(I'm astrophysicist Neil deGrasse Tyson.) Some with billions, others with trilions of stars, these are the fundamental building blocks of visble matter in the universe; they come in many varieties including spiral, irregular & elliptical
... Irregular Island, 
Cosmos Esf, Hubble Spots, Islands, Nebula, Spaces, Photos ... shape  unlike 
the more common spiral or elliptical galaxies  with knots of blue star formation.