Top 10 discoveries in astronomy

Which groundbreaking findings have contributed most to our understanding of the cosmos?

The existence of gravitational waves was first predicted in 1916 by Albert Einstein, who suggested that when two massive accelerating objects collide they cause ripples to be discharged through space, similar to the ripples seen when a pebble is thrown into water. Almost 100 years later scientists were still struggling to directly detect them, something even Einstein himself doubted could be done. When a wave passes through Earth it is squeezing and stretching the fabric of space, but as these differences are so tiny most instruments have not been able to detect these changes until recently.

Named LIGO (Laser Interferometer Gravitational-wave Observatory), this laserand mirror-based technology is sensitive to the smallest ripples through space-time. This pioneering US research facility uses two four-kilometre L-shaped detectors located in Livingston in Louisiana and Hanford in the state of Washington.

On 14 September 2015 the moment the scientists had been waiting for came when a gravitational wave rippled through the Earth caused by the violent crash of two black holes over 1 billion years ago. The first wave passed through the Livingston facility before then being deteced seven milliseconds later in Hanford, 3,000 kilometres away. Not only did this discovery prove that Einstein’s theory was right, but it will revolutionise our very understanding of the entire universe.