What characteristics do all galaxies share? What makes them different?
All galaxies contain groups of stars and other material held together by gravity.
Galaxies can contain anywhere between a few thousand and
Some galaxies (like our own Milky Way galaxy) have central black holes and some don't.
Galaxies can take a variety of shapes, e.g. spiral, barred-spiral, elliptical or irregular.
Galaxies differ in the range of ages and types of stars.