The fact that
several such pristine galaxies turn out to have a small, still - expanding
black hole at their core suggests that
black holes can grow to intermediate size without
mergers, but then need to pool their resources to get much bigger.
We'll see how the authors explored the ramifications of throwing
several unassociated
black hole (BH) «strangers» into the mix (it's complicated — accretion, three - body interactions, and more are at play in mediating
mergers), and what it could mean in the context of recent GW discoveries.