This post is part of a series about quick questions and answers about the Virgo experiment and the science of gravitational waves. Do you have a quick question yourself? Tell us and we will reply!
“What are gravitational waves?”
Gravitational waves are ripples in spacetime that propagate throughout the Universe at the speed of light. These waves are produced by the most violent astrophysical phenomena, such as the merger of neutron stars and/or black holes, as well as the explosion of massive stars as supernovae. Gravitational waves are one of the predictions of the theory of general relativity published by Albert Einstein about a century ago, at the end of 1915. However, it is only in the last few decades that have we had developed the technology required to build sensitive enough instruments like Virgo, which are designed for the direct detection of gravitational waves on Earth.
For decades, there was only some indirect evidence for the existence of gravitational waves. The most significant was based on PSR B1913+16, a pulsar in orbit around another compact star. Measuring the pulsar timing behavior of PSR B1913+16 over three decades, it was shown that the evolution of the orbital period was consistent with a loss of energy due to emission of gravitational waves. The first direct evidence for gravitational waves came in September 14, 2015, when the two LIGO detectors recorded a gravitational wave signal emitted from two merging black hole. The event, called GW150914, marked the beginning of the era of gravitational wave astronomy.