“One has to be an optimist; one has to hope that somewhere there’ll be new measurements to be made and that they will open up new vistas for us theorists to play with.” –Jim Peebles
It was one of the most hotly contested questions for decades: we first expected and then found supermassive black holes at the centers of practically all large galaxies. But how did they get there?
In particular, you could imagine it happening either way: either there was this top-down scenario, where large-scale structures formed first and fragmented into galaxies, forming black holes at their centers afterwards, or a bottom-up scenario, where small-scale structures dominate at the beginning, and larger ones only form later from the merger of these earlier, little ones.
As it turns out, both of these play a role in our Universe, but as far as the question of what came first, black holes or galaxies, only one answer can be right. Go find out the whole story here!