Why do many galaxies appear as spirals [ http://www.seds.org…]? A striking example is M101, shown above [ http://www.cfht.haw…], whose relatively close distance of about 22 million light years allow it to be studied in some detail. Recent evidence [ http://adsabs.harva…] indicates that a close gravitational interaction with a neighboring galaxy created waves of high mass [ http://fuse.pha.jhu…] and condensed gas which continue to orbit the galaxy center. These waves [ http://home.cc.uman…] compress existing gas and cause star formation. One result is that M101 [ http://www.seds.org…], also called the Pinwheel Galaxy [ http://www.noao.edu…], has several extremely bright star-forming regions [ http://antwrp.gsfc.…] (called HII regions [ http://skyserver.fn…]) spread across its spiral arms. M101 [ http://www.astr.ua.…] is so large that its immense gravity distorts smaller nearby galaxies.
Explanation
Why do many galaxies appear as spirals [ http://www.seds.org…]? A striking example is M101, shown above [ http://www.cfht.haw…], whose relatively close distance of about 22 million light years allow it to be studied in some detail. Recent evidence [ http://adsabs.harva…] indicates that a close gravitational interaction with a neighboring galaxy created waves of high mass [ http://fuse.pha.jhu…] and condensed gas which continue to orbit the galaxy center. These waves [ http://home.cc.uman…] compress existing gas and cause star formation. One result is that M101 [ http://www.seds.org…], also called the Pinwheel Galaxy [ http://www.noao.edu…], has several extremely bright star-forming regions [ http://antwrp.gsfc.…] (called HII regions [ http://skyserver.fn…]) spread across its spiral arms. M101 [ http://www.astr.ua.…] is so large that its immense gravity distorts smaller nearby galaxies.
