Pressemeddelelse

Første planet fundet om en sol-lignende stjerne i en stjernehob

seks års eftersøgning med HARPS finder tre nye planeter i Messier 67

15. januar 2014

Astronomer har benyttet ESO’s HARPS “planetjæger” i Chile, sammen med andre teleskoper over hele jorden, til at opdage tre planeter i omløb om stjerner i stjernehoben Messier 67. Selvom mere end tusinde planeter udenfor solsystemet nu er kendt, er kun en håndfuld af disse er fundet i stjernehobe. Det er bemærkelsesværdigt at en af disse nye exoplaneter er i omløb om en sjælden “sol-tvilling” — en stjerne der på næsten alle måder er identisk med Solen.

Det er på nuværende tidspunkt et velkendt faktum at planeter om stjerner udenfor Solsystemet er hyppigt forekommende. Disse exoplaneter er fundet i omløb om stjerner med meget forskellige aldre og kemisk sammensætning og de er fordelt over hele himlen. Men, indtil nu, er ganske få planeter blevet fundet i stjernehobe [1]. Dette er specielt underligt fordi de fleste stjerner vides at blive født i sådanne hobe. Astronomer har spekuleret på om der måske er noget anderledes ved planetdannelsesprocessen i stjernehobe hvilket kunne forklare den besynderlige mangel på planeter i stjernehobe.

Anna Brucalassi (Max Planck Institute for Extraterrestrial Physics, Garching, Germany), førsteforfatter af dette nye studie, og hendes gruppe ville vide mere. "I Messier 67 hoben har stjernerne alle omtrent den samme alder og sammensætning som Solen. Dette gør den til et perfekt laboratorium til at undersøge hvor mange planeter der dannes i sådan et tætpakket miljø, og om de dannes fortrinsvis omkring stjerner med lille eller med stor masse."

Gruppen benyttede HARPS planet-finder instrumentet på ESO’s 3.6 meter kikkert på La Silla Observatoriet. Disse resultater blev suppleret med observationer fra flere andre observatorier over hele jorden [2]. De fulgte omhyggeligt udvalgte stjerner i Messier 67 [3] over en seks års periode for at lede efter de små cykliske bevægelser af stjernerne imod og væk fra Jorden der vidner om tilstedeværelse af omkredsende planeter.

Hoben ligger i en afstand af ca. 2500 lysår fra os i stjernetegnet Krebsen og indeholder omkring 500 stjerner. Mange af disse stjerner er svagere end dem man normalt vælger når man søger efter exoplaneter, og forsøget på at finde det svage signal fra eventuelle planeter var på den yderste grænse af hvad der er muligt med HARPS.

Tre planeter blev opdaget — to i kredsløb om sol-lignende stjerner og en i kredsløb om en mere udviklet rød kæmpestjerne med større masse. De to første planeter har begge en masse på omkring en tredjedel af Jupiters masse, og kredser om deres værtsstjerne på henholdsvis syv og fem dage. Den tredje planet bruger 122 dage om et omløb og har en større masse end Jupiter [4].

Den første af disse planeter viste sig at være i omløb om en bemærkelsesværdig stjerne — det er en af de mest Sol-lignende stjerner der endnu er fundet og er næsten magen til Solen (see også eso1337) [5]. Det er den første Sol-tvilling i en hob om hvilken der er fundet en planet.

To af de tre planeter er “varme Jupitere” — planeter med en størrelse nogenlunde som Jupiter, men meget taettere paa deres forældrestjerner og derfor meget varmere. Alle tre er tættere på deres værtsstjerne end den “beboelige zone” hvor flydende vand kan eksistere.

"Disse nye resultater viser at planeter i åbne stjernehobe er omkring lige så almindelige som de er omkring isolerede stjerner — men de er ikke nemme at detektere," tilføjer Luca Pasquini (ESO, Garching, Germany), medforfatter på den nye artikel [6]. “De nye resultater er i modstrid med tidligere undersøgelser der ikke fandt planeter i hobe, men er i god overensstemmelse med andre nyere observationer. Vi fortsætter med at observere denne hob for at finde ud af hvilke forskelle der er på masse og kemisk sammensætning af stjerner med og uden planeter.”

Noter

[1] Star clusters come in two main types. Open clusters are groups of stars that have formed together from a single cloud of gas and dust in the recent past. They are mostly found in the spiral arms of a galaxy like the Milky Way. On the other hand globular clusters are much bigger spherical collections of much older stars that orbit around the centre of a galaxy. Despite careful searches, no planets have been found in a globular cluster and less than six in open clusters. Exoplanets have also been found in the past two years in the clusters NGC 6811 and Messier 44, and even more recently one has also been detected in the bright and nearby Hyades cluster.

[2] This work also used observations from the SOPHIE instrument at the Observatoire de Haute-Provence in France, the Swiss 1.2-metre Leonhard Euler Telescope at ESO's La Silla Observatory in Chile and the Hobby Eberly Telescope in Texas, USA.

[3] Most open clusters dissipate after a few tens of million years. However, clusters that form with a higher density of stars can stay together for much longer. Messier 67 is an example of such a long-lived older cluster and is one of the oldest and best-studied of such clusters close to the Earth.

[4] Mass estimates for planets observed using the radial velocity method are lower estimates: if the planet's orbit is highly inclined it could have a higher mass and create the same observed effects.

[5] Solar twins, solar analogues and solar-type stars are categories of stars according to their similarity to the Sun. Solar twins are the most similar to the Sun, as they have very similar masses, temperatures, and chemical abundances. Solar twins are very rare, but the other classes, where the similarity is less precise, are much more common.

[6] This detection rate of 3 planets in a sample of 88 stars in Messier 67 is close to the average frequency of planets around stars that are not members of clusters.

Mere information

This research was presented in a paper entitled “Three planetary companions around M67 stars“, by A. Brucalassi et al., to appear in the journal Astronomy & Astrophysics.

The team is composed of A. Brucalassi (Max-Planck-Institut für extraterrestrische Physik, Garching, Germany [MPE]; Sternwarte, Munich, Germany), L. Pasquini (ESO, Garching, Germany), R. Saglia (MPE; Sternwarte), M.T. Ruiz (Universidad de Chile, Santiago, Chile), P. Bonifacio (GEPI, Observatoire de Paris, CNRS, Univ. Paris Diderot, France), L. R. Bedin (INAF - Osservatorio Astronomico di Padova, Padova, Italy), K. Biazzo (INAF - Osservatorio Astronomico di Catania, Catania, Italy), C. Melo (ESO, Santiago, Chile), C. Lovis (Observatoire de Geneve, Switzerland) and S. Randich (INAF - Osservatorio Astrofisico di Arcetri, Florence, Italy).

ESO er den mest fremtrædende internationale astronomi-organisation i Europa og verdens mest produktive astronomiske observatorium. ESO har i dag følgende 15 medlemslande: Belgien, Brasilien, Danmark, Finland, Frankrig, Holland, Italien, Portugal, Schweiz og Storbritannien, Spanien, Sverige, Tjekkiet, Tyskland og Østrig. ESOs aktiviteter er fokuseret på design, konstruktion og drift af jordbaserede observationsfaciliteter for at muliggøre vigtige videnskabelige opdagelser inden for astronomi. 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 samt to kortlægningsteleskoper. VISTA arbejder i infrarødt lys og er verdens største kortlægningsteleskop, mens VLT Survey Telescope (VST) er det største teleskop, der udelukkende er bygget til at kortlægge himlen 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 39 meter optisk/nær-infrarødt teleskop kaldet European Extremely Large Telescope (E-ELT), der vil blive "verdens største øje mod himlen".

Links

Kontakter

Anna Brucalassi
Max Planck Institut for Extraterrestrial Physics
Garching, Germany
Tel: +49 89 30000 3022
E-mail: abrucala@mpe.mpg.de

Luca Pasquini
ESO
Garching, Germany
Tel: +49 89 3200 6792
E-mail: lpasquin@eso.org

Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Mobil: +49 151 1537 3591
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 eso1402 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.:eso1402da
Navn:Messier 67
Type:Milky Way : Star : Grouping : Cluster : Open
Facility:ESO 3.6-metre telescope
Instruments:HARPS
Science data:2014A&A...561L...9B

Billeder

Kunstners forestilling af en exoplanet fundet om en sol-lignende stjerne i stjernehoben Messier 67
Kunstners forestilling af en exoplanet fundet om en sol-lignende stjerne i stjernehoben Messier 67
Stjernehoben Messier 67 i stjernebilledet Krabben
Stjernehoben Messier 67 i stjernebilledet Krabben
Vidvinkel billedet af stjernehoben Messier 67
Vidvinkel billedet af stjernehoben Messier 67

Videoer

ESOcast 62: Three planets found in star cluster
ESOcast 62: Three planets found in star cluster
tekst kun tilgængelig på engelsk
Zooming in on the star cluster Messier 67
Zooming in on the star cluster Messier 67
tekst kun tilgængelig på engelsk
Flying through the star cluster Messier 67
Flying through the star cluster Messier 67
tekst kun tilgængelig på engelsk
Flying through the star cluster Messier 67 (annotated)
Flying through the star cluster Messier 67 (annotated)
tekst kun tilgængelig på engelsk
Panning across the star cluster Messier 67
Panning across the star cluster Messier 67
tekst kun tilgængelig på engelsk

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