Ripples in time

A decade of gravitational wave detections In 2015, a new field of astronomy opened with the very first observation made beyond the electromagnetic spectrum. Elizabeth Todd looks at the milestone and what it meant

- Elizabeth Todd

Ten years ago, on 14 September 2015, a new window on the Universe was opened, giving us a novel way of studying exotic, high-energy objects such as black holes and neutron stars: the first direct detection of a gravitational wave was made by LIGO (the Laser Interferometer GravitationalWave Observatory). Now that a decade has passed, let's take a look at some of the events leading up to the groundbreaking detection of these ripples in spacetime and the exciting discoveries made since.

But where did the idea of looking for gravitational waves come from? Einstein himself suggested it, but he thought we would never detect them. This was taken as a challenge by many scientists, who set out to detect these 'undetectable' waves. In the 1960s, Joseph Weber began building resonant bar detectors, aluminium cylinders that would vibrate if a gravitational wave was to pass through. While the detectors were not shown to make detections, Weber's legacy lives on. Following his lead, having detectors at geographically separate locations helps to determine whether a signal is from a gravitational wave or a more local source such as an earthquake.

The first indirect evidence of the existence of gravitational waves was published by physicist Russell Hulse and astrophysicist Joseph Taylor Jr, who discovered the first binary pulsar system PSR B1913+16 in 1974. They knew, from Einstein's theory, that if the system was emitting gravitational waves, it would be losing energy and the stars would spiral into each other, their orbital period decreasing as the distance between them shrank. Now, with 50 years of data, the measurements agree with Einstein's predictions to within 1 per cent.

Perfecting the science