This, combined with the randomization in orbits, can turn the galaxy into an elliptical. Collisions may explain why the dense central parts of clusters have very few spiral galaxies, and often 1 or 2 giant Cd galaxies. A spiral can probably absorb much smaller galaxies without changing much. The Milky Way will probably tidally tear apart the Magellenic Clouds and absorb them. The Andromeda Galaxy may have already done the same thing.
Many galaxies have unusual activity in their cores.
Seyfert galaxies are spirals with very strong emission line sources in their cores. The brightest cores can be 10 times the luminosity of the Milky Way. Seyfert luminosities often vary on periods of a fraction of a year. Some galaxies have very strong radio sources, either right in their cores, or in vast lobes and jets coming from the core. The lobes can be much larger than the galaxy itself.