In June 2021, a detection of a collision between a neutron star and a black hole was confirmed by researchers for the first time. They detected two events occurring 10 days apart in January 2020 that made splashes which sent gravitational waves in space that rippled across 900 million light-years to reach Earth in which case the neutron star was likely swallowed whole by its black hole partner.
Recently, an observation of colossal new events that release gravitational waves was announced by the international collaboration of LIGO-Virgo-KAGRA. There were tiny vibrations in the fabric of space-time. The cosmic collision causes these gravitational wave events. Thirty-two of them involve two black holes smashing each other. There are two more events involving black hole and neutron star collisions. The final one is still uncertain as to what type of compact exact object was involved.
The 35 new events cover the entire mass range of gravitational waves that have been detected which means black holes of all shapes and sizes have been observed colliding.
On the 5th of January 2020, the first merger was detected that involved a black hole about 9 times the mass of our sun and on January 15 of the same year, the second merger was detected that involves a 6-solar-mass black hole and a 1.5 solar-mass neutron star. Astronomers spent decades searching for neutron stars that might be orbiting black holes in our home galaxy, the Milky Way but have found none. Even though they see a strong signal in one detector, they conclude that it is real and not a detector noise. It passes their stringent quality checks and sticks out from all noise events they see in the third observing run. Since the signal was strong in only one detector, its location of the merger on the sky is still uncertain and lies somewhere in an area about 34,000 times the size of a full moon.
The second half of the third observing run for the LIGO and Virgo gravitational wave observatories were switched on, studying the universe between November 2019 and March 2020. The data has been submitted for publication together with three companion papers that bring the total number of gravitational wave detections to 90.
“Only now are we starting to appreciate the wonderful diversity of black holes and neutron stars,” said Christopher Berry, a key member of the Laser Interferometer Gravitational-Wave Observatory (LIGO) Scientific Collaboration (LSC). “Our latest results prove that they come in many sizes and combinations. We have solved some long-standing mysteries but uncovered some new puzzles too. Using these observations, we are closer to unlocking the mysteries of how stars — the building blocks of our universe — evolve.” -NORTHWESTERN NOW
An uncertain merger event is believed to be between a black hole 24 times the mass of our sun and a much lighter black hole. A very heavy neutron star couldn’t be excluded while the researchers believe that a light black hole fits the profile better which is similar to a previous puzzling event recorded by the collaboration.
According to Hannah Middleton, a postdoctoral researcher at OzGrav, University of Melbourne, “Each new observing run brings new discoveries and surprises. The third observing run saw gravitational wave detection becoming an everyday thing, but I still think each detection is exciting!"
The two observatories, LIGO which is located in the US, and Virgo, located in Italy are currently off and doing some upgrades in preparation for their fourth observing run. They will be joined by the KAGRA observatory in Japan and will be online in late 2022.
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