The nucleus has a non-thermal spectrum. The spectral emission lines are very broad. The nucleus is often bright in the infrared. The nucleus often emits strong radio signals. There is often a giant, dominant elliptical at the center of galaxy clusters.
Galaxy clusters are strong sources of neutrinos.
There is very little gas in galaxy clusters. The galaxies are heavily obscured by dust. There are many clusters of galaxies near us in space, but nothing beyond. Tomorrow a group of astronomers will announce that the value of is exactly equal to one. The steady state theory will need to be revived as an alternative to the Big Bang theory.