Closeup of the Whirlpool Galaxy, Messier 51

Taken in visible light, this image shows a magnified view of the magnificent spiral galaxy Messier 51 (M51), dubbed the Whirlpool Galaxy. It highlights the attributes of a typical spiral galaxy, including graceful, curving arms, pink star-forming regions, and brilliant blue strands of star clusters. M51, also known as NGC 5194, is engaged in a close encounter with a nearby galaxy, NGC 5195, outside the field of view of this image. The companion's gravitational pull triggers star formation in the main galaxy, as seen in the numerous, luminous clusters of young and energetic stars. The bright clusters are highlighted in red by their associated emission from glowing hydrogen gas. Along the spiral arms, dust "spurs" are seen branching out almost perpendicular to the main spiral arms. The large number and regularity of these features are not fully understood, suggesting that previous computer models of "two-arm" spiral galaxies are incomplete.