Researchers from the LIGO/Virgo/KAGRA collaboration have announced the detection of an unprecedented gravitational wave signal, designated GW231123. This event marks the most massive merger of two black holes ever recorded, giving rise to a new black hole with a mass estimated to be 225 times that of our Sun. The findings were shared during the Edoardo Amaldi Conference on Gravitational Waves held in Glasgow, Scotland.
The LIGO/Virgo/KAGRA collaboration actively scours the cosmos for gravitational waves generated by mergers involving black holes and neutron stars. The LIGO observatories utilize laser interferometry techniques to detect these waves, employing powerful lasers to measure minute variations in the distance between two distant objects. LIGO operates two facilities in the United States, one in Hanford, Washington, and another in Livingston, Louisiana. Complementing these are the Advanced Virgo detector in Italy, operational since 2016, and KAGRA in Japan, which is Asia’s first gravitational-wave detector and notably constructed underground. Additionally, LIGO-India is currently under construction, with plans to be operational sometime after 2025.
Since the initial Nobel Prize-winning detection, this collaboration has recorded numerous merger events. Early findings primarily involved pairs of black holes or neutron stars. In 2021, the collaboration marked a milestone by confirming two distinct “mixed” mergers that included both black holes and neutron stars.
A tour of Virgo. Credit: EGO-Virgo
The collaboration commenced its fourth observing run in 2023, and within a year, they detected a signal suggesting a merger between two compact objects. One of these was likely a neutron star, while the other possessed an intermediate mass—heavier than a neutron star but lighter than a black hole. This detection signifies the first observation of a mass-gap object in conjunction with a neutron star, challenging the assumption that the mass gap is as unpopulated as previously believed.
