Whirlpool Galaxy

The Whirlpool Galaxy is one of the most photographed galaxies in the sky, notable for its grand spiral arms and its ongoing interaction with the smaller companion galaxy NGC 5195, visible at the top of most images as a yellowish knot connected by a luminous bridge.

The gravitational interaction between the two galaxies has triggered waves of star formation throughout M51’s spiral arms, evident as the brilliant blue star clusters and pink star-forming knots tracing the arms in Hubble imagery. The pink regions are emission nebulae — ionized hydrogen glowing around newly formed massive stars.

The dark dust lanes weaving through the arms create a striking contrast against the star-forming regions. Near the nucleus, these lanes resolve into a complex web of filaments, and the bright yellow-white core contains an older stellar population and, at its center, an active galactic nucleus hosting a supermassive black hole.

NGC 5195 is believed to have passed through M51’s disk twice in the last few hundred million years, each passage compressing gas clouds and triggering new waves of star formation.