Potential Stars and Planets PhD Projects

Project: Secular Dynamics and Chaos in Multi-Planet Systems

Supervisor: Dr. Will Farr

Secular Dynamics and Chaos in Multi-Planet Systems

Based on data from the Kepler mission, we now think that planet formation is "fertile" (that is, multi-planet systems are more likely than would be expected from a Poisson distribution). In systems with multiple planets, the planets can influence each other gravitationally; we believe that many of the systems we observe bear the imprint of gravitational interactions between their constituent planets.

This project would use an in-house code that is capable of rapidly simulating the secular (long-timescale) gravitational interactions between planets to explore the effects of these interactions. Possible areas of investigation include:

The effects of (unobserved) distant planets on inner planets, possibly including coherent Kozai oscillations of the inner planets and subsequent tidal circularization producing systems like the five-planet Kepler 20.

Statistical studies of the effects of secular interactions and particularly chaos on the observed population of extra solar planets. This project would involve both dynamical calculations and also statistical analysis of existing exoplanet data.

Generalization of the existing code to incorporate brief periods of short-timescale interactions between the planets by transiting to traditional N-body integrators for these times and reverting to the secular approximation when possible. Such a code would have the short runtime of the secular code, but include all gravitational effects when necessary.

For more information please contact Dr. Will Farr (Email: wfarr[at]star.sr.bham.ac.uk)

Project: Massive Stars and Star Clusters

Supervisor: Dr. Ian Stevens

Massive stars (OB and Wolf-Rayet stars) have enormously strong winds, with terminal velocities of 3000 km/s and mass-loss rates that are vastly stronger than that of the solar wind. These winds shape the environments of the stars and the star clusters they are in. The mass-loss process dominates the stellar evolution of massive stars, determining the final outcome - a black-hole or neutron star. These massive stars are the the most likely progenitors of the recently discovered gravitational wave sources. Radio emission is one of the main ways of studying the mass-loss from these massive stars, which emit free-free emission, as well as synchrotron emission from shocks embedded in the winds.

More recently, many massive stars have strong surface magnetic fields (several kilo-Gauss), and these magnetic fields affect the dynamics of the stellar winds. These strong fields will shape the winds in the inner "magnetosphere" of the O-star. This will impact the radio emission, with a non-spherical wind giving rise to variable radio emission.

Excitingly, several new major radio telescopes are available now (ASKAP, MEERKAT, JVLA, e-Merlin), all leading up to the Square Kilometre Array (SKA), which will revolutionise our view of the radio sky. We expect a range of important new observations on massive stars.

i) New radio observations of magnetic massive stars: Using the new generation of radio telescopes to produce lightcurves of unprecedented sensitivity, covering at least one rotation period of the star, to look for variability in O-stars. Part of the project will be identifying the most likely candidates for seeing magnetic effects. The structure of these lightcurves will yield insights into the structure of the wind - constraining the mass-loss process, and emission mechanisms.

ii) Colliding Winds: We can also observe (and model) massive binary systems, where both components have winds and this results in an energetic wind collision region, and showing thermal and non-thermal radio emission. Detailed multiwavelength studies of such objects, such as Eta Carina and WR147 are underway.

iii) Next-generation Radio Surveys: The student will be involved in one or more radio surveys of regions in our Galaxy containing massive stars, taken with e-Merlin, JVLA or MeerKAT. These surveys are precursor of large surveys to be done with the SKA.

For more information please contact Dr. Ian Stevens (Email: irs[at]star.sr.bham.ac.uk)

Project: Evolution of massive stellar binaries

Supervisor: Prof. Ilya Mandel

Recent observations suggest that the vast majority of massive stars in the Universe are born in binaries, and some may even be born in triples. Morevoer, most of these stars will interact during their lives, transferring mass to each other as they evolve, and possibly entering a common envelope if mass transfer during Roche lobe overflow becomes unstable. Sufficiently massive stars will eventually undergo core-collapse supernova and form neutron stars or black holes. The study of these systems is critical to understanding a variety of short-lived and long-lived astrophysical transients: X-ray binaries, type Ib/c supernovae, long and short gamma ray bursts and their afterglows, kilonovae, and gravitational waves. As part of this project, you will develop our group's work on understanding the evolution of such systems, particularly by making comparisons with observations in order to constrain the physics governing massive binary evolution.

For more information please contact Dr. Ilya Mandel (Email: imandel[at]star.sr.bham.ac.uk)