Sheila Rowan – TRANSCRIPT
I’d like to start with a message from the past. (Static voice recording – unintelligible) (Recording stops) That voice is a voice from history. It’s actually a voice with a song, but in truth it’s a voice with a story. What we heard is the sound of Édouard-Léon Scott de Martinville singing Au Clair De La Lune in about 1860, recorded using one of the earliest known sound recording devices, a phonautograph.
To record sound required a device that could sense vibrations – one that could take the invisible, mechanical vibrations of the air and record them using a stylus to trace them out on soot-blackened paper or glass, and preserve them, so that in future, they could be played back again and again, preserving the unique stories that those sound vibrations carry.
Last September, on 14 September 2015 in the morning, we recorded a story from the past on an astronomical scale. This time, not from 150 years or so ago, like the sound vibrations we just heard, but from 1.3 billion years ago – a story that had been traveling across the universe to us here on Earth ever since then. What we recorded was an entirely new kind of vibration. This time, not of air, but a vibration of space-time itself, a vibration of the fabric of the universe – gravitational waves.
Those first gravitational wave signals we recorded also carried a story, a story from cosmic history, a story of our violent universe. The story that they carried was one of two black holes, each tens of times the mass of our own sun sitting far out in the cosmos. Each black hole is itself the endpoint of a stellar collapse.
As a star got to the end of its life, ran out of fuel, its core collapsed under the influence of gravity and became compressed into a region of space where gravity was so strong that nothing could escape, not even light. Those two black holes were caught in a spiral, orbiting around, stretching and squashing space-time around them as they spiraled in ever closer, until eventually they merged in a catastrophic collision. The message of that collision was sent out across the universe as a pulse of gravitational waves. The energy of that pulse was equivalent to the output of all the stars in our galaxy shining for 500 years.