## Wednesday, May 9, 2012

### Thor's Helmet

Continuing my chain of astronomical images, tonight I have an image of a beautiful nebula, NGC 2359, popularly known as Thor's Helmet after its shape.

 NGC 2359, "Thor's Helmet", in Canis Major. North is to the left in this image.
NGC 2359 is about 15,000 light-years away, and around 30 light-years in size. It's a rather unusual kind of planetary nebula. Most planetary nebulae (as discussed before) come about from stars roughly the size of the Sun, gently wafting out the outer layers of their atmospheres as they reach the end of their lives. NGC 2359, in contrast, has a rare kind of star known as a Wolf-Rayet star at its center. Wolf-Rayet stars are extremely massive stars (at least 20 times more massive than the Sun) that are vigorously blowing their outer layers off under their own massive power generation (remember my talk about the Eddington Limit from the Eta Carinae picture?). Out Sun typically loses $$10^{-14}$$ solar masses' worth of material each year; Wolf-Rayet stars typically lose $$10^{-5}$$, a billion-fold increase.

The complex shape of NGC 2359 may be the result of interactions between the central star's stellar wind and a nearby molecular cloud, a region of greater-than-average gas and dust density. It's a rather faint nebula, so I'm glad I was able to get as much of it as I did (and it still required some pretty good histogram stretching to be this bright). The colors, though, are roughly correct, as I used wide-band filters instead of narrow-band ones.