I stars are second-generation stars. Our solar system formed from a big gas cloud. Most of the gas fell into the center to form the Sun. For galaxies, the mass is more spread out but there is still a concentration of mass ending up at the center. A black hole with maybe a million solar masses of material.
All large galaxies appear to contain super-massive black holes.
Early in the life of galaxies, when there is still lots of loose gas and dust falling into the black hole, galaxies have super-bright centers and appear as quasars . Edwin Hubble did this by spotting Cepheid variables. Recent results suggest that our Galaxy is a barred spiral, type SBb. Previously thought to be Sb. Typically 90,000 LY in diameter.