NGC 2359 Thor's Helmet

 Image Credit: Fred Calvert / Adam Block / KPNO /AURA / NSF


NGC 2359 “Thor’s Helmet” is a nebula that is the result of extensive mass loss from an evolved massive bright star that is located slightly left from the image center.

This star, HD56925 is referred to as a Wolf-Rayet star, is a massive blue giant blowing off massive amounts of dust and gases at millions of kilometers per hour.

Only about 300 Wolf-Rayet stars are known to exist.

Wolf-Rayet stars (named for their discoverers) are very large, massive stars (stars which are about 20 times bigger than the sun) nearly at the end of their stellar lives. As these stars age, material which the stars have cooked up in their central nuclear furnaces (like carbon and oxygen) gradually reach the surface of the star. When enough material reaches the surface, it absorbs so much of the intense light from the star that an enormously strong wind starts to blow from the star's surface. This wind becomes so thick that it totally obscures the star - so when we look at a Wolf-Rayet star, we're really just seeing this thick wind. The amount of material which the wind carries away is very large - typically, a mass equivalent to that of the entire earth is lost from the star each year. The mass loss is so large that it significantly shortens the star's life, and as you can imagine has important effects on the space surrounding the star too. We think that very massive stars become Wolf-Rayet stars just before they explode as supernova though no one has yet seen such a star explode. (Dr. Michael Corcoran, NASA)

The bubble-like emission nebula is approximately 30 light-years across and located in the Constellation Canis Major at a distance of about 15,000 light-years.





20" RC Optics Systems Telescope @ F 5.5 on a Paramount ME Robotic Mount SBIG ST10XME w Color Filter Wheel & AO-7 Adaptive Optics

Exposure Data:

Part of the Luminance data (30 min) was lost due to a filter wheel malfunction. Major work in both MaxIM DL and Photoshop was needed to produce the above image which is not as sharp as other in this run.


Luminance = 60 minutes binned 1 X 1

Red = 10 minutes binned 2 X 2

Green = 10 minutes binned 2 X 2                                

Blue = 10 minutes binned 2 X 2


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