A collision between two neutron stars – a kilonova – has been detected for the first time. It took place 130 million years ago and produced gravitational waves, rupturing spacetime in the way predicted by Einstein.
The collision also produced gold and platinum, a process that was the accepted theory for those elements but only now can be confirmed.
The two stars collided in the Constellation Hydra in the galaxy NGC 4993, around a sextillion (a thousand billion billion) miles away from Earth. The two stars had already exploded as supernovas and had a slightly bigger mass than our sun, but were only around 30 kilometers in diameter.
The resulting gravitational waves were first detected on August 17 this year through detectors operated by the Laser Inteferometer Gravitational Wave Observatory. These detectors split a laser beam in two, sending the beams at right angles where they each hit a mirror, are reflected back and recombine.
The gravitational wave ruptured spacetime just enough that the distance to the mirrors changed, which made a detectable difference to the beams recombining. (Ironically the men behind the technology used in the detector won the Nobel Prize in Physics earlier this month.)
Less than two seconds after this happened, orbiting telescopes picked up gamma radiation from the collision, confirming that the gravitational waves did indeed result from the kilonova. Until now the only gravitational waves detected had come from black holes colliding.
The idea of a gravitational wave, which ripples through spacetime, is one of the keys two Einstein’s theory of general relativity explaining phenomena that couldn’t be explained by previous theories such as those of Isaac Newton.
Once the gravitational waves in this incident were detected, scientists were able to measure the electromagnetic radiation from the collision and how it changes in the following moments. That revealed the creation of elements such as gold and platinum. Until now, nobody had observed a collision large enough to produce the energy needed for these heavier elements.