Meddelelse
Supernovaeksplosion på replay. Nye muligheder med MUSE
25. november 2015
Astronomer forudser en begivenhed langt ude i Universet før den faktisk kan observeres. Det er MUSE-instrumentet på ESOs Very Large Telescope (VLT) på Paranalobservatoriet, som har gjort det muligt at teste teorierne for, hvordan tunge galaksehobe opfører sig. MUSE står for Multi Unit Spectroscopic Explorer.
På billeder af galaksehoben MACS J1149+2223, optaget med NASA/ESA Hubble Space Telescope i november 2014, ser man en fjern stjerne eksplodere - en supernova - på en måde, som aldrig før er set. Supernovaen har fået navnet Refsdal[1], og den er speciel fordi den er observeret som fire adskilte pletter på himlen, dannet via den proces, som kaldes gravitationslinsning. Billederne danner et næsten perfekt Einsteinkors omkring en af galakserne i hoben
Gravitationslinsning er en konsekvens af Einsteins generelle relativitetsteori. Den artikel, som beskrev de grundlæggende ligninger for denne helt epokegørende teori om tyngdekraften blev offentliggjort den 25. november 1915; altså for hundrede år siden.
Observationer af MACS J1149+2223 med MUSE i starten af 2015 har gjort det muligt at bestemme præcise afstande til galakserne i hoben. Ud fra det, har astronomerne kunnet modellere stoffordelingen inde i den enorme galaksehob meget mere præcist end tidligere. Med disse gode oplysninger i hånden har det været muligt at forudsige, hvor og hvornår der vil dukke et andet billede af den fjerne supernova op. I praksis vil det give astronomerne mulighed for at gense udviklingen af hele eksplosionens forløb, ligesom gentagelsen af målscoringen på den store skærm på stadion - men her i langt større skala.
Sådan et replay er muligt fordi lyset fra supernovaen bevæger sig ad forskellige veje frem til Jorden. Vejene har forskellig længde, så lyset fra eksplosionen dukker op på forskellige tider og på forskellige steder på himlen.
Ved at kombinere alle tilgængelige data fra MUSE med Hubbleobservationer har et hold astronomer fra Dark Cosmology Centre ved Niels Bohr Institutet i København, ledet af Claudio Grillo forudset, at et replay vil udspille sig med kraftigst lysstyrke imellem marts og juni 2016. Det første lys fra supernovaen skulle nå os før 2015 rinder ud. Ikke nok med at forudsigelsen fortæller hvor og hvornår supernovaen bliver synlig igen, men den antyder også hvor klar den vil komme til at se ud.
Nu bliver Hubbleteleskopet med regelmæssige mellemrum rettet imod hoben i håb om at fange denne enestående begivenhed. Lykkes det, får vi en meget præcis mulighed for at teste astronomernes modeller.
Atter en gang ser vi med disse observationer hvor vigtig en rolle MUSE og VLT spiller i udforskningen af det fjerne Univers, og også hvor fin en synergi der er imellem Hubble og jordbaserede observatorier.
Note
[1] Den er opkaldt efter den afdøde norske astronom Sjur Refsdal, som var pioner indenfor studiet af gravitationslinser.
Kontakter
Ole J. Knudsen
ESON-Danmark
Stellar Astrophysics Centre, Aarhus Universitet
tlf 8715 5597
mobil 4059 4520
e-mail eson-denmark@eso.org
Om meddelelsen
| Id: | ann15088 |
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