On Tuesday, scientists announced that they confirmed the detection of a merger between a black hole and a neutron star for the first time. Several videos published alongside the findings illustrate what such a cataclysmic event might look like if you were able to watch it.
Neutron stars and black holes are some of the most extreme objects that we know about in the universe. The former are incredibly dense, compact objects that are left behind as remnants when massive stars explode as supernovae.
Black holes, meanwhile, are incredibly dense regions of spacetime where gravity is so strong that nothing, not even light can escape. Like neutron stars, they are also the remnants of stars that die as supernovae. However, the stars that produce black holes tend to be larger. As a result, black holes have larger masses than neutron stars.
When massive objects like black holes and neutron stars merge they produce gravitational waves, which are small ripples in the fabric of spacetime
Albert Einstein predicted the existence of gravitational waves in 1916 as part of his general theory of relativity. However, scientists were not able to directly observe them until 2015—around a century later—when LIGO (Advanced Laser Interferometer Gravitational-wave Observatory) in the United States made a historic finding, detecting the gravitational waves produced by a pair of colliding black holes.
Since then, scientists have identified more than 50 gravitational wave signals. Until now, researchers had only confidently detected waves produced by either the collision of two black holes, or the collision of two neutron stars.
But now an international collaboration of researchers has confirmed the detection of a gravitational waves produced by a third source—a black hole merging with a neutron star—according to a study published Tuesday in The Astrophysical Journal Letters.
In fact, the scientists detected two such events occurring just two days apart in January 2020 using LIGO and the Virgo observatory in Italy. The events, which both took place in galaxies at least 900 million light-years away, produced gravitational waves hundreds of millions of years ago that were detected on Earth in 2020. In both cases, the black holes likely gobbled up their neutron star companions.
"Gravitational waves have allowed us to detect collisions of pairs of black holes and pairs of neutron stars, but the mixed collision of a black hole with a neutron star has been the elusive missing piece of the family picture of compact object mergers," Chase Kimball, a graduate from Northwestern University who co-authored the study, said in a press release.
