Astrophysicists Detect a Black Hole Gobbling Up a Neutron Star in Two Separate Events

For the first time, astrophysicists have evidence of not just one, but two black holes obliterating highly dense, incredibly massive neutron stars. First detected in January 2020, the intense gravitational waves produced by these events took roughly one billion years to reach Earth, reports Ashley Strickland for CNN.

The new study, published this week in The Astrophysical Journal Letters, is the result of collaboration among more than a thousand scientists in the field—and its findings could unlock the origins of gravitational waves and some underlying mysteries of the universe.

Both neutron stars and black holes are the results of violent star death. When stars die, depending on their size, they lose mass and become more dense until they collapse in a supernova explosion. Some turn into endless black holes that devour anything around them, while others leave behind a neutron star, which is a dense remnant of a star too small to turn into a black hole, reports CNN.

Neutron stars measure can be as small as 20 miles wide, but they are so dense that a tiny teaspoon-sized scoop would weigh as much as Mount Everest, reports the Guardian's Ian Sample. At times, neutron stars are born as a pair in binary star systems when one celestial object orbits another. Previously, binary pairs were only observed as two neutron stars or two black holes, reports Elana Spivac for Inverse.

Over a century ago, Albert Einstein first predicted the existence of gravitational waves, which are ripples in spacetime that occur when the most massive objects in the universe collide. Gravitational waves were first detected in September 2015 by the U.S. Laser Interferometer Gravitational-Wave Observatory (LIGO) when two black holes collided, reports Kenneth Chang for the New York Times.

Scientists have record neutron stars colliding with each other and black holes crashing together, but they had never collected evidence of a black hole consuming a neutron star. They suspected it was possible, but they did not have much evidence until gravitational wave detectors called interferometers provided solid evidence. Interferometers are two-mile-long, L-shaped pipes that shoot lasers. When gravitational waves pass through the detectors, they interrupt the laser's path. The dectectors are hyper-sensitive, catching interruptions a fraction of the width of a subatomic particle, reports Nell Greenfieldboyce for NPR.

The first of the collisions between the neutron stars and black holes, dubbed GW200105, was detected on January 5, 2020 by LIGO, reports the Guardian. Data collected from LIGO revealed that a neutron star twice as massive as the sun was swallowed up by a black hole nine times the size of the sun. The waves, travelling the speed of light, took 900 million years to reach Earth, reports the Guardian. The second collision named GW200115 involved a neutron star 50 percent more massive than the sun and a black hole six times more massive than the sun. GW200115 was detected by both LIGO and VIRGO, an interferometer in Italy.

Researchers suspect violent neutron star-black hole collisions occur at least once a month within a billion-lightyear radius of Earth, reports CNN. With upgrades to LIGO and VIRGO, more of these collisions are likely to be detected. Researchers hope to witness a neutron star get shredded into fragments of light as a black hole devours it, NPR reports. For these recently detected collisions, no light was emitted because of the distance and how massive the black holes were compared to the smaller neutron stars, reports CNN.

"These collisions have shaken the Universe to its core, and we've detected the ripples they have sent hurtling through the cosmos," study coauthor Susan Scott, a theoretical physicist at Australian National University, says in a statement. "Each collision isn't just the coming together of two massive and dense objects. It's really like Pac-Man, with a black hole swallowing its companion neutron star whole. These are remarkable events and we have waited a very long time to witness them. So it's incredible to finally capture them."

Elizabeth Gamillo | | READ MORE

Elizabeth Gamillo is a correspondent for Smithsonian and a science journalist based in Milwaukee, Wisconsin. She has written for Science magazine as their 2018 AAAS Diverse Voices in Science Journalism Intern.