Gravitational-wave signal may have been magnified by a lens, revising black-hole mass estimate

LIGO recorded an unusual gravitational-wave event that appeared to arise from the most massive black-hole merger observed to date, with component masses of roughly 100 and 130 times that of the Sun and a combined mass estimated at about 230 solar masses. Scientists now argue that the signal may have been amplified by a gravitational lens—a massive foreground object that can bend and focus spacetime ripples much like a glass lens bends light.

Their calculations show that if a compact lens of 190-850 solar masses, or a dense structure such as a globular cluster, lay along the line of sight, the apparent masses would be overestimated, bringing the true merged mass down to around 140 solar masses. This explanation also sidesteps the need for extreme spin rates previously inferred. While the lensing of light is well documented, applying the concept to gravitational waves is still unproven, and no direct evidence of the lensing object has been found. The study calls for further observations to confirm whether such lensing can occur and what objects might serve as lenses, a finding that could reshape interpretations of distant cosmic collisions and offer new ways to probe dark matter.