A recent study suggests that the gravitational wave signal GW231123, detected on November 23, 2023, by the Laser Interferometer Gravitational-Wave Observatory (LIGO), might be the result of a gravitational lensing effect rather than the merger of two extremely massive black holes. This hypothesis challenges previous assumptions about the black holes' masses, which were estimated to be over 100 times the mass of the Sun each. The study, published in The Astrophysical Journal Letters, proposes that the signal could have been amplified by a massive object located between Earth and the source, making the black holes appear more massive than they actually are. In theoretical models, black holes with masses between 60 and 130 times that of the Sun are considered rare. This "forbidden" range is thought to be problematic because massive stars typically either explode as pair-instability supernovae, leaving no compact remnant, or collapse directly into black holes without such an explosion. However, for stars with initial masses above about 140 solar masses, some models suggest they might form black holes directly without disruption. The GW231123 event, however, involves two black holes whose masses fall within the "forbidden" range, raising questions about their formation. To explain the unusual properties of the detected black holes—such as their high masses and spins—scientists have considered various possibilities. These include the formation of primordial black holes from the early universe or the repeated mergers of smaller black holes. However, models suggest that the gravitational waves from such mergers would be less likely to be detected due to the resulting black hole being propelled away from dense clusters. The new study instead explores the idea that a gravitational lensing effect could be responsible for the observed signal. Gravitational lensing occurs when a massive object, such as a galaxy or a black hole, bends and amplifies the light or gravitational waves coming from a more distant source. In the case of GW231123, the researchers developed models that combined the gravitational potential of a large-scale structure like a galaxy with that of a compact object, such as a black hole. Their analysis showed that a gravitational lens could amplify the signal of less massive black holes, making them appear as massive as the ones detected in GW231123. While the hypothesis is promising, the researchers emphasize that further observations and studies are needed to confirm it. For now, the lensing effect appears to be the most plausible explanation for the data, though the true nature of the event remains an open question in astrophysics.