ASTThe Formation and Dynamics of Star Clusters

One of the major questions astronomers currently face is "how do stars form?" Our own Sun is one of billions of stars that have formed in the 13-billion year lifetime of our Galaxy. When we look at these stars we see a wide range of sizes, masses and temperatures. Some stars appear isolated, others live in a binary system with another star, and some are found in groups of stars known as clusters. We think that the majority of stars form in clusters of various sizes, but recent observations have thrown doubt on this theory. By studying these groups we hope to better understand how stars and star clusters form with the wide range of properties that we see, and how this impacts the formation of planets around these stars, such as our own Earth.

So far astronomers have relied upon information from a single snapshot in time to study star clusters. This is because many astrophysical processes take millennia to occur and it is impossible to observe these processes from start to finish. While we can learn a lot about star clusters from a single snapshot (such as the number of stars in them, their total mass and age) there is a critical ingredient missing: the motions of the stars. If we can measure how the individual stars in clusters are moving, we can work out using computer simulations what the cluster might have looked like a few million years ago, and how it will continue to develop in the future. This can be important when we want to understand the structure of star clusters and whether they are expanding or collapsing.

There are two ways to measure the motions of stars in clusters. To measure the motions of stars coming towards us we use a spectrum of the light emitted by the star and measure the change in the position of spectral lines that shift according to a process known as the Doppler effect. This is the same process that changes the pitch of a siren when a fire engine travels towards you and then away from you. To measure the velocities of stars moving transversely we study images of the star separated by many years to see how the stars move relative to more stationary background stars. This is painstaking and detailed work - at the distances of these stars their transverse velocities of a few km/s are equivalent to being able to measure the rate of someone's hair growth on the International Space Station while you yourself are stood on the surface of the Earth!

My goal is use these measurements for hundreds of young stars in many different star forming regions and star clusters to understand whether these regions are expanding or collapsing and what physical mechanisms are driving these processes. This is somewhat like being at a disco, but not being able to hear the music. By watching people dance it can be possible to work out what song is playing. The same is true for star clusters: by studying the dance of the stars we can work out what physical mechanisms are at work.

What excites me about this area is the feeling that we are just now entering a new phase of exploration. Throughout the entire history of astronomy the vast majority of stars and galaxies have been static, never changing and never moving. Recent advances in detector technology and computer science combined with multi-national investment in new facilities such as the Gaia satellite and the Gaia-ESO Survey will transform our view of the sky and show us how the heavens change over time. At last we are overcoming our static view and can see the dance of the stars for the first time. For young researchers like myself, there awaits a treasure-trove of new discoveries. My project will put me at the forefront of this new era of exploitation.