Marriages Made in Heaven: the Origin of Multiple Star Systems

Context. Most high- and intermediate-mass stars are in stable multiple systems, usually binary systems where the two stars pursue elliptical orbits round each other, but quite often higher-order multiples involving three or more stars. These systems must be created as part of the star formation process (it is very hard to get two stars together, after they have formed). Indeed, the observational

evidence suggests that almost all stars form in multiple systems, but then some of the more fragile systems are destroyed by external tidal forces or intrinsic instability. Forming multiple systems with the statistical properties of observed systems is therefore one of the main challenges of star formation

theory. Project. This project will use numerical simulations to explore the formation dynamics, stability and orbital parameters (mass ratios, separations and eccentricities) of multiple systems, starting from initial conditions that are informed by the latest high-resolution observations; we will be particularly

concerned with multiple systems forming in cores that have condensed out of filaments. The majority of stars that do not end up in multiple systems have low-mass and the project will also explore how these objects form and why they tend to end up single. One possibility is that they form in circumstellar discs, but then fail to acquire enough mass and are ejected from the disc by interaction

with more massive siblings. An alternative possibility is that they form in the filaments that funnel matter into forming star clusters. A third possibility is that they form in isolation, from exceptionally dense 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, chemical

and radiative processes in star forming gas, and statistical techniques for converting observations into initial conditions for simulations