Imaging Spotlight: Thor’s Helmet in Space

In Canis Major, nearly 12,000 light years from Earth, lies an emission nebula that always makes me think of a particular comic book character.  NGC 2359 is 30 light years across, and is colloquially known as Thor’s Helmet.

Image credit: J.A. Toala & M.A. Guerrero, IAA-CSIC / Y.-H. Chu, UIUC-ASIAA / R.A. Gruendl, UIUC / S. Mazlin, J. Harvey, D. Verschatse & R. Gilbert, SSRO-South / ESA.

The complex structure of Thor’s helmet consists of bubbles and filaments, and is due to a series of bursts from the massive star HD 56925.  This star is a rare Wolf-Rayet star, which consistently expels its outer layers of gas at high velocities, and is characterized by its very high temperature.

The blue bubble in the above image is a result of the XMM-Newton X-ray telescope.  The X-rays trace the hottest bubble of gas plasma in the nebula, reaching 2 million degrees as a result of the shock waves of stellar wind.  The rest of the image, the red and green filaments, result from optical measurements, tracing the glow of ionized Hydrogen and Oxygen.

As with most astronomical images, this view could not be seen with human eyes, as it combines different parts of the spectrum.  But at the same time, techniques in imaging can allow a human brain to study the interactions of the hot and cool gas to determine how the central star is behaving, and how the local interstellar medium is structured.

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