This blazing maelstrom is Thor’s Helmet, a cloud of interstellar gas and stellar entrails set alight by a hot, unstable star nearing the end of its days. In this image by astrophotographers Kim Quick and Terry Hancock, the color and structure of this emission nebula hint at its youth and unusual nature.
Thor’s Helmet gets its glow from the massive unstable star WR7, a so-called “Wolf-Rayet” star which ejects much of its gaseous outer layers into space at speeds of up to 2,000 km/s. The ejected material from the star runs into the slower-moving gas floating between the stars. The collision excites the surrounding gas and causes it to emit light.
Wolf-Rayet stars are massive, fast-burning, and short-lived stars on their way to exploding as a supernovae. This phase of the star’s life only lasts briefly, which means Wolf-Rayet stars are quite rare. Only 150 have been discovered in the Milky Way.
The interstellar gas in and around this nebula is chemically enriched by the entrails of the Wolf-Rayet star. The rich blue-green color of the nebula comes from ionized oxygen ejected by the star. The reddish-pink color comes from excited hydrogen gas from the star and in the interstellar medium.
The intricate detail and structure in Thor’s Helmet hints at the history and structure of this short-lived nebula. The bubble-like section may have been blown out during the star’s more sedate life on the main sequence. Additional sections are made from other molecular clouds entwined with the bubble.
Thor’s Helmet, which is more formally cataloged as NGC 2359, lies at a distance of about 12,000 light years and spans about 30 light years.
This massive and distant complex is visible in a small telescope in very dark sky, though it’s not an easy object to see. With a 5″ or 6″ scope at low magnification, and a nebula filter, sharp-eyed stargazers can see the brightest sections of Thor’s Helmet about 10º northeast of the Sirius, the brightest star in the sky. Follow a line from the stars ι (iota) Canis Majoris through γ (gamma) Canis Majoris a distance about half again as large as their separation.
The image at top was captured by Kim Quick over 17 nights between 12/28/14 and 2/15/15 from his backyard observatory in Florida under moderately-high light polluted sky conditions using a QSI 583 Mono CCD and Explorer Scientific ED 127 Refractor. It was processed and Calibrated in CCDStack and post-processed in CS3. Total integration time was 27.5 hours.
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