Active galaxies Galaxies are not stable, on the contrary: they grow and move, that is, they are active. Some more and others not so much. Almost all galaxies have a black hole in their center. While the black hole is active, it catches and engulfs all the matter around it, like a whirlpool. When the black hole of an active galaxy no longer has the capacity to swallow more, matter continues to revolve around it, but it no longer falls inside.