In case you haven’t heard about LIGO or Laser Interferometer Gravitational Waves Observatory, you’ve been missing out on a lot. LIGO is a gravitational wave observatory. LIGO is blind to visible light and the rest of the electromagnetic spectrum, all it cares about is detecting gravitational waves, which, unlike physical light, is not a part of the electromagnetic spectrum. The LIGO s made up of twin sites in Louisiana and Washington. The LIGO made the headlines when it observed two neutron stars combining, the first and only one of its kind yet recorded. This astronomical revolution comes less than two years after the first gravitational wave was detected. Astronomers have been trying to figure out how to detect these ripples for the last century, ever since they were first predicted by Albert Einstein in his theory of general relativity. Einstein argued that objects in the Universe actually warp the space and time around them.
And when they move, they create waves in this space-time, a bit like a boat leaving ripples in a pond. But detecting these waves is an incredibly difficult process. The ripples from nearby planets and stars, for instance, are much too small to pick up. That’s why scientists look for the biggest waves they can find – ones coming from the most massive objects in the Universe moving at rapid speeds. Merging black holes and neutron stars offered the perfect targets. Until now, though, all four of the detections made by LIGO have been from mergers of black holes.
These discoveries told scientists a great deal about the types of black holes found in our Universe, but they don’t offer much opportunity for follow-up observations. Black holes have incredibly strong gravitational pulls, so nothing, not even light can escape from them. Even if astronomers could pinpoint where a black hole merger occurred, telescopes that observe light wouldn’t be able to see anything.
That’s why astronomers have been eager to find merging neutron stars and finally they got the chance they had been eagerly waiting for, just after the establishment of the new gravitational waves observatory, Virgo in Italy. Having three detectors pick up waves makes it much easier to find the sources of these signals in the sky. By timing when the waves reach each detector, astronomers can triangulate the location of the wave source in space. As soon as the LIGO team suspected they had caught a new wave, text alerts were sent to astronomers around the world, telling them to get ready for a hunt. Based on the LIGO measurements, the two neutron stars combined 130 million light-years away, much closer than the black hole mergers which occurred billions of light-years beyond Earth. And each neutron star was between 1.
1 and 1.6 times the mass of our Sun, though they were probably just about 10 miles across. Their resulting impact is known as a kilonova, an incredibly explosive event. The merger creates a gargantuan fireball, and the superdense materials from the two stars shoot outward in all directions. Initial light measurements from the kilonova show just how fast that material was moving, too: the outer layers of the kilonova sped away from the event at speeds close to one-third the speed of light, according to astronomers’ estimates. These events aren’t just explosive either; they’re also thought to be factories for the production of the heaviest elements in the Universe. And the light emitted from the kilonova showed how those elements, such as gold, were produced in the wake of the merger.
Being called as one of the greatest discoveries of the decade, this event surely marks the beginning of a new era of universal understanding.