Whirlpool Galaxy Facts

The Whirlpool Galaxy is a familiar one to stargazers and among the many close galaxy neighbors to our own Milky Way. Because of its shape, it was the first galaxy to be classified as a spiral by astronomers. Today, it interests astronomers due to its spiral structure and the interaction it appears to be having with its near neighbor, M51b.



Galaxy Profile
Designation: M51, SA(s)bc pec
Type: Spiral
Distance from Milky Way: ~25 million light-years
Diameter: about 75 thousand light-years across
Mass: ~160 billion suns
Number of Stars: > 100 billion

Facts About The Whirlpool Galaxy

• The Whirlpool Galaxy was first discovered in 1773 by Charles Messier, who was charting the             skies looking for objects that might be confused with comets.

• In 1845, astronomer William Parsons observed the galaxy pair with his telescope at Birr Castle,           Ireland, and found the spiral structure of the Whirlpool.

• The Whirlpool and its companion, M51b have already passed by or through each other once as           they dance through a cosmic merger. The smaller galaxy has been severely disrupted by the                 encounter, and the Whirlpool’s spiral arms are distorted.

• The Whirlpool Galaxy is undergoing huge bursts of starbirth due to its ongoing encounter with           its smaller companion galaxy.

• The whirlpool, like many other galaxies, has a supermassive black hole at its heart, surrounded           by rings of dust. The core of the galaxy is quite quite active — making the Whirlpool what                 astronomers call a “Seyfert galaxy”.

• The Whirlpool’s companion, called M51b, is a dwarf galaxy. Because it is being torn apart by             the ongoing interaction, it cannot be easily classified. Its current appearance makes it look like             an irregular galaxy.

• A bridge of gas and dust ties the two galaxies together as they merge.