Gravitational waves for the merger of a black hole and a neutron star have been detected for the first time

At the beginning of 2020, the Ligo, Virgo and Kagra interferometers picked up unprecedented gravitational waves: they are the first signals that prove the collision between black holes and neutron stars. And they will help us uncover other secrets of the Universe

(Artist’s impression of the merger of a black hole with a neutron star / Dietrich / Potsdam University, Max Planck Institute, N. Fischer, S. Ossokine, H. Pfeiffer / Max Planck Institute, SV Chaurasia / Stockholm University)

A long time ago, in two galaxies far distant, two neutron stars disappeared from the Universe, eat give them black holes comrades. How do we know this? Why i ruttini of those cosmic feasting they have finally come to us, after having traveled further 900 million light years, in the form of gravitational waves. Interferometers captured the signals (the first of their kind) in January 2020 Link (Usa), Virgo (Europe) e Kagra (Japan). The discovery was published recently in the magazine Astrophysical Journal Letters.

The two gravitational wave signals were picked up 10 days from each other, to be precise the January 5, 2020 (GW200105) and the January 15, 2020 (GW200115). For the scientists of the three programs, it is all about signals unpublished, the first real experimental findings that testify the fusion of black holes with neutron stars, that is, small supermassive stars. Until now, this type of merger had only been predicted by theory.

“Now we have seen the first examples of black holes merging with neutron stars, so we know they are out there”commented Maya Fishbach, a researcher at NASA and the Ligo collaboration. “Ma there are still so many things we don’t know on neutron stars and black holes: how small or large they can get, how fast they can spin, how fusion partners mate. With i future data on gravitational waves, we will have the statistics to answer these questions and, finally, learn how the most extreme objects in our universe are made “.

GW200105 it would appear loud and clear to Ligo’s detectors and it would be due to the collision between a black hole the size of 9 solar masses with a neutron star of 1.9 solar masses. The merger would take place at approx 900 million light years from Earth, but since Virgo and Kagra were unable to capture it clearly, it was not possible to precisely identify the direction of origin.

Instead, GW200115 it would be the result of the merger of a black hole with a mass 6 times that of our Sun and its neutron star by just 1.5 solar masses. The event would have happened approx 1 billion years ago. Detected by all three interferometers, the scientists were able to define the region of origin signal with greater security.

Although these are the first two signals of this type ever recorded, experts estimate that collisions between black holes and neutron stars within a billion light-years of us could occur with a frequency of 1 per month, and probably in regions of Space dense, come young star clusters o in active galactic nuclei.

“This discovery is another gem in the treasure represented by the third series of observations conducted by Ligo-Virgo. Ligo and Virgo continue to unveil catastrophic events never seen before, helping to shed light on a hitherto unexplored cosmic landscape “, he has declared Giovanni Losurdo, international coordinator of Virgo and researcher of the Infn. “We are now updating the detectors with the aim of watching even further away in the cosmos, for a deeper understanding of the universe we live in “.

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