Meddelelse
Fremtids planetjagt ved Alpha Centauri
Der bliver en sjælden mulighed for at jage planeter ved Alpha Centauri A i 2018
20. oktober 2016
I 2028 bliver der en meget sjælden mulighed for at se efter planeter ved en af de nærmeste stjerner. Det år vil man nemlig kunne observere det, som kaldes en gravitationslinsning, har et hold franske astronomer beregnet. Forskerholdet ledes af Pierre Kervella fra CNRS/Universidad de Chile.
Ud fra både arkiverede data og nye observationer med en række ESO teleskoper [1] har forskerne med stor nøjagtighed beregnet hvordan stjerneparret Alpha Centauri A og B vil bevæge sig i forhold til hinanden og til os. Der vil frem til 2050 være en række tilfælde, hvor Alpha Centauri stjerneparret vil passere meget tæt forbi andre stjerner, som ser ud til at være tæt på dem på himlen, men som i virkeligheden er meget længere væk[2].
Selv om det i sig selv er spændende at kunne kigge ind i fremtiden og beregne stjernebevægelser med stor nøjagtighed, så er det ikke det, som er det virkeligt spændende ved de nye beregninger. Det rigtig spændende kommer ind, fordi beregningerne kan bruges til at lede efter hændelser med sekundære gravitationslinser. Fænomenet gravitationslinseeffekt (Gravitational lensing) opstår fordi et tungt objekt som for eksempel en stjerne forvrænger selve rummet omkring den. Lys fra et fjernt objekt, som passerer tæt forbi stjernen på vej til os på Jorden bliver derfor afbøjet af tyngdefeltet fra stjernen. Den nærmere stjerne fungerer som en linse for lyset fra det fjerne objekt. I helt ideelle tilfælde kan der dannes en Einstein ring, som er en lyscirkel omkring forgrundsstjernen. Forgrundsstjernens masse bestemmer hvor kraftig forvrængningen er, og derfor kan afvigelser fra den forventede form af gravitationslinsen bruges til at afgøre både om der er planeter omkring stjernen og hvor tunge de er.
En af de mest spændende forudberegnede hændelser i denne sammenhæng er i maj 2028, hvor den tungeste af de to stjerner i Alpha Centauri-parret, Alpha Centauri A passerer så tæt foran en fjern baggrundsstjerne - formentlig en rød kæmpestjerne - med kælenavnet S5, at der vil kunne dannes en einsteinring, som vil kunne observeres med ESOs teleskoper[3]. Det giver os en enestående mulighed for at se efter planeter og andre mindre objekter omkring en af de nærmeste stjerner. Det er særligt spændende i lyset af, at der for nyligt er opdaget en planet, Proxima b, ved den tredje stjerne i systemet; den, som hedder Proxima Centauri.
Noter
[1] Det er ekstremt svært at måle de virkelige bevægelser for de fleste stjerner, fordi de er så langt væk. Det kræver utroligt præcise målinger og langvarige observationer. Forskerholdet har brugt data fra 2007 indsamlet med New Technology Telescope (NTT) og nye observationer fra instrumentet NACO på Very Large Telescope (VLT). Ud over dette er der indsamlet data fra Atacama Large Millimeter/submillimeter Array (ALMA), som har givet meget præcise målinger af de indbyrdes positioner for A og B i stjerneparret Alpha Centauri.
[2] Alpha Centauri systemet befinder sig tæt på Mælkevejens plan, så derfor er der rigtig mange fjerne stjerner i området omkring dem. Det har givet gode muligheder for at finde baggrundsstjerner, som kan ligge næsten perfekt på linie med en af de to klare stjerner i parret.
[3] Hændelsen vil kunne ses med instrumentet GRAVITY på Very Large Telescope Interferometer (VLTI), Atacama Large Millimeter/submillimeter Array (ALMA), og det kommende European-Extremely Large Telescope (E-ELT), så der er en god mulighede for at kunne bestemme massen af en planet med stor nøjagtighed.
ALMA er et partnerskab imellem ESO, the U.S. National Science Foundation (NSF) og National Institutes of Natural Sciences (NINS) of Japan i samarbejde med Republikken Chile.
Flere oplysninger
Forskningsresultatet her er offentliggjort den 19. oktober 2016 i tidsskriftet Astronomy and Astrophysics (Kervella et al. 2016, A&A, 594, A107)
Forskerholdet består af: P. Kervella, CNRS UMI 3386, University of Chile og LESIA, Paris Observatory; F. Mignard, Côte d’Azur Observatory, Frankrig; A. Mérand, ESO; og F. Thévenin, Côte d’Azur Observatory, Frankrig.
Links
- forskningsartiklen: http://www.aanda.org/10.1051/0004-6361/201629201
Kontakter
Ole J. Knudsen, ESON-Danmark
Stellar Astrophysics Centre, Aarhus Universitet
Aarhus, Danmark
tlf 8715 5597, mobil 4059 4520
e-mail: eson-denmark@eso.org
Om meddelelsen
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