Can stellar physics explain GW231123?

GW231123 is the new record-holder gravitational-wave event in terms of the largest black-hole mass. The heavier black hole there has a mass of up to 160 solar masses and, if that’s not enough, it is also spinning very rapidly. Does that make sense? Black holes usually form from the collapse of stars, so in this quick-reaction study we asked whether stellar evolution alone can produce black holes like those in GW231123. The answer is yes—you don’t need to invoke anything else—but the catch is that the heavier black hole must come from a star that underwent the so-called photodisintegration instability (i.e., what people refer to as a black hole “beyond the gap”).

D. Croon, J. Sakstein, D. Gerosa.
arXiv:2508.10088 [astro-ph.HE].