Spacetime-altering shock waves came from massive neutron stars crashing into black holes millions of years ago

Black holes and neutrons stars are what is left behind when stars reach the end of their lives and collapse under their own gravity. In some cases they are born as a pair, in binary star systems where one star orbits another. Neutron stars are among the most exotic objects in the known universe. Measuring 20 miles wide they have crusts and crystalline cores. They are so dense that a teaspoon of neutron star weighs as much as Mount Everest.

“With these events [in 2016 and 2020], we’ve completed the picture of possible mergers amongst black holes and neutron stars,” said Chase Kimball, a graduate student at Northwestern University in Illinois. “That doesn’t mean that there are no new discoveries to be made with gravitational waves. There are plenty of expected gravitational wave sources out there that we’ve yet to detect, from continuous waves from rapidly rotating neutron stars to bursts from nearby supernovae, and I’m sure the universe can find ways to surprise us.”