Julian Pittard

The rate at which massive stars blow material into interstellar space is difficult to precisely determine. Binary star systems containing two massive stars offer a means to measure this, as their winds collide at high speed with each other, producing plasma at temperatures of 10's of millions of degrees, and accelerating particles to within a fraction of the speed of light. Eta Carinae, which may be the most massive star in our Galaxy, is a member of a colliding winds system. Binary systems are also useful for understanding more complicated wind interactions, such as those that occur in super star clusters, including the central cluster of stars which orbit the supermassive black hole at the center of our Galaxy.

The winds blown by stars inflate hot, low density, bubbles in space with diameters which can exceed 200 lightyears. Recent observations have revealed that the temperature within these bubbles is unexpectedly low. A variety of processes may be responsible, and I am trying to determine which one.

Stars form in condensations (dense cores) of molecular clouds and they tend to form in clusters. Immediately after they switch on, young stellar objects inject energy in the surrounding medium through powerful jets and outflows, which are thought to be crucial for the future dynamical evolution of the parent cloud. A quantitative study of stellar feedback has not yet been done and this is still an open key question in star formation. Key questions to address include the efficiency and timescale for the winds to clear out molecular material and the evolution of the rate at which mass and energy is deposited back into the surrounding galactic medium. This is important for understanding star formation and molecular cloud evolution on a galactic scale.

When high mass stars explode as supernovae they inflate hot, low density, remnants with diameters which can exceed hundreds of lightyears. Regions of intense star formation (e.g. starburst galaxies) can later lead to spectacular bursts of supernovae - overlapping remnants may then pressurize a "superbubble" which eventually breaks out of the host galaxy as a "superwind". It is likely that the large scale structure and dynamics depends on details of the flow at much smaller scales, as described next.

The flows that occur in the above sources are not homogeneous, but rather are clumpy, dusty, and contain both thermal and non-thermal particles. The large-scale evolution and structure of such sources, not to mention the resulting emission, will depend on how these distinct components interact, and transfer mass, momentum, and energy between them. Despite this, most numerical simulations assume only a single component.

Shocks are ubiquitous in astronomy, occuring over a vast range of spatial and energy scales. It is therefore crucial to obtain a good understanding of their nature. Their study can take in a variety of interesting physics, including global oscillations and instabilities (as pictured right), particle acceleration, and the exchange of energy between different species in the downstream flow.