Last summer, astronomers around the globe turned their telescopes to a single spot in the sky. What they all observed that day and for the next few weeks was a rare kilonova, a collision much more violent than a supernova, occurring in the NGC 4993 galaxy, 130 million light years away (in kilometres: imagine 123 with twenty-one zeros after it). This gigantic explosion was the result of the collision of two neutron stars, namely two extremely dense stars (dense enough to have a teaspoon of its matter weigh a billion tons!). The collision was due to the force of their mutual gravitational pull. These two stars had begun to spin around each other at significant fractions of light speed, getting closer and closer together until they collided. It was this collision that was observed on August 17th.
The first to detect the kilonova was the Fermi Gamma-ray Space Telescope from NASA. The telescope, as its name implies, detected the jet of deadly and extremely powerful gamma rays being ejected from the collision. Seconds afterwards, the North American LIGO Laboratory and the European VIGO Laboratory detected the gravitational wave emanating from the kilonova. Most importantly, telescopes on Earth and in orbit could visually observe the event, a first for astronomy. Indeed, neutron star collisions had been known to happen in the past, but for various reasons, they could not get images of it. Now, telescopes like the Hubble Space Telescope can obtain beautiful images of the event.
However, this collision was not important solely because we could take cool pictures of it. It provided good insight into questions astronomers had been debating for years.
According to Einstein’s theory of general relativity, spacetime is like a bendable fabric. Spacetime can be thought of as a trampoline. If you place a heavy object on it, it will stretch and curve. It is the same with planets, stars and galaxies in space. When extremely massive objects move through space or collide with each other, Einstein’s theory predicts that the event will cause a gravitational wave to spread across space. Think of this as a pebble thrown in a still pond: the pebble will cause ripples to spread across the water. What LIGO Laboratory detected in August was a single gravitational wave that made its way to Earth, only detectable with the laboratory’s extremely sensitive tools. The result: a great boost in proving Einstein’s widely accepted theory of general relativity.
Origin of Gamma Ray Bursts
Thanks to Fermi’s observation of the gamma ray burst that came out of the cataclysm, scientists now have a better picture of the origin of these deadly rays. Gamma rays are high energy electromagnetic waves. Scientists had theorized for years on their origin, and the burst detected by Fermi consolidated their belief of gamma ray bursts originating from high energy collisions.
A Cosmic Gold Mine
The kilonova in the Hydra constellation also provided scientists with one last piece of information. Have you ever wondered where the gold in your grandmother’s ring came from? Sure, it was mined from the earth, but how did it get there in the first place? After analysing the remnants of the neutron star collision, astronomers could determine the nature of the residue. It turns out that what was left of the explosion was a wealth of heavy metals such as gold, platinum and uranium. The amount of these metals ejected from the star that are now floating away in space is equivalent to 1300 times the mass of the Earth! Now astronomers can theorize with more certainty that the gold in our jewelry draws its origin from the vast universe.
The recent collision of two neutron stars provided a wealth of information (not just of gold) for astronomers around the globe. With these new findings, scientists are becoming more confident about what they theorize. More events like these are sure to have a great impact on our future scientific knowledge.
Virginia Rufina Marquez-Pacheco
Science & Tech Editor
Originally published in Bandersnatch Vol. 47 Issue 05 on November 8, 2017