The Thesis Anthology Begins – an Introduction

As promised, I am going to try and serialise my thesis in layman’s form for your “enjoyment”.  As I now officially have a PDF which contains the word “thesis” –  with text, diagrams and everything – I feel it is a good point to officially begin.  So let me introduce what on Earth it is I’m doing.My thesis will focus on protoplanetary discs.  These are frisbees of matter which form when stars are born.  The reason why they form is because of something called angular momentum.

You can see angular momentum at work when you watch an ice skater.  With their arms outstretched, the skater will rotate at a certain speed.  As the skater draws their arms towards their body, they start to rotate faster.  This is due to the conservation of angular momentum.  This is true for the skater, and for stars too.

Stars are formed from giant clouds of cold gas, mostly composed of hydrogen molecules.  These clouds are incredibly complex structures – turbulent, swirling and large enough to collapse under their own gravity.  As the clouds evolve, parts of the cloud will collapse into smaller, rotating cores.  These cores will eventually become stars.  But the core has a finite amount of angular momentum.  When the core tries to collapse under its own gravity, it needs to do something with the angular momentum it’s got.  Instead of collapsing neatly into a sphere, the core will collapse into a sort of pancake.  I’ve put an image from one of my simulations to show you what I mean.

The cloud is rotating “in and out of the page”.  Rotation supports the cloud from collapsing from the left and right, but not the top and bottom, giving the pancake you see.  The star will form in the centre of this image, and the remaining matter will form the protoplanetary disc.

Why are we interested? Because the protoplanetary disc is where planets come from (hence the name).   If we want to understand why planets are the way they are, we must understand how the protoplanetary disc makes them.  If we want to understand that, then we need to know as much as we can about the protoplanetary disc.

Next time: I’ll tell you exactly how I study protoplanetary discs.