Unge stjerner afsløret i tæt omfavnelse
For første gang har astronomerne observeret en skive af støv omkring det, som er ved at blive til et flerdobbelt stjernesystem. På billedet man ser hvordan! Billedet er baseret på nye observationer fra Atacama Large Millimeter/submillimeter Array (ALMA) i Chile.
Stjerner dannes i kosmiske skyer af gasarter og støv, når de spredte materiale i skyerne kollapser; trukket sammen af tyngdekræfterne. Områder med tættere stof har større tyngdekraft, og trækker dermed endnu mere stof til sig. Materialet danner en roterende skive omkring det, som bliver til en ung stjerne, og skivens stof bliver så langsomt omdannet til planeter eller falder ind i stjernen. I den sidste ende får den unge stjerne samlet nok stof til at temperaturen og trykket i det indre bliver store nok til at starte kernefusionen.
Singlestjerner - som Solen - er ikke så almindelige, som vi en gang troede. Faktisk har næsten halvdelen af stjernerne i vores Mælkevej mindst een ledsager, og nogen af dem er endnu mere selskabelige! Tidligere undersøgelser har vist, at stjernerne i flerstjernesystemer for det meste er enten relativt tæt på hinanden (i størrelsesordenen 500 gange afstanden imellem Jorden og Solen) eller betydeligt længere fra hinanden; mere end 1 000 AU (1 Astronomisk enhed eller AU er gennemsnitsafstanden imellem Jorden og Solen; 149,6 millioner kilometer).
At der er sådan to grupper af vidst forskellige afstande har fået forskerne til at konkludere, at der er to forskellige bestemmende fænomener, som danner flerstjernesystemerne. Enten har den oprindelige sky været ustabil og skæv under kollapset, og derfor er den splittet op, eller også er skiven omkring en oprindelig større protostjerne splittet op, også på grund af ustabiliteter. Den første proces vil give større stjerneafstande (som det også er antydet i nyere observationer), og den anden proces vil forårsage de meget tætte stjernefamilier (men det har vi hidtil ikke haft så mange indicier på).
De nye data fra ALMA har hjulpet på sagen, og har bekræftet antagelsen. Billedet viser den anden proces i funktion; her i det unge tredobbelte stjernesystem L1448 IRS3B. De tre stjerner ligger stadig dybt inde i den oprindelige støv- og gassky, i stjernebilledet Perseus, og omkring 750 lysår fra Jorden. Stjernerne guffer lystigt materiale i sig fra den omgivende skive. ALMA viser klart, at skiven har spiralstruktur, og det er tegn på at der er foråsaget af tyngdekræfterne.
Noter
ALMA, Atacama Large Millimeter/submillimeter Array, er et internationalt astronomisk observatorium, med ESO, US National Science Foundation (NSF) og National Institutes of Natural Sciences (NINS) i Japan i samarbejde med Chile. ALMAs finansieres af ESO (Det europæiske sydobservatorium), NSF i samarbejde med Canadas National Research Council og National Science Council i Taiwan, og af NINS i samarbejde med Academia Sinica i Taiwan og Korea Astronomy and Space Science Institute (KASI).
Opbygning og drift af ALMA styres af ESO på vegne af medlemstaterne, af National Radio Observatory ved Associated Universities, Inc. på vegne af Nordamerika og af National Astronomical Observatory i Japan på vegne af Østasien. Organisationen Joint ALMA Observatory, JAO står for den fælles ledelse og styring af konstruktion og drift af ALMA.
Links
- Artiklen, som fortæller mere: “A triple protostar system formed via fragmentation of a gravitationally unstable disk”, af J. Tobin et al., offentliggjort den 27. oktober 2016 i tidsskriftet Nature.
- NRAO pressemeddelelse
ALMA (ESO/NAOJ/NRAO)/J.J. Tobin (University of Oklahoma/Leiden University)
Om billedet
| Id: | potw1644a |
| Sprog: | da |
| Type: | Observation |
| Udgivelsesdato: | 31. oktober 2016 06:00 |
| Størrelse: | 1200 x 1204 px |
Om objektet
| Navn: | [BC86b] LDN 1448 IRS 3B, L1448 IRS3B |
| Type: | Milky Way : Star : Evolutionary Stage : Protostar Milky Way : Star : Grouping : Multiple |
| Afstand: | 750 lysår |
| Constellation: | Aries |
Baggrundsbilleder
Koordinater
| Position (RA): | 3 25 36.36 |
| Position (Dec): | 30° 45' 14.92" |
| Field of view: | 0.07 x 0.07 arcminutes |
| Orientering: | Nord er -0.0° venstre fra lodret |
Farver & filtre
| Bånd | Bølgelængde | Teleskop |
|---|---|---|
| Milimeter | 1.5 mm | Atacama Large Millimeter/submillimeter Array |
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