Scientists have detected the first gravitational-wave relating to a mass-gap object merging with a neutron star. This includes a mystery object that is heavier than a neutron star but lighter than black holes observed in the Milky Way. The scientists infer that the mystery object is most likely a low-mass black hole.
Gravitational waves are waves of the intensity of gravity that are generated by the accelerated masses of binary stars or where a star is close to a black hole. These function as ripples in space-time.
Prior to developing the means of measuring gravitational waves, the properties of compact objects like black holes and neutron stars were inferred from electromagnetic observations. These only provide less accurate and more indirect measurements.
In this case, the waves may signal what is happening when a black hole rips apart a neutron star.
Led by Northwestern University astrophysicists, the researchers have detected the gravitational-wave signal from a point between the merger of a potential neutron star and a mystery object in the “mass gap”. This area – the mass gap – is the term for the range that lies between the heaviest known neutron star and the lightest known black hole.
The researchers detected the signal from GW230529 in May 2023, shortly after the start of its fourth observing run. By analysing the signal, astrophysicists determined it came from the merger of two compact objects: One with a mass between 1.2 to 2.0 times the mass of our Sun and the other with a mass between 2.5 to 4.5 times the mass of our Sun.
This leads to the probability that the less massive object is a neutron star and the more massive object is a black hole.
In terms of the significance, lead researcher Sylvia Biscoveanu says: “While previous evidence for mass-gap objects has been reported both in gravitational and electromagnetic waves, this system is especially exciting because it’s the first gravitational-wave detection of a mass-gap object paired with a neutron star.”
This promises to aid future scientific inquiries: “The observation of this system has important implications for both theories of binary evolution and electromagnetic counterparts to compact-object mergers.”
The associated research paper is titled “Observation of Gravitational Waves from the Coalescence of a 2.5 – 4.5 Msun Compact Object and a Neutron Star.”
