Whirlpool Galaxy M51 is a Real Beauty

The Whirlpool Galaxy is one of astronomy's galactic darlings. Located only about 30 million light-years away (although this is still difficult to determine exactly) in the constellation Canes Venatici (the Hunting Dogs), the Whirlpool's beautiful face-on view and closeness to Earth allow astronomers to study a classic spiral galaxy's structure and star-forming processes.

With 60 thousand light years across, Messier M51, also known as NGC 5194, is one of the brightest and most picturesque galaxies on the sky. The first image is a digital combination of a ground-based image from the 0.9-meter telescope at Kitt Peak National Observatory and a space-based image from the Hubble Space Telescope highlighting sharp features normally too red to be seen.

M51 is so bright (for an extra-galactic object) that it is even visible through binoculars under dark sky conditions and can be resolved in detail with modern amateur telescopes. When seen through a 100 mm telescope the basic outlines of M51 (limited to 5x6') and its companion galaxy are visible.

This second image is the sharpest-ever image, taken in January 2005 with the Advanced Camera for Surveys aboard the NASA/ESA Hubble Space Telescope. It illustrates a spiral galaxy's grand design, with the spiral arms and dust clouds which are the birth sites of massive and luminous stars, to its yellowish central core, a home of older stars.

Many spiral galaxies possess numerous, loosely shaped arms that make their spiral structure less pronounced. These arms serve an important purpose in spiral galaxies. They are star-formation factories, compressing hydrogen gas and creating clusters of new stars. In the Whirlpool, the assembly line begins with the dark clouds of gas on the inner edge, then moves to bright pink star-forming regions, and ends with the brilliant blue star clusters along the outer edge.

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 the Whirlpool for hundreds of millions of years.