Gravitational Waves
Illustration of two black holes orbiting each other, emitting gravitational waves. Gravitational
waves are a prediction of Einstein's theory of general relativity. Gravity is the distortion of
spacetime by mass, and changes in this distortion travel in waves at the speed of light. The effect
is most pronounced where extremely massive objects are subject to high acceleration. This is seen,
for instance, where black holes or neutron stars are in a close orbit such as this. In February
2016, gravitational waves were finally detected, 100 years after Einstein's prediction. The waves
emanated from the collision of two black holes, of 36 and 29 solar masses, some 1.3 billion light
years away. The waves were extremely faint by the time they arrived at Earth, where they were
detected by the two LIGO detectors in the USA.