We have found the first ever example of a triple star system containing only pulsars and white dwarfs -the embers of ordinary stars whose time had run out. What's more, the trio dance a complex waltz that could be used to test Einstein's theory of gravity. Pulsars are ultra-dense, spinning balls of neutrons left behind when massive stars explode as supernovas. They emit radio waves from their poles that sweep the sky like a lighthouse and serve as a precise clock. When a pulsar's ticks go awry, astronomers know it has a cosmic companion pulling it to and fro.
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