Whirlpool Galaxy, M51, in Visible and Infrared Light (2003/2004)

NASA's Spitzer Space Telescope captured the infrared image (at right) of the "Whirlpool Galaxy," revealing strange structures bridging the gaps between the dust-rich spiral arms, and tracing the dust, gas and stellar populations in both the bright spiral galaxy and its companion.

The Spitzer image is a four-color composite of invisible infrared light, showing emissions from wavelengths of 3.6 microns (blue), 4.5 microns (green), 5.8 microns (orange) and 8.0 microns (red). These wavelengths are roughly 10 times longer than those seen by the human eye.

The visible light image (at left) comes from the Kitt Peak National Observatory 2.1m telescope, and has the same orientation and size as the Spitzer infrared image, measuring 9.9 by 13.7 arcminutes (north up). Also a four-color composite, the visible light image shows emissions from 0.4 to 0.7 microns, including the H-alpha nebular feature (red in the image).

The light seen in the images originates from very different sources. At shorter wavelengths (in the visible bands, and in the infrared from 3.6 to 4.5 microns), the light comes mainly from stars. This starlight fades at longer wavelengths (5.8 to 8.0 microns), where we see the glow from clouds of interstellar dust. This dust consists mainly of a variety of carbon-based organic molecules known collectively as polycyclic aromatic hydrocarbons. Wherever these compounds are found, there will also be dust granules and gas, which provide a reservoir of raw materials for future star formation.

The Spitzer image was captured on 18 and 22 May 2004; the Kitt Peak image was captured on 28--29 Marck 2003.

Credit: NASA/JPL-Caltech/R. Kennicutt (Univ. of Arizona)/DSS [source].

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