Cosmic gulp: Astronomers see black hole swallow neutron star

Talk about a heavy snack. For the first time, astronomers have witnessed a black hole swallowing a neutron star, the densest object in the universe — all in a split-second gulp. Ten days later, they saw the same thing on the other side of the universe. In both cases, a neutron star — a teaspoon of which would weigh a billion tons — orbits ever closer to that ultimate point of no return, a black hole, until they finally crash together, and the neutron star is gone in a gobble. Astronomers witnessed the last 500 orbits before the neutron stars were swallowed, taking less than a minute and briefly generating as much energy as all the visible light in the observable universe.

“It was just a big quick (gulp), gone,” said study co-author Patrick Brady, an astrophysicist at the University of Wisconsin Milwaukee. The black hole “gets a nice dinner of a neutron star and makes itself just a little bit more massive.” The bursts of energy from the collisions were discovered when detectors on Earth spotted the mergers’ gravitational waves, energetic cosmic ripples soaring through space and time as first theorized by Albert Einstein. They each came from more than one billion light-years away. The waves were detected in January 2020, but the study analyzing and interpreting the data by more than 100 scientists was published Tuesday in Astrophysical Journal Letters.

While astronomers had seen gravitational waves from two black holes colliding with each other and two neutron stars colliding, this was the first time they saw one of each crashing together. Neutron stars are corpses of massive stars left over after a giant star dies in a supernova explosion. Brady said they are so dense that they have about 1.5 to two times the mass of our sun but condensed to about 6 miles (10 kilometers) wide, Some black holes, known as stellar ones, are created when an even bigger star collapses into themselves, creating something with such powerful gravity that not even light can escape.

Scientists think there should be many of theses neutron star and black hole pairings, but they’ve yet to find one in our galaxy. “This is very cool,” said Johns Hopkins University astrophysicist Marc Kamionkowski, who wasn’t part of the research. He said this wwouldhelp astronomers predict how great these pairings are. Follow Seth Borenstein on Twitter at @borenbears. The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education. The AP is solely responsible for all content.