Marriages Made in Heaven: the Origin of Multiple Star Systems

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Context. Most high- and intermediate-mass stars are in stable multiple systems, usually binarysystems where the two stars pursue elliptical orbits round each other, but quite often higher-ordermultiples involving three or more stars. These systems must be created as part of the star formationprocess (it is very hard to get two stars together, after they have formed). Indeed, the observationalevidence suggests that almost all stars form in multiple systems, but then some of the more fragilesystems are destroyed by external tidal forces or intrinsic instability. Forming multiple systems withthe statistical properties of observed systems is therefore one of the main challenges of star formationtheory.Project. This project will use numerical simulations to explore the formation dynamics, stabilityand orbital parameters (mass ratios, separations and eccentricities) of multiple systems, starting frominitial conditions that are informed by the latest high-resolution observations; we will be particularlyconcerned with multiple systems forming in cores that have condensed out of filaments. The majorityof stars that do not end up in multiple systems have low-mass and the project will also explorehow these objects form and why they tend to end up single. One possibility is that they form incircumstellar discs, but then fail to acquire enough mass and are ejected from the disc by interactionwith more massive siblings. An alternative possibility is that they form in the filaments that funnelmatter into forming star clusters. A third possibility is that they form in isolation, from exceptionallydense low-mass cores. We will determine which of these scenarios is most viable and why.Skills. The student will become expert in numerical hydrodynamics, magnetic, thermal, chemicaland radiative processes in star forming gas, and statistical techniques for converting observationsinto initial conditions for simulations