Pressemeddelelse

Et par meget kølige brune dværge

23. marts 2011

Observationer lavet med det Europæiske Syd Observatoriums Very Large Telescope sammen med to andre teleskoper har fundet en ny kandidat til titlen som den koldeste, kendte stjerne: En brun dværg i et dobbeltsystem, der har cirka samme temperatur som en frisklavet kop te – varm for et menneske, men ekstremt kold for en stjerneoverflade. Dette objekt er køligt nok til at krydse den diffuse linje, der adskiller kolde stjerner fra store, varme planeter.

Brune dværge er i bund og grund mislykkede stjerner: De er ikke tunge nok til, at deres tyngdekraft kan starte de kernereaktioner, der får stjerner til at lyse. Den nyligt opdagede brune dværg, der kaldes CFBDSIR 1458+10B, er det lyssvageste medlem af et dobbeltsystem af brune dværge, der befinder sig kun 75 lysår fra Jorden [1].

Den effektive X-shooter-spektograf på ESO’s Very Large Telescope (VLT) er brugt til at vise, at det sammensatte objekt er meget koldt set ud fra standarden for brune dværge. ”Vi var meget begejstrede for at se, at dette objekt har så lav en temperatur, men vi havde aldrig gættet, at det ville vise sig at være et dobbeltsystem med en endnu mere interessant og endnu koldere komponent,” siger Philippe Delorme fra Institut de planétologie et d’astrophysique de Grenoble (DNRS/Université Joseph Fourier), en af medforfatterne til den videnskabelige artikel, som beskriver disse nye målinger. CFBDSIR 1458+10 er den koldeste brune dværg, der endnu er opdaget.

Den lyssvageste af de to brune dværge har nu fået bestemt sin temperatur til omkring 100 grader Celsius, hvilket svarer til vands kogepunkt og er ikke meget anderledes end det indvendige af en sauna [2].”Ved sådanne temperaturer forventer vi, at den brune dværg har egenskaber, der adskiller sig fra tidligere kendte brune dværge og i stedet har egenskaber, der ligger tæt op af de store exoplaneters – den kan endda have vandskyer i sin atmosfære,” siger Michael Liu fra Institute for Astronomy på University of Hawaii, som er hovedforfatter på den videnskabelige artikel. ”Faktisk forventer jeg, at når vi i den nære fremtid begynder at tage billeder af gaskæmper omkring sollignende stjerner, vil mange af dem ligne CFBDSIR 1458+10B.”

At afdække hemmelighederne ved dette unikke objekt krævede den kombinerede styrke af tre forskellige teleskoper. CFBDSIR 1458+10 blev først opdaget som dobbeltsystem ved brug af det adaptive optiske system Laser Guide Star (LGS) på Keck II-teleskopet i Hawaii [3]. Liu og hans kolleger gjorde herefter brug af Canada-France-Hawaii-teleskopet, også i Hawaii, for at bestemme afstanden til den brune dværg-duo ved hjælp af et infrarødt kamera [4]. Endelig blev ESO’s VLT brugt til at studere objektets infrarøde spektrum og måle dets temperatur.

Jagten på kølige objekter er et meget varmt astronomisk forskningstema. Rumteleskopet Spitzer har for nylig identificeret to andre meget lyssvage objekter, som også er kandidater til titlen som den køligste kendte brune dværg, selv om deres temperaturer ikke er blevet målt så præcist. Fremtidige observationer vil give bedre mulighed for at bedømme, hvordan disse objekter kan sammenlignes med CFBDSIR 1458+10B. Liu og hans kolleger planlægger at undersøge CFBDSIR 1458+10B igen for bedre at kunne bedømme dens egenskaber og begynde at kortlægge dobbeltsystemets omløb, der efter 10 år med målinger skulle give astronomerne mulighed for at bestemme dobbeltsystemets masse.

Noter

[1] CFBDSIR 1458+10 er navnet på dobbeltsystemet. De to komponenter i systemet kaldes CFBDSIR 1458+10A og CFBDSIR 1458+10B, hvoraf sidstnævnte er den lyssvageste og køligste af de to. De lader til at kredse om hinanden i en afstand, som svarer til omtrent tre gange afstanden mellem Solen og Jorden med en periode på omkring 30 år.

[2] Til sammenligning er temperaturen på Solens overflade omkring 5500 grader Celsius.

[3] Adaptiv optik korrigerer for en stor del af de forstyrrelser, der skabes af Jordens atmosfære og forbedrer derved billedskarpheden med en faktor 10. Det gør det muligt at opløse af den meget lille afstand mellem dobbeltsystemets medlemmer.

[4] Astronomerne målte den tilsyneladende bevægelse af de brune dværge mod baggrunden af fjernere stjerner, der er et resultat af Jordens skiftende position i sit kredsløb rundt om Solen. Effekten, der kaldes parallakse, giver mulighed for at bedømme afstanden til de brune dværgstjerner.

Mere information

Denne undersøgelse er præsenteret i den videnskabelige artikel ”CFBDSIR J1458+1013B: A Very Cold (>T10) Brown Dwarf in a Binary System”, Liu et al., der udkommer i tidsskriftet Astrophysical Journal.

Forskerholdet består af Michael C. Liu (Institute for Astronomy [IfA], University of Hawaii, USA), Philippe Delorme (Institut de planétologie et d’astrophysique de Grenoble, CNRS/Université Joseph Fourier, Frankrig [IPAG]), Trent J. Dupuy (Harvard-Smithsonian Center for Astrophysics, Cambridge, USA), Brendan P. Bowler (IfA), Loic Albert (Canada-France-Hawaii Telescope Corporation, Hawaii, USA), Etienne Artigau (Université de Montréal, Canada), Celine Reylé (Observatoire de Besançon, Frankrig), Thierry Forveille (IPAG) and Xavier Delfosse (IPAG).

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

Michael Liu
Institute for Astronomy, University of Hawaii
USA
Tel: +1 808 956 6666
E-mail: mliu@ifa.hawaii.edu

Philippe Delorme
Institut de planétologie et d’astrophysique de Grenoble
France
Tel: +33 4 76 63 58 30
E-mail: Philippe.Delorme@obs.ujf-grenoble.fr

Christian Veillet
Executive Director, CFHT, Hawaii
USA
Tel: +1 808 885 7944
E-mail: veillet@cfht.hawaii.edu

Richard Hook
ESO, La Silla, Paranal, E-ELT and Survey Telescopes Press 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 eso1110 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.:eso1110da
Navn:CFBDSIR 1458+10
Type:Milky Way : Star : Type : Brown Dwarf
Facility:CFHT, New Technology Telescope, Very Large Telescope, W. M. Keck Observatory
Instruments:SOFI, X-shooter
Science data:2011ApJ...740..108L

Billeder

The coolest pair of brown dwarfs
The coolest pair of brown dwarfs
tekst kun tilgængelig på engelsk
The brown dwarf binary CFBDSIR 1458+10
The brown dwarf binary CFBDSIR 1458+10
tekst kun tilgængelig på engelsk
Wide-field view of the sky around the brown dwarf binary CFBDSIR 1458+10
Wide-field view of the sky around the brown dwarf binary CFBDSIR 1458+10
tekst kun tilgængelig på engelsk

Videoer

Zooming in on the brown dwarf binary CFBDSIR 1458+10
Zooming in on the brown dwarf binary CFBDSIR 1458+10
tekst kun tilgængelig på engelsk

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