Stellar clusters

Stellar clusters have an impressive track-record in playing a key role in a broad range of astrophysical problems. From the structure of the Milky Way (Great Debate), stellar evolution, the stellar initial mass function to the formation of the different components of the Milky Way galaxy. 

The haloes of nearly all galaxies contain old globular clusters and they are among the first baryonic structures to form in the Universe at a redshift of z ~ 5 - 10. This makes them fascinating objects of study, because they witnessed the formation and evolution of their parent galaxy.

A huge wave of interest in star cluster research was recently sparked by the Hubble Space Telescope. Super-star clusters with masses of a million solar masses were discovered in merging and interacting galaxies, suggesting that globular cluster formation is not unique to the early Universe. Hubble also revolutionised our view on the stellar populations of old Milky Way globular clusters: the discovery of multiple main sequences and turn-offs in colour magnitude diagrams combined with several very surprising abundance anomalies have challenged popular models of star and cluster formation.

One of the science goals of our group is to understand the connection between the young massive clusters and old globular clusters to be able to use globular clusters as tracers of the formation and evolution of their host galaxy. We use observational approaches  (e.g. VLT-FLAMES Tarantula Survey) and the numerical approach by solving the N-body problem: finding the motion of N points of given masses, mutually attracting themselves as the inverse square of their distance. We do this by using fast computers with Graphical Processing Units (GPUs) to accelerate the force calculation.

Now is a particularly fascinating time to work on stellar populations and near-field cosmology: The Atacama Large Millimeter/submillimeter Array (ALMA) has recently become operational and is already putting constraints on the formation of young massive clusters and the ESA Gaia mission is due to fly in the fall of 2013. It will chart the distribution of a billion Milky Way stars in 6D phase-space. Ambitious ground based surveys have been designed to complement the Gaia astrometry and proper motions with radial velocities and chemical data (GALAHGaia-ESO, etc.) and will provide a gold mine of data on the formation of the Milky Way.

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Astrophysics Research Group
University of Surrey