For the first time, the phenomenon of the merger between a black hole and a neutron star has been clearly detected using gravitational waves.
Gravitational waves are tiny ripples in spacetime and were first observed in 2015, a century after Albert Einstein predicted their existence in his General Theory of Relativity.
A black hole is basically the corpse of a star pressed in on itself by its own gravity, lacking the force that kept it “swollen.” Once that colossal state of compression is reached, its gravitational field becomes so powerful that it absorbs everything that passes nearby, including light itself. That is why it does not emit or reflect any light. The same explanation can be applied to a neutron star, with the exception that its mass is less and does not reach as much density as a black hole, so light does escape from the neutron star.
Scientific teams from LIGO, Virgo and KAGRA, three gravitational wave detection facilities, have announced the first detections of gravitational waves resulting from the merger between black hole and neutron star. Virgo’s science team includes specialists from the National Center for Scientific Research (CNRS) in France.
Although only a few years have passed since the first detection of gravitational waves, the technique has made it possible to capture a wide repertoire of phenomena related to massive cosmic objects. The LIGO and Virgo detectors have already observed mergers between the members of pairs of black holes and, less frequently, of neutron stars in pairs of this type. However, two gravitational wave detections in January 2020, after careful scrutiny, now provide evidence of mergers of a different kind. The bursts of gravitational waves, one called GW200105 and the other called GW200115, due to their detection dates, were produced by a process that had already been predicted but had never been observed before: the fusion between members of a mixed pair composed of a black hole and a neutron star. Such a merger results in a black hole.
An artist’s recreation of a black hole and a neutron star spinning closer and closer to each other, shortly before their collision and merger. (Image: © Carl Knox, OzGrav – Swinburne University)
Gravitational waves contain valuable information about their source, such as the mass of the components that make up the pair or binary system. Analysis of the signals revealed that GW200105 was the result of the merger, some 900 million light-years away from Earth, of a black hole and a neutron star, respectively 8.9 times and 1.9 times more. massive than the Sun. As for GW200115, it originated in a merger, which occurred about a billion light-years away, between a black hole and a neutron star with masses 5.7 and 1.5 times greater than the from the Sun, respectively. (Source: NCYT from Amazings)