1.3 billion years ago, in a galaxy far, far away two massive black holes collided in a cosmic event that made waves through the Universe and not just of the metaphorical variety. As one black hole, about 29 times the mass of our sun was pulled toward an even larger black hole 36 times the mass of the sun, the two large bodies began spiraling towards each other. The gravitational waves emitted from the black holes slowed them down and they gradually approached each other over billions of years. In the final moments of their individual existence, they speed up and collide at nearly half the speed of light, converting the mass of three suns into gravitational waves before becoming one. All of this is according to Einstein’s general theory of relativity that he proposed in 1915. He theorized that large astronomical events such as this one create gravitational waves that disturb the fabric of space and time, creating distortions that ripple outward.
Back to the present day on Earth, 1.3 billion years after the two black holes became one, the gravitational waves created by this event finally reach Earth and are detected by the twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors. One stationed in Livingston, Louisiana and the other in Hanford, Washington, both detectors are operated by Caltech and MIT. The funding for the two detectors came from numerous universities and agencies, with one of the largest investments from the National Science Foundation. It’s amazing to think that one man’s idea brought together 1,000 scientists and 90 universities and research institutions in 14 countries to prove his theory and blaze a new trail in the field of astrophysics. It is only fitting that these gravitational waves make themselves known to the human race 100 years after they were first hypothesized to exist. As the universe expands, so does our understanding of the mysteries it contains.
You may or may not be asking yourself how these scientists were able to detect such a phenomenon. Whether you want to know or not, I’m still going to give a little overview of this amazing technology. The LIGO observatory is not your normal domed-shaped structure on top of a mountain. Instead, it is a two and half mile long L-shaped interferometer. Laser light beams travel up and down the two arms, measuring the distance between the mirrors accurately placed at the end of the arms. According the Einstein’s theory, the distance measured between mirrors changes by a minute amount as gravitational waves pass through. When I say minute, I really mean infinitesimal as the change in length is smaller than one-ten-thousandth the diameter of a proton. I can fathom this infinitesimalness just as well as I can comprehend the age and vastness of the Universe.
Having two identical observatories ensures that the readings are accurate and not from a local disturbance, as well as gauges the directionality of the gravitational wave. Researchers are looking to set up another LIGO detector in India to better isolate the source location of the waves. Work is already underway to set up a space-based interferometer to detect gravitational waves off planet. You can read more about this in my Reaching Orbit article.