I've been reading some books on Galactic Structures and Galactic Evolutions, evidence from rotation curves of stars near the centre of our Milky Way and also M31 suggest that there is a blackhole in the centre. But is this true for all galaxies regardless of their Hubble Type? is there a galaxy that does not have a blackhole at its centre?? What type of evidences beside rotation curves suggest that there is a blackhole?? X-ray emissions from its accretio disk?