Image of the Day: Ghostly Fire of the Medusa Nebula


The red serpentine filaments of glowing gas four light years across give this nebula its name. Also known as Abell 21, the Medusa is an old planetary nebula some 1,500 light-years away in the constellation Gemini. Like its mythological namesake, the nebula is associated with a dramatic violent transformation. The planetary nebula phase represents a final stage in the evolution of low mass stars like the sun, as they transform themselves from red giants to hot white dwarf stars and in the process shrug off their outer layers. Ultraviolet radiation from the hot star powers the nebular glow. The Medusa's transforming hot central star is visible in the detailed color image as the small blue star within the upper half of the overall bright crescent shape. Fainter filaments clearly extend above and to the left of the bright crescent region. 

Image credits: NASA/Hubble


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