It's easy to see why astronomers call this interstellar object "Thor's Helmet." It even has the little thunder-god wings, and you expect a cosmic voice to shout "I say thee nay!" from its center. But it's actually a 30-light-year bubble, blown by the wind from a huge central star, which scientists think is on the brink of going nova. Image by Robert Gendler. [NASA's Astronomy Picture of the Day]
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"Thor's Helmet" sounds like a brand of condoms.