oh yeah just watched about super massive black holes.

basically dust eventually (by something unknown) starts to rotate... after that step it creates a massively dense center with a gravitational pull that is so great that it begins to suck in everything around it in. so with this gravitational pull it accelerates the gases and rock and anything else around and therefore creates so much friction that it super heats the area immediately surrounding the center or "the singularity" and therefore creates immense light. with this process it creates stars from the gravitational pull making the dust clumps around the hole super condense and explode. so basically every galaxy had a black hole that birthed the entire galaxy... even ours.

they found the relationship by measuring the speed of rotation of the outermost stars in the galaxies compared to the size of the black hole. they found that the larger the hole, the faster the outermost stars were, which means that at some point in time they were directly related.