions of years to complete. Thousands of clusters are known, and they contain every kind of galaxy imaginable: spirals, ellipticals, irregulars, peculiars, active galaxies.

    In many clusters, a huge elliptical galaxy sits right at the very center. This is probably the result of collisions between smaller galaxies. When they smack into each other, their velocities through the cluster tend to cancel out, like two cars hitting head-on and stopping, so they fall to the center. As more mass falls to the center, the galaxy there grows huge. As mind-boggling as this all is, we're not done.

    Surveys of the sky have revealed that not only do galaxies clump together in clusters, but clusters themselves fall into even bigger groups called superclusters.

    A supercluster usually has several dozen clusters making it up and are hundreds of millions of light years across. Our Local Group is near the Virgo Cluster, and both are part of the Virgo Supercluster. Recent observations indicate the Virgo Supercluster is actually only an appendage of the even larger Laniakea Supercluster, which may have 100,000 galaxies in it, stretching across 500 million light years.

    This new result is a bit controversial. I mean, it's hard to know exactly how big such a structure is, especially when we're inside it. But it gives you an idea of the vast sizes and distances we're talking about here.

    Superclusters themselves aren't just randomly distributed through the universe either. They appear to fall along tremendously long, interconnected and intersecting filaments, making the universe appear almost foamy on the biggest scales, like a sponge. In between the filaments are vast regions relatively empty of galaxies called voids.

    This cosmic, large-scale structure - its size, shape, distribution of matter, and more - holds clues to some of the biggest questions we can ask: What is the universe made of? How did it start? What is its eventual fate? These are questions we'll get to in future episodes very soon, and I promise you they'll stretch your mind like nothing you've ever encountered before.

    Hubble Deep Space (12:28)

    But before we wrap up, there's one more thing I want you to see. When you look at all these pictures of galaxies, of clusters, of superclusters, a question pops up: How many galaxies are there? Can we count them all?

    To help answer that question, back in the 1990s, astronomers used the Hubble Space Telescope. They pointed it toward the emptiest part of the sky they could, a spot with little or no stars, nebulae or galaxies in it. They then let it stare, simply collecting light from whatever it could see, letting light accumulate until incredibly faint objects could be detected.

    And what did it find? Wonder. Pure simple wonder. Oh yeah, and THOUSANDS of galaxies.

    This is the Hubble Deep Field. Mind you, the area of sky you see here is roughly the same as the apparent size of a grain of sand held in your palm with your arm outstretched. And yet, in that tiny section of sky, there are thousands of galaxies. Essentially everything you see in that image is a galaxy - a huge collection of gas, dust, and billions of stars.

    The Deep Field was repeated in different parts of the sky, and the result was always the same - crowds of galaxies, jostling for position, crammed together even in a tiny slice of the heavens. You can count all the galaxies in these deep fields, and then use them to extrapolate to the entire sky, giving you the total number of galaxies in the universe. And what do you get? Well, give or take, 100,000,000,000 galaxies. A hundred billion. And each with billions of stars.

    The universe is mind-crushingly huge, and yet here we are a part of it, learning more about it all the time. It's easy to think the universe is too big to comprehend, and makes us seem tiny and insignificant in comparison. To me, the opposite is true it's our curiosity about this enormous cosmos that makes us significant. We yearn to learn more, to seek out knowledge. that doesn't make us small, it makes us vast.

    Recap (14:24)

    Today you learned that active galaxies pour out lots of energy due to their central supermassive black holes gobbling down matter. Galaxies tend not to loners, but instead exist in smaller groups and larger clusters. Our Milky Way is part of the Local Group and will one day collide with the Andromeda Galaxy. Clusters of galaxies also clump together to form superclusters - the largest structures in the universe. In total, there are hundreds of billions of galaxies in the universe.

    Credits (14:50)

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    Kyk die video: 182nd Knowledge Seekers Workshop, Thursday, July 27, 2017 (November 2022).