An 8-inch telescope at medium magnification reveals a bright and distinct bright round core set within a surrounding film of glaucous light that exhibits a bare hint of spiral structure. But M51 does not appear to be solitary. Just off the main disk to the north we see a diffuse stellar point with flared regions of light on either side, like a bow tie. This is NGC 5195, a more distant companion galaxy. Some 400 million years ago, these two galaxies passed near each other. The resulting gravitational tug-of-war pulled one of M51's spiral arms "out of round," as well as disturbed the structure of the companion.

The Whirlpool Galaxy lies 23 million light-years away in the constellation Canes Venatici the Hunting Dogs. Images made with the Hubble Space Telescope indicate that the galaxy's massive center is about 80 light-years across and contains the mass of 40 million suns. The density of stars in this region is about 5,000 times higher than in the sun's neighborhood. The core itself contains about one million times the mass of the sun within a region less than five light-years across. This, plus a tangle of dust lanes over the nucleus, suggests the presence of a massive black hole.