NASA Astronomy Picture of the Day Collection

M81: A Bulging Spiral Galaxy

Few stars are still forming in the old giant spiral galaxy M81. The blue regions in this picture [ http://fondue.gsfc.…] - representing ultraviolet light [ http://antwrp.gsfc.…] - highlight regions of bright young stars and star formation and appear rare than in M74 [ http://antwrp.gsfc.…] and M33 [ http://antwrp.gsfc.…]. The red regions - representing the visible light - show a large population of older, less massive stars. M81 [ http://seds.lpl.ari…] is therefore classified as spiral galaxy [ http://antwrp.gsfc.…] type "Sab" on the Hubble Sequence of Galaxies [ http://dept.physics…]. One distinguishing feature of these types of galaxies is the relatively large central bulge surrounding the center of the galaxy. A massive density wave [ http://adsabs.harva…] circulates around the center of spiral galaxies. It is not well understood why the bulge of M81 [ http://crux.astr.ua…] glows as bright as it does in ultraviolet light. Speculation includes that this may be due to hot evolved stars such as those found in the ancient globular cluster Omega Centauri [ http://antwrp.gsfc.…].

NASA [ http://www.nasa.gov/], UIT [ http://fondue.gsfc.…]

Arizona

M81

M33

M74

Goddard Space Flight Center (GSFC)

Crux

Visible Light

spiral galaxy

http://antwrp.gsfc.…

SPD-APOD-ap960713