Overview

• The GW231123 signal, captured on November 23, 2023, marks the merger of ∼100 and ∼140 M☉ black holes into a 225 M☉ remnant.
• Both progenitor black holes spun near the theoretical limit allowed by general relativity and lie within the predicted 60–130 M☉ mass gap.
• Calibrated 0.1-second ringdown waveform data have been published through the Gravitational Wave Open Science Center for independent verification.
• Researchers are exploring hierarchical merger chains and active galactic nucleus environments to explain the unexpected component masses and rapid spins.
• Distance to GW231123 remains uncertain at 0.7–4.1 billion light-years, underscoring the challenge of measuring extreme, short-lived signals.