The Whirlpool Galaxy (M51) and Companion Galaxy

The large Whirlpool Galaxy (left) is known for its sharply defined spiral arms. Their prominence could be the result of the Whirlpool's gravitational tug-of-war with its smaller companion galaxy (right).

Release Date: April 25, 2005

Credit: NASAESA, S. Beckwith (STScI), and the Hubble Heritage Team (STScI/AURA)