How do gravitational waves travel across the universe?

Gravitational waves are disturbances in spacetime predicted by Einstein in 1916 and first directly detected by LIGO in 2015. They are produced when very massive objects, such as black holes or neutron stars, orbit each other and accelerate asymmetrically. As the waves pass, they slightly stretch and squeeze distances in perpendicular directions. LIGO’s first detection came from a black-hole merger about 1.3 billion light-years away, showing that these waves can cross enormous cosmic distances with little loss. Gravitational-wave astronomy has opened a new way to study the dark, violent universe.