Written by Elijah Pelofske
135 Million years ago two neutron stars collided in a distant galaxy with a very scientific sounding name – NGC 4993. In October of 2017, we detected the light and the gravitational waves that were produced when those two neutron stars collided. It took 135 million years for that signal to reach earth, specifically because the collision occurred 135 million light years away. Previously, we had only detected the gravitational waves that were produced from black hole collisions.
An excellent demonstration using a sheet and a set of heavy balls was done to show the way that gravity affects space. In the real world, we use massive detectors, one of which is called LIGO (Laser Interferometer Gravitational Wave Observatory). Teens then demonstrated the manner in which gravitational waves ripple through space—time.
The collision of these neutron stars produced something besides gravitational waves , it also produced something called a kilonova. The first thing to reach earth was the gravitational waves, and thanks to the 3 gravitational waves detectors we have positioned in throughout the world (2 in United States, 1 in Italy), the origin point of these gravitational waves was able to be localized. In all of the other previous gravitational wave detections (of black hole collisions), the localization was highly generalized – we did not know exactly where the origin point in the sky was. However, given the localization we achieved, we could point the radio and visible light observatories at that point in space and look for any electromagnetic radiation produced from the kilonova. Given that the light produced was observed here on earth, we can figure out what elements were produced in the kilonova. In this case, we found that many heavy elements were produced. Ultimately, this collision was unique in astrophysics, and answered the problem of where the majority of heavy elements (heavier than Iron) came from.
So how were these heavy elements actually produced in this kilonova? Well, the technical name is r-process, or rapid neutron capture. In a final demonstration teens joined in an activity that demonstrated conceptually how the r-process forms new elements by tossing and catching “neutrons,” to create “heavy neutron stars.” This is specifically why this discovery is so important.