Kilonova: Colliding Neutron Stars

A little update on where I am with everything at the moment. Again I am incredibly apologetic for updating less frequently recently due to a lot going on. As you might already know, I entered the Breakthrough Junior Challenge, been notified as a semifinalist, and recently crowned Regional Champion of Europe – the popular vote process definitely was more time consuming than I had imagined, but now (I hope) I can share with you some of the exciting things I’ve been wanting to write about for a while.

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Firstly this post is on what I consider as THE BIGGEST DISCOVERY IN PHYSICS this year – the neutron star collision. You might already know that the 2017 Nobel Prize in Physics was awarded to the three leading physicists who were involved in a worldwide collaboration in the search for gravitational waves. The “kilonova” on August 17th was not only a detection of another gravity wave but it also unveiled so many more utterly amazing things about the cosmos we were yet to discover.

Neutron Stars

To start off let’s jump straight into the science behind the event of colliding Neutron stars. Neutron stars can be thought of as the less extreme versions of black holes – which are a result of very massive stars collapsing under their own gravitational pull and forming a point of infinite space-time curvature. These stars are the remnants of the supernovae of stars that are roughly 10 to 29 solar masses, too big to form a white dwarf (like how our own Sun will after its death) and too small to form a black hole. When a star this size explodes, its gravity is so strong that it literally forces electrons and protons to combine into neutrons, and the neutron star is stopped from further collapse by neutron degeneracy pressure. Neutron stars are extremely small and dense, their diameters are the size of cities but a teaspoon can be the weight of Mount Everest. Thus, there is no wonder how they produce immensely strong gravitational fields and not only cause gravitational lensing but also gravitational waves.

Gravitational Waves

We have detected gravitational waves using LIGO (Laser Interferometer Gravitational-Wave Observatory) several times before the one from the kilonova, the first announced early 2016 when they were spotted from merging black holes a billion light-years away. Einstein predicted exactly a hundred years ago in his theory of General Relativity (which is one of the two huge pillars of modern physics almost perfectly describing everything from a macroscopic to a cosmic scale) that Space and time are woven into one “fabric” of space-time. A steel ball would bend a rubber sheet more than a table tennis ball would, same goes with space, the more massive the object the more it would distort space-time. When very heavy masses (this must be the case due to Gravity being the weakest force by far) accelerate around each other, they will cause changes in the distortion. This means that violent cosmic events should send ripples travelling at the speed of light outwards through this fabric causing space to stretch in one direction and compress in the other direction: Gravitational waves!

The reason why Physicists have been so hyped about this discovery is that the effects of gravitational waves are absolutely minuscule so we needed extremely sensitive equipment that would not be affected by surrounding movement. The precision required for this experiment to work is far more than we can imagine. What physicists were trying to do is a bit like measuring a length difference of 5 millimetres in a stick that is one unvigintillion metres (1×10^21m or around the diameter of our entire galaxy). Just pause at that for a minute.

So you might ask, gravitational waves have been detected 4 times already, what’s so exciting about this fifth discovery?

For starters, all of the gravitational waves detected before came from merging black holes and scientists have been confident that colliding neutron stars also cause the ripple effect in space-time but were yet to detect it directly. This time, however, what really was astonishing was seeing gamma-ray bursts right after the waves.

Gamma-ray bursts are the most energetic and brightest cosmic events that blast radiation across many light years of distance. With this discovery, we were able to detect both the gravity and light show that the neutron stars gave out during their merge!

This was further evidence to show the origins of elements after iron in the periodic table as it was long believed that only kilonovae had enough energy to create heavy elements such as gold and platinum. By studying the observations of telescopes such as Hubble, exact elements produced from the collision were traced.

Crazy or what?

Author – Susan Chen

Susan is a 6th year high school student currently studying three STEM subjects at Scottish Advanced Higher level – Mathematics, Physics and Chemistry. She particularly loves ideas in cosmology and hopes to embark on an academic journey in the area of Physics.