Pinwheel galaxy (M101)

Galaxies

It is estimated that there are between 200 billion and 2 trillion galaxies in the universe. Each galaxy may contain several hundreds of thousands of stars. It is for example estimated that our galaxy, the Milky Way has over 100 billion stars. Galaxies are classified either as ellipitcal, spiral or irregular. Galaxies are made of stars, stellar remnants, interstellar gas, dust and dark matter.