From the collision of what is most likely a neutron star with a compact object that is 2.5 to 4.5 times the mass of our Sun.

Neutron stars and black holes are both compact objects, the dense remnants of massive stellar explosions. What makes this signal, called GW230529, intriguing is the mass of the heavier object. It falls within a possible mass-gap between the heaviest known neutron stars and the lightest black holes but the gravitational-wave signal alone cannot reveal the nature of this object, however future detections of similar events, especially those accompanied by bursts of electromagnetic radiation, could hold the key to solving this cosmic mystery.

Many OzGrav researchers across Australia, including Associate Professor Paul Lasky, were involved in this exciting discovery. OzGrav is a Centre across eight different Universities that receives funding from the Australian Research Council to perform cutting edge research in gravitational-wave discovery.

Just five days after the launch of observing run 4, things got really exciting. On May 29, 2023, that gravitational-wave signal passed by the LIGO Livingston detector. Within minutes, the data was analyzed and an alert was released publicly announcing the signal.

Astronomers receiving the alert were informed that a neutron star and a black hole most likely merged about 650 million light-years from Earth. Unfortunately, the direction to the source could not be determined because only one gravitational-wave detector was observing at the time of the signal.

The fourth observing run resumed on April 10 with the LIGO Hanford, LIGO Livingston, and Virgo detectors operating together. The run will continue until February 2025 with no further planned breaks in observing, also the sensitivity of the detectors should be slightly increased after the break.