Pressemeddelelse

De varme blå stjerner i Messier 47

17. december 2014

Her er en ung, åben stjernehob med både et drys klare blå stjerner og enkelte røde kæmpestjerner for kontrastens skyld. Det drejer sig om hoben Messier 47, og billedet er taget med Wide Field Imager-instrumentet på ESOs MPG/ESO 2,2m teleskop på La Silla Observatoriet i Chile.

Messier 47 befinder sig omkring 1600 lysår fra Jorden, i stjernebilledet Puppis (på dansk Agterstavnen til himmelmyternes skib Argo). Den første til at bemærke hoben var den italienske astronom Giovanni Battista Hodierna en gang før 1664, og den blev så uafhængigt af det opdaget af Charles Messier, som åbenbart ikke kendte til Hodiernas opdagelser.

M47 er en af de stjernefattigste åbne hobe, men den er klar og ret nem at få øje på. Der er kun omkring 50 stjerner synlige i et område, som er cirka 12 lysår i diameter. Andre hobe kan indeholde tusinder af stjerner indenfor et lignende område.

Det har ikke altid været let at finde Messier 47, og faktisk mente man i en årrække at den var "væk", fordi Messier havde angivet koordinaterne forkert. Senere blev hoben genopdaget, og den fik et andet navne; NGC 2422. Det var først i 1959 at canadieren T. F. Morris fastslog, at de to hobe M47 og NGC 2422 var de samme, og han fandt ud af, hvad det var, Messier havde angivet forkert.

Although it is bright and easy to see, Messier 47 is one of the least densely populated open clusters. Only around 50 stars are visible in a region about 12 light-years across, compared to other similar objects which can contain thousands of stars.

Stjernernes klare blåhvide farver er tegn på deres høje temperatur. Jo varmere des mere blå, og jo koldere des mere røde. Dette forhold imellem farve, lysstyrke og temperatur kan beskrives med den kendte Planckkurve. Men ved hjælp af den meget mere detaljerede metode for studie af stjernefarver, som kaldes spektroskopi, kan astronomerne lære meget mere - hvor hurtigt stjernerne drejer rundt, og deres grundstofsammensætning blandt andet. På billedet findes også nogle få røde stjerner. Det er røde kæmper, som er nået længere igennem deres livscyklus end de lettere og mere langlivede blå stjerner [1].
M47 ser ud til at befinde sig tæt ved en anden stjernehob; Messier 46, men den sidstnævnte er meget længere væk (omkring 5.500 lysår) og den indeholder mange flere stjerner - mindst 500. Selvom der er meget flere stjerner, ser hoben svagere ud, men det skyldes afstanden.

På sin vis kunne man kalde M46 for M47s ældre søster. Den første er 300 millioner år gammel, og den anden er kun 78 millioner år. Derfor er de tungeste og klareste af stjernerne i M46 allerede kommet så langt i deres korte liv, at de er blevet usynlige, og mange af de andre er rødere og koldere på overfladen.

Billedet af Messier 47 er optaget som en del af  ESO Cosmic Gems programmet [2].

Noter

[1] En stjernes levetid afhænger først og fremmest af, hvor meget den vejer. Tunge stjerner, med en masse flere gange Solens har korte liv, som kan måles i millioner af år. Modsat kan meget lettere stjerner skinne i mange milliarder år. I en stjernehob er alle stjerner dannet omtrent samtidigt, og de har samme grundstofsammensætning, så de klare tunge stjerner udvikler sig hurtigst til røde kæmper, og de slutter deres liv tidligere. Tilbage er så de lettere og koldere stjerner.

 [2]  ESO Cosmic Gems programmet er en formidlingsaktivitet, som ESO har iværksat for at skaffe interessante, spændende og flotte billeder ved hjælp af ESOs teleskoper, til glæde for uddannelsessektoren og offentligheden. I programmet bruges observationstid, som af en eller anden grund alligevel ikke kan bruges til videnskabelige målinger. Billederne kan dog bruges af forskere, og kan leveres via ESOs videnskabelige arkiv.

Mere information

ESO er den fremmeste fællesnationale astronomiorganisation i Europa, og verdens langt mest produktive jordbaserede astronomiske observatorium. 15 lande er med i ESO: Belgien, Brazilien, Danmark, Finland, Frankrig, Italien, Nederlandene, Portugal, Spanien, Sverige, Schweiz, Storbritannien, Tjekkiet, Tyskland og Østrig. ESO har et ambitiøst program, som gør det muligt for astronomer at gøre vigtige videnskabelige opdagelser. Programmet har focus på design, konstruktion og drift af stærke jordbaserede observatorier. Desuden har ESO en ledende rolle i formidling og organisering af samarbejde omkring astronomisk forskning. ESO driver tre enestående observatorier i verdensklasse i Chile: La Silla, Paranal og Chajnantor. På Paranal driver ESO VLT, Very Large Telescope, som er verdens mest avancerede observatorium for synligt lys, samt to oversigtsteleskoper. VISTA, som observerer i infrarødt, er verdens største oversigtsteleskop, og VLT Survey Teleskopet er det største teleskop bygget til at overvåge himlen i synligt lys. ESO er Europas partner i ALMA, som er det største eksisterende astronomiprojekt. For tiden planlægges E-ELT, et 39 m optisk og nærinfrarødt teleskop, som bliver "verdens største himmeløje".

 

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Kontakter

Richard Hook
ESO 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

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Dette er en oversættelse af ESO pressemeddelelse eso1441 lavet af ESON - et netværk af personer i ESOs medlemslande, der er kontaktpunkter for medierne i forbindelse med ESO nyheder, pressemeddelelser mm.

Om pressemeddelelsen

Pressemeddelelse nr.:eso1441da
Navn:M 47
Type:Milky Way : Star : Grouping : Cluster : Open
Facility:MPG/ESO 2.2-metre telescope
Instruments:WFI

Billeder

Stjernehoben Messier 47
Stjernehoben Messier 47
De klare stjernehobe Messier 47 og Messier 46 i stjernebilledet Puppis
De klare stjernehobe Messier 47 og Messier 46 i stjernebilledet Puppis
Vidvinkeloptagelse af de klare stjernehobe Messier 47 and Messier 46
Vidvinkeloptagelse af de klare stjernehobe Messier 47 and Messier 46

Videoer

Zoom-ind på stjernehoben Messier 47
Zoom-ind på stjernehoben Messier 47
Panorering i den klare stjernehob Messier 47
Panorering i den klare stjernehob Messier 47

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