The Whirlpool Galaxy is also known as Messier 51a, and it’s one of the most familiar galaxies. If you’ve seen a picture of a galaxy captured by the Hubble Space Telescope, chances are you were looking at the Whirlpool Galaxy. That’s because this galaxy, located about 23 million light-years away in the constellation Canes Venatici, is aligned almost perfect face on. We have beautiful view of the Whirlpool Galaxy’s entire structure, from its spiral arms to its dense galactic core.
The Whirlpool Galaxy is fascinating for another reason as well. It has a companion galaxy to one side called NGC 5195. The two galaxies interact through gravity, and this gives astronomers a chance to study what happens when galaxies collide.
Astronomers have calculated that the Whirlpool Galaxy measures about 38,000 light-years across, with a mass of about 160 million times the mass of the Sun. This makes the galaxy smaller and less massive than our own Milky Way.
You can see the Whirlpool galaxy with a good pair of binoculars, or a small backyard telescope; although, you’ll want a bigger telescope to see the spiral structure and detect the companion galaxy NGC 5195. To find the Whirlpool Galaxy, located the easternmost star in the Big Dipper. Then go about 3.5 degrees to the southeast. On a dark night you should be able to see a fuzzy spot where the galaxy is.
Astronomers think that NGC 5195 first passed through the main disk of the Whirlpool Galaxy about 500 to 600 million years ago, and then made another disk crossing about 50 to 100 million years ago.
We have written many articles about galaxies for Universe Today. Here’s a link to a photograph of the Whirlpool Galaxy captured by amateur astronomer Robert Gendler.
We have also recorded an episode of Astronomy Cast about galaxies – Episode 97: Galaxies.