Gamma-ray bursts from ultra-compact binary stars

I am studying how gamma-ray bursts are made from massive, interacting stellar binaries. Gamma-ray bursts are extremely high-energy flashes of gamma-rays from deep space. They have inspired much recent activity with two dedicated space telescopes. The longer bursts are believed to form in the collapse of rapidly-spinning massive stellar cores. By computing the evolution of massive binary stars I will attack the key problem: how to keep the star spinning sufficiently rapidly right up to the point when it collapses. Shorter bursts probably form in the merger of two compact stellar remnants: neutron stars or black holes. Such binaries are also interesting as sources of gravitational waves. I will study the formation of these ultra-compact binaries in the field, incorporating knowledge from observations of Galactic binaries to predict their formation rates and properties. We have shown that some short gamma-ray bursts are found at very large distances from the centres of their host galaxies. I will model the formation of compact binaries in the cores of rich stellar clusters, which is a likely explanation of these distant bursts. In high-density environments stars come close enough to interact and even collide. This drives up the number of compact binaries expected in dense stellar clusters. Recent observational results predict that stellar clusters were much more massive at early times, increasing their importance as sources of compact binaries.