Central black holes in galaxies grow. 10 14-20 years . Binary stars spiral together and merge. Collisions between white dwarfs produce supernovae. Collisions between brown dwarfs produce low mass stars.
Typical galaxies shine with one solar luminosity.
The only luminosity in the universe comes from white dwarfs absorbing dark matter. White dwarfs glow at a temperature of 64K. 10 33-37 years. The end of matter. White dwarfs glow with an luminosity of 400 Watts. The Black Hole era .