Research

Collisional evolution of gravitational N-body systems

My research focuses on the dynamical evolution of globular star clusters. The two main areas of research that I am currently working on are the phenomenon of gravothermal oscillations and the evolution of black hole sub-systems.

Gravothermal Oscillations

After an initial contraction of the core of a cluster, an isolated cluster undergoes a period of self-similar expansion. Whilst modelling this phase in the evolution of clusters, Sugimoto and Bettwieser (1983) found that if the number of stars was large enough the core radius oscillated during the expansion. This phenomenon is known as gravothermal oscillations. The conditions for the onset of gravothermal oscillations in a system containing stars of equal mass have been known for quite some time (Goodman 1987). My research investigates the conditions for the onset of gravothermal oscillations in more realistic systems (see publication list below).

Black Hole sub-systems

At the end of their life cycle, the most massive stars in a globular cluster leave behind a stellar remnant in the form of a stellar mass black hole. As the globular clusters associated with our galaxy are old objects, any stars that could have formed a black hole in a globular cluster did so long ago. If the black holes do not escape from the system during their formation, they are segregated to the centre of the system forming a black hole sub-system. Such black hole sub-systems have been suggested as a possible cause of the radius-age trend observed in the Magellanic Clouds star clusters (Merritt et al 2004, Mackey et al 2008). My research focuses on gaining a better understanding of the dynamics of black hole sub-systems particularly the lifespan of these systems.

Publication List:

P. Breen and D.C. Heggie. Gravothermal oscillations in two-component models of star clusters. Monthly Notices of the Royal Astronomical Society, Volume 420, Issue 1, pages 309–319, February 2012 Link to preprint on astro-ph

P. Breen and D.C. Heggie. Gravothermal oscillations in multi-component models of star clusters. Accepted for publication in Monthly Notices of the Royal Astronomical Society Link to preprint on astro-ph

Publications: (In review and in preparation)

P. Breen and D.C. Heggie. On the dynamical evolution of Black Hole sub-systems in star clusters. In preparation

Other interests