SPIRAL galaxies consist of
a nucleus, a disk, a halo, and spiral arms. Interstellar material such as gas and dust
are found in and near the spiral arm structure in the disk of the
galaxy. The spiral arms are sites of star formation,
which typically contain bright stars and OB (star) associations,
which make the spiral arm structure
easily discernible. Our own Galaxy is a spiral. Spirals that are face-on towards us appear like
giant pinwheels, like NGC 2997 below, © Anglo-Australian Observatory.
ELLIPTICAL galaxies as their name suggests, have elliptical or
spheroidal like shapes. The majority of their stars are old (K and M
giants), and they have much less dust and gas
than the spirals. Messier 87, a giant elliptical in the Virgo cluster
is shown below, © Anglo-Australian Observatory.
IRREGULAR galaxies have little discernible shape and can
be quite complex in their appearence. They usually have numerous
star formation sites (HII regions) and can have varying amounts of
dust. The Large Magellanic Cloud, the nearest large galaxy to the Milky Way
is an irregular and is shown below, © Anglo-Australian Observatory.
