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At the beginning of 2020, the Ligo, Virgo and Kagra interferometers captured unprecedented gravitational waves: they are the first signals that prove the collision between black holes and neutron stars. And they will help us unravel 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) Articles published today will have no title. A way to invite our readers to deepen the topics and address the issue of the polarization of the online debate. Click here to find out more .

Long ago, in two distant galaxies, two neutron stars disappeared from the Universe, eaten by their fellow black holes. How do we know this? Because the burps of those cosmic feasting have finally reached us, after having traveled over 900 million light years, in the form of gravitational waves. The signals (the first of their kind) in January 2020 were captured by the interferometers Ligo (USA), Virgo (Europe) and Kagra (Japan). The discovery was recently published in the Astrophysical Journal Letters.

The two gravitational wave signals were picked up within 10 days of each other, to be precise on January 5, 2020 (GW200105) and the January 15, 2020 (GW200115). For the scientists of the three programs, these are unprecedented signals, the first real experimental detections that testify to 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.

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

GW200105 would have appeared 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 have occurred about 900 million light years from Earth, but since Virgo and Kagra were unable to capture it clearly it was not possible to accurately identify the direction of origin.

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

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 dense regions of Space, such as young star clusters or 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, "said Giovanni Losurdo, Virgo international coordinator and Infn researcher. "We are now updating the detectors with the aim of looking even further into the cosmos, for a deeper understanding of the universe we live in."

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Physics Gravitational waves Space globalData.fldTopic = "Physics, Gravitational waves, Space"

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