Pressemeddelelse
NGC 247’s støvede skive
2. marts 2011
Dette billede af NGC 247 er taget med Wide Field Imager på MPG/ESO 2,2 meter teleskopet på ESO’s La Silla-observatorium. Billedet afslører de fine detaljer i denne spiralgalakse og dens flotte baggrund. Astronomer mener, at galaksens store hældning set fra Jorden kan forklare, hvorfor afstanden til denne markante galakse tidligere er blevet overvurderet.
Spiralgalaksen NGC 247 er en af de nærmeste spiralgalakser på den sydlige himmel. I dette nye billede fra Wide Field Imager (WFI) på MPG/ESO 2.2 meter teleskopet i Chile kan mange af galaksens stjerner tydeligt ses. Desuden ses mange brintskyer i de løse og forrevne spiralarme. Skyerne, der gløder i pink nuancer, markerer områder, hvor nye stjerner bliver dannet.
NGC 247 er en del af Sculptor-gruppen, der er en gruppe af galakser omkring Sculptor-galaksen (NGC 253, som kan ses i pressemeddelelserne ”Frantic activity revealed in dusty stellar factories” og ”VISTA ser på Sculptor-galaksen”). Sculptor-gruppen er den nærmeste galakse-gruppe i forhold til vores egen Lokale Gruppe, der blandt andet tæller Mælkevejen. Men selv i dette tilfælde er det vanskeligt at sætte et præcist tal på den kosmiske afstand.
For at måle afstanden fra Jorden til en nærtliggende galakse er astronomerne nødt til at sætte deres lid til, at en type af variable stjerner, der kaldes cepheider, kan fungere som afstandsmålere. Cepheider er meget lysstærke stjerner, hvis lysstyrke varierer i faste intervaller. Den tid, det tager for en stjerne at lyse op og falme igen, kan beskrives med en simpel matematisk ligning, der giver stjernens egentlige lysstyrke. Når dette resultat sammenholdes med den målte lysstyrke, kan afstanden til stjernen beregnes. Denne metode er dog ikke fejlfri, da astronomer mener, at sammenhængen mellem svingningsperiode og lysstyrke afhænger af cepheidens sammensætning.
Et andet problem bunder i, at noget af lyset fra en cepheide på dets vej til Jorden kan blive absorberet af støv. Det får stjernen til at fremstå svagere og dermed synes længere væk, end den reelt er. Det er et særligt problem for NGC 247 med dens store hældning, da synslinien til cepheiderne går gennem galaksens støvskive.
Netop nu er et hold af astronomer imidlertid i færd med at se nærmere på de faktorer, der påvirker disse kosmiske afstandsmålere i en undersøgelse, der kaldes Araucaria-projektet [1]. Holdet har allerede rapporteret, at NGC 247 er mere end en million lysår tættere på Mælkevejen end tidligere antaget. Det bringer afstanden ned på lige over 11 millioner lysår.
Ud over hovedgalaksen indeholder dette billede også talrige galakser, der ligger langt bagved NGC 247. I øverste højre hjørne af billedet danner tre markante spiralgalakser en linje, mens der endnu længere ude, langt bag spiralerne, kan ses mange flere galakser, hvoraf nogle ses gennem NGC 247’s skive.
Dette farvebillede er en kombination af et stort antal af enkeltoptagelser taget gennem et blåt, et gul-grønt og et rødt filter over en periode på mange år. Billederne er suppleret med optagelser gennem et filter, der isolerer lyset fra den glødende brintgas, og her gengivet med røde farver. Den totale eksponeringstid pr. filter var henholdsvis 20 timer, 19 timer, 25 minutter og 35 minutter.
Noter
[1] Araucaria-projektet er et samarbejde mellem astronomer fra institutioner i Chile, USA og Europa. ESO’s Very Large Telescope (VLT) har leveret data til projektet.
Mere information
ESO, det Europæiske Syd Observatorium, er den mest fremtrædende internationale astronomi-organisation i Europa og verdens mest produktive astronomiske observatorium. ESO har i dag følgende 14 medlemslande: Belgien, Danmark, Finland, Frankrig, Holland, Italien, Portugal, Schweiz og Storbritannien, Spanien, Sverige, Tjekkiet, Tyskland og Østrig. Flere lande har udtrykt interesse i medlemskab. ESO’s aktiviteter er fokuseret på design, konstruktion og drift af jordbaserede observationsfaciliteter for astronomi for at muliggøre vigtige videnskabelige opdagelser. ESO spiller også en ledende rolle for at fremme og organisere samarbejdet inden for astronomisk forskning. I Chile driver ESO tre unikke observatorier i verdensklasse: La Silla, Paranal og Chajnantor. På Paranal driver ESO Very Large Telescope (VLT), der er verdens mest avancerede astronomiske observatorium til observationer i synligt lys. ESO er den europæiske partner i et revolutionerede astronomisk teleskop kaldet ALMA, det største igangværende astronomiske projekt. ESO planlægger i øjeblikket et 42 meter optisk/nær-infrarødt teleskop kaldet European Extremely Large Telescope (E-ELT), der vil blive ”verdens største øje mod himlen”.
Links
Kontakter
Richard Hook
ESO, La Silla, Paranal, E-ELT and Survey Telescopes Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
E-mail: rhook@eso.org
Ole J. Knudsen (Pressekontakt Danmark)
ESOs formidlingsnetværk
og Aarhus Space Centre, Aarhus Universitet
Aarhus, Danmark
Tel: +45 8715 5597
E-mail: eson-denmark@eso.org
Om pressemeddelelsen
| Pressemeddelelse nr.: | eso1107da |
| Navn: | NGC 247 |
| Type: | Local Universe : Galaxy : Type : Spiral |
| Facility: | MPG/ESO 2.2-metre telescope |
| Instruments: | WFI |
| Science data: | 2009ApJ...700.1141G |
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