In a paper published in The Astrophysical Journal Letters, the international LIGO-Virgo-KAGRA Collaboration reports on the detection of two gravitational wave events in October and November of 2024 with unusual black hole spins. This observation adds an important new piece to our understanding of the most elusive phenomena in the universe.
Very cool paper and I don’t want to be the Internet Armchair Astrophysicist, but doesn’t the fact that we’ve already observed a merger show that second-generation black holes are a thing? Or is this evidence that BH mergers (and therefore second-gen BHs) might be more common than we previously thought?
We had seen merges of two first generation black holes but never of this type which would have had at least one other merger prior to this merger detected (either four merged into two merged into one or some other configuration like that). That’s what they mean by hierarchical mergers.
Ah, so the differing spin (and mass) of the merging black holes they just detected indicate that at least one of them was already a second generation black hole, and is evidence for multi-generation hierarchical mergers. That makes sense.
“Second-generation” isnt referring to whether it merged before, it’s referring to (and this might be a not fully correct analysis either) whether conservation of angular momentum got fucked up, like when you’re playing Mario Kart and you get smacked so many times that you get confused and start driving in the wrong direction.
It absolutely does mean having merged in the past. That’s why the rotation is different.
That Mario Kart simile may be accurate, but it also got my emotions going in all sorts of directions.