Black Holes, Galaxies & Stars

Now that much of the inferred population of the universe's black holes has been found the overall picture seems to be like this.

In their youth, galaxies form stars and black holes together as the primordial gas and subsequently added dust (you don't get dust until the first generation of supernovae have gone pop and spilled their heavier elements - "metals" in astronomical terminology). The black holes at the centres of galaxies grow until they become quasars and the intensity of their own radiation holds back the very material they need to grow further, which leads to the general observation that central black holes are typically about 0.2% of galaxy mass (I think that's the right figure).

[Side note - now we have found the hidden population of black holes, we can infer something about quasar structure by comparing the numbers we can see directly with those we see indirectly through the infra-red etc. from surrounding dust.]

If this picture is broadly correct, then there should be a typical upper mass-limit for organically grown black holes.

My conclusion from all this: central black holes of greater mass should be indicative of galactic mergers and the mass of such holes might even be a proxy for the number of mergers that have occurred in the course of a particular galaxy;s history (complicated of course by the original size of the galaxy cluster etc.). It is interesting to consider that, whilst the specifics would always remain vague (barring identification of specific sub-populations of stars by e.g. velocity, age, etc. - we can do this for the Milky Way, and have found the remnants of several mergers this way, but it becomes increasingly difficult the further away a target galaxy is), one might be able to infer something about the original sizes of clusters, super-clusters etc. in the early universe from present day observations; or, running the logic in reverse, the more we learn about early cosmological structure, the more we may be able to infer about the dynamics of galactic mergers.

Just a thought. Just more Stuff.