A cosmic bubble fit for a Viking god of thunder

Amateur astronomer Brigitte Bailleul won herself a chance to observe a target of her choice at Very Large Telescope (VLT) in Chile – an observatory that most professional astronomers only wish they could use. Brigitte was given the chance to observe any target of her choosing. And man, did she chose well:

Thor's Helmet Nebula
Thor’s Helmet as imaged by the European Southern Observatory’s (ESO) Very Large Telescope (VLT) as part of ESO’s 50th anniversary. Credit: ESO/B. Bailleul

Holy Helm of the Gods! This is the Thor’s Helmet Nebula. It’s a giant bubble of glowing gas being blown by the hot, massive star at the center, a special type of star called a Wolf-Rayet star. Wolf-Rayet stars are giant stars that are in a brief period of their lives where they have evolved from the day-to-day hydrogen fusing stage of their lives but not yet ready to explode in a supernova.

The star is losing mass somewhere between 10-6 and 10-5 of a solar mass per year. By comparison, our Sun loses about 10-14 solar masses per year in its solar wind, so this star is losing quite a lot of mass at a fairly high rate. This forms a powerful wind that “inflates” the bubble as it expands outward from the star. The bubble is huge, about 30 light-years across. But the star is so hot and energetic it still ionizes the gas, causing it to glow.

It gets better – the giant full resolution (424×3437) image reveals a lot of detail. You’ll definitely want to click that link, even if you have to go grab a cup of tea while it downloads. The swirls and arcs in the expanding bubble shows wave after wave of powerful winds being blown out by the central star, slamming into cooler, darker gas and dust in the surrounding nebula. Near the edges of the image are the “wings” of the nebula that extent well outside of VLT’s view. This wide-field view from the Digital Sky Survey shows its resemblance to Thor’s helmet:

This wide-field view shows the rich region of sky around the Thor’s Helmet Nebula (NGC 2359) in the constellation of Canis Major (The Great Dog). Image credit: ESO/Digitized Sky Survey 2. Acknowledgement: Davide De Martin

Thor blows a mighty wind, indeed!