The First Neutron Star Collision We've Ever Seen



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Scientists detected something that sent the entire astronomy world into frenzy of data collection and analysis: a collision between two neutron stars — stars so dense even the space between atoms has collapsed. We knew that neutron stars could collide in theory, but this was the first time we’ve ever seen it happen. It was all made possible by the gravitational wave detector that made headlines last year by proving the existence of gravitational waves — ripples in space-time caused by some of the most extreme events in the universe. Like when two neutron stars crash into each other. But astronomers were able to study this neutron star collision using more than just gravitational waves. They also observed it with different kinds of telescopes all over the world. And this week, they released the first series of results in dozens of papers published by thousands of authors in multiple journals. So now we finally get to see what they’ve learned. Turns out, it’s a lot. Neutron stars are what’s left when a massive star, about 10-30 times the mass of our Sun, explodes in a supernova. In smaller stars, the core that’s left behind forms a white dwarf, but with stars this big, the core itself collapses. Electrons and protons combine to form neutrons, and everything gets crushed together until it’s a giant blob as dense as an atomic nucleus. A piece of neutron star the size of a sugar cube would weigh as much as Mount Everest. That’s how dense they are. Except they also tend to be about 20 kilometers in diameter. Now imagine two of these things /colliding/.I know cool guys don’t look at explosions, but even The Lonely Island guys would want to see this one. The collision was first spotted by LIGO, the gravitational wave detector, which detected100 seconds’ worth of waves. But even though it was only the fifth time we’ve ever detected gravitational waves that was almost the /boring/ part. Scientists would have expected gravitational waves from an event like this. What was exciting was that this was the first time we detected them from something other than black holes merging, something we could see with telescopes, too. By searching with those telescopes, astronomers were able to pinpoint exactly which galaxy the waves were coming from: NGC 4993, about 130 million light-years away. That meant we could get our first close-up look at the explosion of radioactive material produced by a neutron star collision, what’s known as a kilo nova. And there was a lot to see! The kilo nova put out everything from X-rays to visible light to radio waves. And, two seconds after that initial detection of gravitational waves, we also detected gamma-ray burst. Astronomers had predicted that neutron star collisions would produce tons of radiation because as neutrons were ejected in the collision, they’d form large atomic nuclei. Some of those nuclei would be radioactive and decay right away, producing radiation. And that’s exactly what we saw. We also discovered that neutron star mergers are one of, or most likely the major process that forms the heavier elements in the universe. Until now, this was entirely theoretical. We knew that elements lighter than iron could form in supernovas, but nothing heavier than that. The math said heavier elements like gold and platinum could form in a neutron star merger like this, but we could have easily been wrong. But the observations confirmed we got it right. This one collision could’ve produced up to 100 times Earth’s mass in gold. So that’s another giant mystery solved. Then there was that short gamma-ray burst: a bright flash of the highest-energy form of light. We’ve detected many of these before, but couldn’t prove what was causing them. Neutron star collisions were one of the possibilities, and this all but nails it. We saw a short gamma-ray burst from what we know was a neutron star collision. And these are just a few of the most important discoveries. This was our first chance to prove a lot of stuff that physicists had predicted for decades: gravitational waves, kilo nova’s, the creation of heavy elements, gamma ray bursts. It all checks out. With one event, we went from no direct evidence for many of these predictions, to really solid evidence. There’s an enormous amount of new research coming out of this, and a ton of things astronomers are still hoping to figure out, like what happened to the neutron stars after they collided. And this is only the beginning. As we get our new gravitational wave detectors up and running, astronomers expect to spot plenty more of these collisions, along with other types of gravitational waves, just in the next few years. We’re going to be learning a lot more about the universe pretty soon.

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