The Spiral Galaxy Messier 81 the Spiral Galaxy Messier 81

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The Spiral Galaxy Messier 81 The Spiral Galaxy Messier 81 The magnificent, dusty, star-studded bulge are the grand spiral arms which and comparing them to the distribution arms of a nearby spiral galaxy, Messier are very rich in infrared-emitting dust. of gas and dust, astronomers can 81, are illuminated in this image from This dust is bathed in ultraviolet and learn more about the conditions and NASA's Spitzer Space Telescope. visible light from the surrounding processes needed for star formation. Located in the northern constellation of stars. When the dust absorbs this light, The white stars scattered throughout Ursa Major (which also includes the it heats up and then releases this heat the image are foreground stars within Big Dipper), this galaxy is easily visible as infrared light. By detecting these our own Milky Way galaxy. through binoculars or a small telescope. dust particles, composed of silicates Located 12 million light-years away, (which are chemically similar to beach This Spitzer Space Telescope image M81 is one of the closest spiral galaxies sand) and polycyclic aromatic hydro- was obtained using instruments that to our Milky Way galaxy. carbons (which are organic molecules), are sensitive to invisible infrared light astronomers can trace the distribution at wavelengths about ten times longer Because it is so close compared to most of gas and dust in the galaxy. This gas than visible light. It is a composite other galaxies, M81 gives astronomers and dust provides the raw materials made using both Spitzer's multiband an opportunity to study the properties from which future stars will form. imaging photometer and its infrared of a spiral galaxy in great detail. Using array camera. Infrared emission at a data from highly sensitive infrared The infrared-bright clumpy knots wavelength of 24 microns (red) from instruments, this Spitzer image shows within the spiral arms show the places the photometer is combined with us old stars, interstellar dust heated by where massive stars are being born in infrared camera data at 5.8-8.0 microns newly-formed stars, and embedded giant molecular clouds. The greenish (green), and 3.6-4.5 microns (blue). A sites of star formation within this areas are regions dominated by the micron is one millionth of a meter. galaxy. Detailed study of infrared infrared light radiated by hot dust that images of M81 have allowed has been heated by nearby bright stars. astronomers to also measure the Reddish regions in the spiral arms galaxy's overall dust content, as well as represent the places where dust is the rate at which new stars are being heated by the most luminous young formed. stars. The image shows the power of Spitzer to explore regions unseen in The bluish-white central bulge of the visible light and to study star formation galaxy contains older stars and only a on a galactic scale. By studying the little dust. Winding outward from the locations of these star-forming regions http://www.spitzer.caltech.edu/ To learn more about infrared astronomy, visit http://coolcosmos.ipac.caltech.edu/.

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