Stjärnor på beställning
Ingen fara - ingenting blir attackerat av rymdlasrar i denna veckas bild, även om det kan se ut som om de fyra gula strecken har satt kurs mot galaxerna till höger. Dessa streck är i själva verket fyra artificiella stjärnor. När stjärnljus passerar genom vår oroliga atmosfär blir det suddigt, vilket förvränger stjärnorna på astronomiska bilder. Artificiella stjärnor gör det möjligt att korrigera för detta – men varför ser de ut som streck på denna bild snarare än ljuspunkter, och hur skapas de?
De artificiella stjärnorna på bilden uppstår med hjälp av laserstrålar som skjuts upp från ESO:s Very Large Telescope (VLT) i Chile. Varje stråle kommer från ett av VLT:s fyra enskilda teleskop. Själva laserstrålarna syns svagt nere till vänster; de sprids av atmosfären på vägen uppåt. Allt eftersom de rör sig uppåt blir atmosfären tunnare, och strålarna framstår som allt svagare. Men på 90 kilometers höjd når de ett skikt som är rikt på natriumatomer. Dessa atomer börjar lysa starkt när de exciteras av lasrarna.
Eftersom natriumatomerna är utspridda i ett skikt som är cirka 5–10 km tjockt ser de ut som streck när de fotograferas från sidan – precis som på den här bilden, tagen på 2,5 kilometers avstånd från teleskopen. Men sedda från teleskopen, varifrån lasrarna utgår, framstår strecken som punktformiga ljuskällor. Ett adaptivt optiksystem övervakar hur dessa artificiella punkter tindrar, och styr en tunn, flexibel spegel i teleskopet som ändrar form hundratals gånger per sekund. Detta gör i sin tur att det inkommande ljuset från det astronomiska objekt man studerar blir skarpt igen.
Målet i denna bild är det supermassiva svarta hålet i centrum av NGC 3227, en av galaxerna till höger i bilden. Detta är en aktiv galax, vars centrum lyser starkt på grund av att det svarta hålet drar till sig omgivande gas. ESO-astronomen James Leftley studerar ett flertal sådana galaxer med GRAVITY- och MATISSE-instrumenten vid VLT-interferometern (VLTI).
Denna anläggning kopplar samman alla fyra huvudteleskop så att de fungerar som ett enda gigantiskt teleskop med en diameter på upp till 130 meter. Anläggningen har nyligen uppgraderats genom projektet GRAVITY+, vilket innebar att lasrar installerades på alla VLT-teleskopen. Med hjälp av dessa lasrar kan VLTI och dess instrument korrigera för oskärpan i bilderna nästan var som helst på den södra stjärnhimlen genom att skapa artificiella stjärnor på beställning precis där de behövs.
Källa:ESO/A. Berdeu
Om bilden
| ID: | potw2644a |
| Språk: | sv |
| Typ: | Observation |
| Publiceringsdatum: | 2 november 2026 06:00 |
| Storlek: | 4096 x 2730 px |
Om objektet
| Namn: | Laser Guide Star, NGC 3227 |
| Typ: | Unspecified : Technology |
Bildformat
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