About 1.76 billion years ago (give or take), two circling black holes smashed into each other, birthing a new object 53 times heavier than our sun. In the process, they formed ripples in the fabric of spacetime. These gravitational waves travelled away from the site of this event, dubbed GW170814, at the speed of light, arriving at Earth on August 14. As they passed us, the two LIGO detectors and—for the first time—Italy’s Virgo observatory all caught the signal.
LIGO, or the Laser Interferometer Gravitational-Wave Observatory, is a set of two detectors located in Livingston, Louisiana and Hanford, Washington. Last year, LIGO announced it had detected gravitational waves for the first time, a major breakthrough that vindicated the predictions of Albert Einstein. In his theory of general relativity, he described spacetime as a physical substance whose shape could be altered by massive objects like black holes. When these objects undergo energetic changes—say two of them collide, a black hole consumes another massive object, or a star goes supernova—they create ripples in spacetime like the ridges you see when you toss a stone into a pond. To learn more about how black holes form, and how well the theory of general relativity holds up, we have to observe these waves—because black holes do not emit light, so we have no other way to view their behavior.
Since its initial discovery, LIGO has picked up more gravitational wave signals. And the more it sees, the less exciting each announcement might seem to the general public. Why should we care about this new one? With the new Virgo detector joining the hunt, we now have three locations scanning for gravitational waves, which will add crucial details to each sighting.
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