Stilhed før stormen
Dette smukke billede viser galakserne NGC 799 (nederst) og NGC 800 (øverst), der ligger i stjernebilledet Cetus (Hvalfisken). Dette galaksepar blev først observeret af den amerikanske astronom Lewis Swift tilbage i 1885.
I en afstand på omkring 300 millioner lysår, ser vi disse galakser ovenfra så vi kan sætte ekstra meget pris på deres former. Ligesom vores galakse Mælkevejen er disse objekter begge spiralgalakser, der består af de karakteristiske lange spiralarme, der vikles ud fra en klar bule i midten. I de tydelige spiralarme ligger et stort antal varme, unge og blå stjerner, der dannes i stjernehobe (det er de små blå prikker der kan ses på dette billede), mens der findes en større og mere kompakt gruppe gamle, kolde og røde stjerner i den centrale bule, der næsten ligger i en kugle.
Ved første øjekast ser de to galakser næsten ens ud, men for at se forskellen bliver man nødt til at kigge på detaljerne. Udover den åbenlyse forskel i deres størrelse, er det kun NGC 799, der har en bjælkestruktur i den centrale bule, og spiralarme der udspringer fra bjælkens ender. Galaktiske bjælker menes at virke som en makanisme, der fører gas fra spiralarmene ind til midten, hvilket gør stjernedannelsen mere intens. En supernova blev også observeret i NGC 779 i 2004, og fik navnet SN2004dt.
En anden interessant forskellighed imellem de to galakser er antallet af spiralarme. Den lille NGC 800 har tre klare, knudrede spiralarme, mens NGC 799 kun har to relativt svage men samtidigt brede spiralarme. Spiralarmene begynder for enden af bjælken og fortsætter hele vejen rundt om midten, og danner en struktur der ligner en ring.
Mens spiralgalakserne på billedet ser ud til at ligge utroligt tæt på hinanden mens de lever idyllisk side om side, kunne dette dog ikke være længere fra sandheden. Vi kunne være vidne til stilheden før stormen. Vi ved ikke præcist hvad fremtiden vil bringe, men typisk vil to galakser, når de kommer tæt nok på hinanden, interagere over hundrede millioner af år, hvilket skyldes forstyrrelser fra tyngdekraften. I nogle tilfælde vil der kun ske små interaktioner, der vil forvrænge galakserne, mens kolliderende galakser andre gange vil samle sig til en enkelt ny galakse.
Dette billede er taget af FORS 1 instrumentet på 8,2-meter teleskopet Very Large Telescope (VLT) på toppen af Cerro Paranal i Chile. Instrumentet kombinerer billeder der er taget igennem tre filtre (B,V og R).
Kilde:ESO
Om billedet
| Id: | potw1332a |
| Sprog: | da |
| Type: | Observation |
| Udgivelsesdato: | 12. august 2013 10:00 |
| Størrelse: | 1980 x 1789 px |
Om objektet
| Navn: | NGC 799, NGC 800 |
| Type: | Local Universe : Galaxy : Type : Spiral |
| Afstand: | 300 million lysår |
| Constellation: | Cetus |
Baggrundsbilleder
Koordinater
| Position (RA): | 2 2 12.31 |
| Position (Dec): | 0° 6' 3.41" |
| Field of view: | 6.60 x 5.96 arcminutes |
| Orientering: | Nord er 180.0° droite fra lodret |
Farver & filtre
| Bånd | Teleskop |
|---|---|
| Optisk B | Very Large Telescope FORS1 |
| Optisk V | Very Large Telescope FORS1 |
| Optisk R | Very Large Telescope FORS1 |
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