The Grand Whirlpool Galaxy, M51, and Its Companion

Galaxy Messier 51 (M51, also designated NGC 5194) is nicknamed the Whirlpool because of its prominent swirling structure. Its two curving arms, a hallmark of so-called grand-design spiral galaxies, are home to young stars, while its yellow core is where older stars reside. Many spiral galaxies possess numerous, loosely shaped arms, which make their spiral structure less pronounced. These arms are star-formation factories, compressing hydrogen gas and creating clusters of new stars. Some astronomers believe that the Whirlpool's arms are so prominent because of the effects of a close encounter with NGC 5195, the small, yellowish galaxy at the outermost tip of one of the Whirlpool's arms. At first glance, the compact galaxy appears to be tugging on the arm. Hubble's clear view, however, shows that NGC 5195 is passing behind the Whirlpool. The small galaxy has been gliding past M51 for hundreds of millions of years. For more information, please visit: hubblesite.org/image/1677