Astrophysics Formal Seminars

Formal seminars take place every Monday during full term. For a complete list of talks please visited the talk.cam website.

Title to be confirmed

Abstract not available

Quasi-periodic oscillations and the global modes of magnetohydrodynamic, relativistic accretion disks

The high-frequency quasi-periodic oscillations (HFQPOs) that punctuate the light curves of X-ray binary systems present a window onto the intrinsic properties of stellar-mass black holes and hence a testbed for general relativity. One explanation for these features is that relativistic distortion of the accretion disc’s differential rotation creates a trapping region in which inertial waves (r-modes) might grow to observable amplitudes. In this talk, I will address previous local analyses predicting that this trapping region may be destroyed by large scale magnetic fields, presenting global calculations of r-modes in a magnetohydrodynamic model of a relativistic accretion flow.

Title to be confirmed

Abstract not available

Revisiting relaxation in globular clusters

The classical (Spitzer-Chandrasekhar) theory of cluster relaxation is unsatisfactory because it involves the Coulomb logarithm and completely neglects the cluster’s self-gravity. A modern alternative is the Balescu-Lenard (BL) equation, which has no such ill-defined parameter and includes self-gravity. The BL equation has recently explained the secular evolution of collisionless stellar discs. In this talk I will review the classical theory and demonstrate its pitfalls, showing at each stage why the BL equation does a better job. I will then present the first application of the BL formalism to spherical systems. I will show how the BL flux through action space differs from the corresponding classical flux, and discuss what a complete theory of cluster relaxation might entail.

Based on Hamilton et al. (2018) https://arxiv.org/abs/1803.11091.

Title to be confirmed

Abstract not available