On November 23, 2023, at 13:54:30 UTC, the LIGO-Virgo-KAGRA (LVK) collaboration detected GW231123, a gravitational-wave signal likely caused by the merger of two black holes with the highest combined mass the LVK collaboration has ever observed. These black holes would have been spinning incredibly fast, and their individual masses appear to fall into a range that challenges existing theories about how massive stars evolve and end their lives.
[Image credit: Simona J. Miller / California Institute of Technology]