New Delhi: The LIGO, Virgo and KAGRA observatories forming the LVK Collaboration have released the Gravitational Wave Transient Catalogue 4.0 (GWTC 4.0),
adding 128 new gravitational-wave candidates from the first part of their fourth observation run, which ran from May 2023 to January 2024. This more than doubles the previous total of 90 candidates from the first three observing runs, combined. There have been over 300 mergers detected in the fourth run so far, with more expected to be added in future catalogue updates. The expanded catalogue was enabled by improvements in detector sensitivity and analysis techniques between runs.
Gravitational waves originated from interactions between dense objects such as black holes and neutron stars. Most detections involve binary black hole pairs of similar masses, typically containing tens of solar masses, spiralling together and merging into a single, more massive black hole. The new catalogue shows a greater variety of events, including the heaviest black hole binary detected to date, with each black hole containing around 130 solar masses, indicating that they formed from prior mergers between lower-mass black holes. Another detection features exceptionally high spins, with both the black holes in the binary pair rotating at about 40 per cent the speed of light. This system also indicates that previous interactions increased the spin of both the black holes. One merger had a black hole twice as massive as the other.
Tracing the life cycles of stars
The catalogue also includes two mergers between black holes and neutron stars. These observations expand the knowledge of black hole formation from the collapse of massive stars, and reveal differences in spins between early and late-universe mergers, with the early black holes tending to spin faster. The detections provide insights into astrophysical processes as well. The detections also rigorously test general relativity in extreme conditions. The catalogue is also contributing to measure the Hubble constant, or the rate at which the universe is expanding. The findings reveal that gravitational wave astronomy has come a long way since the first detection in 2015.
