Doctorate Projects in Star Formation with Dr Andrew Walsh

Introduction

My work focusses on studying star formation throughout our Galaxy. In particular, I mainly work on how the high mass stars form in our Galaxy. Low mass star formation has been studied to a great degree over the past decades, and we understand the process in general details reasonably well. It goes something like this:

A cloud of gas and dust starts contracting under gravity (its not clear what triggers this initial collapse).
As gravity squeezes material together in the centre, it starts to heat up.
An accretion disk forms, whereby matter from the outer envelope of the cloud can be channeled through the disk and onto the warm core in the centre.
The central core warms up enough that it can sustain nuclear fusion, and a star is born.
The remainder of the accretion disk eventually become planets around the new star.

However, high mass star formation is not very well understood. This is for a number of reasons:

High mass star formation is a rare occurrence in our Galaxy - there are perhaps only a few thousand sites in a Galaxy of a couple of hundred billion stars. Because there are so few sites, they tend to be located at greater distances than low mass star formation sites. For example, there are a number of low mass star formation sites within about 100 parsecs. There are about the same number of high mass star formation sites within one kiloparsec (1000 parsecs).
When high mass stars form, they always do it in clusters along with other stars forming at the same time. This makes it difficult to disentangle the overlapping processes. It also makes it hard to find pristine environments where no previous star formation has taken place.
When a high mass star forms, the process may take only a tenth the time (or less), compared to its low mass counterparts. So it is harder to catch them in the act of forming.

So, why bother studying high mass star formation if it is so difficult? Well, high mass stars have a profound effect on their immediate environments, as well as on the much lerger scales of galaxies. They dominate the energy released in starburst galaxies. During a high mass star's life, they may release as much energy as a supernova explosion. And of course, these are the stars that will end their lives as a supernova, which enrich the Galaxy with metals (astronomerspeak for elements heavier than Helium). Their powerful, and ionising, winds create prominent bubbles called HII regions. By nature of these strong winds, and the sheer momentum dumped into their surroundings, they also have a profound effect on star formation taking place nearby.

On to a bit of history about my research.