The Anatomy of Galaxies Following on from my post about the
Hubble diagram, I thought I’d mention a bit about the main types
of galaxies that are out there. Galaxies come in three basic
types: spirals, ellipticals and irregulars. Each of these three
broad morphologies of galaxy tells us a little about what is
going on inside the galaxy itself. They are all structured
differently. The spiral arms of a galaxy contain most of the
interstellar medium – dust and other material between stars –
within a galaxy. It is in the spiral arms that new stars are
forming, hence their usually bright, blueish or white colour.
Spirals are made of about 10-20% dust and gas. This is the
source material for the stars that are forming within the spiral
arms. It is the dust that obscures background light to create
the dark lanes you see in spiral galaxies. You can the arms and
the dust lanes very well in this artistic impression of our own
galaxy, the Milky Way from Nick Risinger / NASA. The central
bulge of spiral galaxy contains o