Spiral galaxy. M51 spiral galaxy, also known as the "Whirlpool Galaxy", is 20 million light years away in constellation Canes Venatici. M51 has a diameter of around 65,000 light years and a mass of about 50,000 million solar masses about half the values of our own Milky Way. This image shows the variation in star colors in the galaxies. The nuclei contain mainly older, yellower stars while the spiral arms have more hot young blue stars. The galaxies are linked by a thin bridge of gas and dust which NGC 5195 has pulled from the larger galaxy by gravitational attraction.