Alternate Names

NGC 5194/5195, Whirlpool Galaxy

Type

Supermassive

Location

in the constellation Canes Venatici, beneath the Big Dipper

Finder Chart

Distance

27 million light-years

Mass

1 million times the mass of the Sun

Size

Diameter of 4 million miles (6 million km), about four times the diameter of the Sun.

Discovery Methods

• Detection of an accretion disk

M51

One of the most beautiful of all galaxies is M51. It's nicknamed "the Whirlpool" because of its well-defined spiral arms. It actually consists of two galaxies -- the big spiral (NGC 5194), and a smaller galaxy (NGC 5195) that looks like it's being reeled in by the bigger one.

The smaller galaxy is actually moving away from the bigger one. As they move apart, their gravity is pulling out long streamers of stars that form a "bridge" between the two galaxies. The encounter has also ignited an intense outburst of starbirth in the larger galaxy. Since most of the new stars are born in the galaxy's spiral arms, they make M51's spiral structure particularly obvious.

In 1992, Hubble Space Telescope images revealed a dark "X" across the bright core of M51's larger galaxy. This X may be two disks of dust that encircle a black hole about one million times the mass of the Sun (about one-third as massive as the black hole at the heart of our own Milky Way galaxy). They form an X because we're viewing them edge-on (like viewing a Frisbee from the side instead of above). They are about 100 light-years wide, and hide the bright inner region of the disk where gas and dust are heated as they spiral in to the black hole.

References

Chandra X-Ray Observatory Fact Sheet

Hubble Space Telescope Discovers Dark ‘X' Across the Nucleus of M51

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This document was last modified: November 19, 2009.