4. Gravitational waves

As stars collapse they eject huge amounts of mass and energy; their gravitational field changes rapidly and, therefore, so does the curvature of the space-time around them. If the curvature of space-time is pushed out of equilibrium, by the motion of mass or energy, this disturbance travels outwards as waves. ‘Gravitational waves’ explains the effect of a gravitational wave: in a binary pulsar, the waves carry energy away from the system so that the two neutron stars slowly circle in towards each other. Gravitational waves were first detected in 2015 by the Laser Interferometer Gravitational-Wave Observatory in America. There are also plans to set up a detector in space.