Planetarna maglina

Planetarna maglina je emisiona maglina koja se sastoji od svetlećeg jonizovanog gasa koji se širi.[1] Ime je dobila zbog sličnosti sa izgledom planeta kada se posmatra kroz manji teleskop, ali nema nikakve veze sa planetama Sunčevog sistema.[2][3] One su relativno kratkotrajan fenomen, samo nekoliko desetina hiljada godina, u odnosu na tipični stelarni životni vek od nekoliko milijardi godina.

Animacija nastanka planetarne magline i belog patuljka

Posmatranja

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Planetarna maglina NGC 2392 poznata i pod imenom Eskim.

Planetarne magline su relativno tamni objekti i prividno mali objekti. Ni jedna nije vidljiva golim okom. Prva otkrivena planetarna maglina je bila Mesje 27 koju je otkrio Šarl Mesje 1764. godine. Posmatrane tadašnjim slabim i nesavršenim teleskopima, planetarne magline donekle su ličile na gasovite planete, posebin Uran i Neptun. Vilhelm Heršel, otkrivač Urana, uveo je naziv planetarna maglina u upotrebu. Naziv se zadržao do danas uprkos tome što se zna da su planetarne magline veoma različite od planeta.

Upotrebom spektroskopskih metoda u 19. veku počela se otkrivati narav planetarnih maglina. Pionir spektroskopije Vilijam Hagins prvi je počeo sa sistematskim posmatranjem različitih objekata. Njegova proučavanja zvezda otkrila su da one imaju kontinuirani spektar ispresecan mnogim tamnim linijama. Kasnije je otkrio da mnoge magline poput galaksije Andromede imaju spektar sličan zvezdama.

Kada je Hagins usmerio teleskop prema NGC 6543 (poznatoj i pod imenom maglina Mačje oko), uočio je znatno drugačiji spektar. Umesto kontinuiranog spektra otkrio je spektar sa malim brojem emisionih linija. Najsjajnija od tih linija bila je ona s talasnom dužinom od 500,7 nm koja nije odgovarala niti jednom tada poznatom elementu. Astronomi su te linije pripisali nepoznatom elementu kojeg su nazvali nebulijum. Na sličan je način otkriven i helijum prilikom spektroskopskih posmatranja Sunca.

Naučnici su uskoro uspeli da izoluju helijum na Zemlji ali ne i nebulijum. Uskoro su neki naučnici na početku 20. veka pretpostavili da emisiona linija od 500,7 nm odgovara poznatom elementu u nepoznatim uslovima.

Napredak fizike i izvršavanje određenih eksperimenata pokazalo je da linija od 500,7 nm odgovara dvostruko jonizovanom kiseoniku (O2+ ili OIII). Kako je takva jonizacija moguća samo u veoma retkom gasu to je bio direktan dokaz da se od takvog gasa sastoje planetarne magline. Spektroskopska posmatranja pokazala su i da se sve planetarne magline polagano šire.

Središte zvezda planetarnih maglina su veoma vruće ali i relativno tamno, što govori da su veoma male. Pokazalo da su te zvezde zapravo beli patuljci, užarena jezgra nekadašnjih zvezda.

Galerija

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Reference

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  1. ^ Frankowski & Soker 2009, str. 654–8
  2. ^ Kwok 2005, str. 271–8
  3. ^ Hubblesite.org 1997

Literatura

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Spoljašnje veze

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