Signs of gravitational waves from black holes merged with neutron stars are recorded

The first gravitational waves have arrived, generated by the fusion of the most mysterious objects in the universe: black holes that swallow small neutron stars, i.e. what remains of collapsing stars that have become small and so dense that a spoonful of their matter weighs like a mountain . Expected for decades, there are two signals received from the European detector Virgo, in which Italy participates with the National Institute of Nuclear Physics (Infn), the American Ligo and the Japanese Kagra. Recorded in January 2020, the two signals date back 900 million years and are described in The Astrophysical Journal Letters.

A new phase of space research opens

For astrophysicists and astronomers from all over the world, the arrival of the two cosmic ‘chirps’, as the signals of gravitational waves have been called from the beginning, opens a still new phase of research: after the discovery of gravitational waves in 2016 and the arrival of multi-message astronomy, with the possibility of following cosmic events using instruments that read signals of different types, now we get to the heart and the doors are opened in search of new aspects of the universe. One hypothesis is that events such as the merger of black holes and neutron stars could occur in regions of the universe characterized by an extremely chaotic and crowded environment.

The most powerful tools for observing the universe

Now the tools that make it possible to make such complex observations are also more powerful: initially the advanced version of the Virgo detector of the European Gravitational Observatory (Ego), located in Italy, in Cascina (Pisa) and financed by Infn, worked in tandem. and the French National Research Council (CNRS), and the two American Advanced Ligo detectors (Laser Interferometer Gravitational-Wave Observatory), located in Livingston (Louisiana) and Hanford (Washington State); now from Japan Kagra (Kamioka Gravitational Wave Detector) has been added and all together work in unison as a single and gigantic antenna.

The signals detected in January 2020

The two signals are called GW200105 and GW200115, codes that identify the year, month and day of the gravitational wave (GW) observation. The first, detected on January 5, 2020, was emitted 900 million years ago when a black hole with a mass 8.9 times that of the Sun devoured, like a cosmic Pac-Man, a small star in which the sun was concentrated. mass of 1.9 times that of the Sun. The second signal, detected on January 15, 2020, dates back to about a billion years ago and was emitted when a black hole of 5.7 solar masses swallowed a neutron star from the mass 1.5 times that of the Sun. “Ligo and Virgo continue to unveil catastrophic events never seen before, helping to shed light on a hitherto unexplored cosmic landscape,” said Giovanni Losurdo, Virgo international coordinator and Infn researcher. “Now we are updating the detectors with the aim – he added – of looking even further into the cosmos, for a deeper understanding of the universe in which we live”.