External Seminars

The following talks take place at DAMTP, the Cavendish Laboratory or the Institute of Astronomy and are not organised by this group. However, they might by related to research that is done within this group at DAMTP.

The Gaia Sausage - our Galaxy?s last major merger

Abstract not available

Part of Institute of Astronomy Seminars
Speaker: Vasily Belokurov
Wednesday 20 February 2019, 13:15-13:45
Sackler Lecture Theatre, IoA.

Sausage-Mania ? more Mouth-watering Recipes

Abstract not available

Part of Institute of Astronomy Seminars
Speaker: Wyn Evans
Wednesday 20 February 2019, 13:45-14:15
Sackler Lecture Theatre, IoA.

The computational challenge of the Square Kilometre Array

The Square Kilometre Array (SKA) which is due to become operational in the mid-2020s will be a step change in Radio Astronomy. The deluge of data that the SKA will produce will be challenging to process. I will talk about the science goals of the SKA and the design of the high-performance computing systems to process the data.

Part of Data Intensive Science Seminar Series
Speaker: Mark Ashdown - SKA
Thursday 21 February 2019, 13:00-14:30
Kavli Large Meeting Room, Kavli Building.

Transformative advances in post-main-sequence planetary system science

Connecting planetary systems at different stages of stellar evolution helps us understand their formation, evolution, and fate, and provides us with exclusive and crucial insights about their dynamics and chemistry. Post-main-sequence white dwarf and giant branch stars host planetary systems that include a variety of observed objects and phenomena, such as planetary debris discs, disintegrating and embedded asteroids, and photospheric metal pollution. Here, I provide a review of both our current knowledge of these systems and models which have been used to explain them. I also highlight the transformative advances expected in upcoming years with the current and next generation of ground-based and space-based initiatives. Looming orders-of-magnitude increases in available data must be accompanied by novel theories and simulations in order to understand the results from this interdisciplinary and expanding research field.

Part of Institute of Astronomy Colloquia
Speaker: Dimitri Veras (Warwick)
Thursday 21 February 2019, 16:00-17:00
Sackler Lecture Theatre, IoA (tea at 3:30 pm).

The discreteness-driven relaxation of collisionless gravitating systems

The violent relaxation of a perturbed or collapsing collisionless gravitational system, with the fast achievement of a quasi-stationary state, is traditionally assumed to be governed by the Vlasov equation, in which case the entropy must be conserved. In this scenario, the reconciliation with the 2nd law of thermodynamics is made through coarse-graining (a subjective effect). In this talk, I will discuss recent results obtained with entropy estimates in N-body simulations and for orbit ensembles in fixed external potentials. In the N-body simulations, the (slow) long-term evolution is well described as resulting from two-body relaxation, while the early evolution generates a fast (in a few crossing times) entropy production. The integration of orbit ensembles in external potentials shows that this early collisionless relaxation is due to the discreteness (finite N) of gravitating systems in any potential, being a consequence of the Nyquist-Shannon theorem, which precludes the development of phase-space structures finer than a typical scale _{N^{-1/d (for a sample of size N in d dimensions). As a result, a typical relaxation time T/tau_cr}} 0.1 * N1/6 emerges in integrable potentials, with weaker N-dependencies in the presence of chaotic orbits. Furthermore, this scenario avoids the need for the subjective effect of coarse-graining and indicates that the Vlasov equation does not provide an adequate kinetic description of this fast (violent) collisionless relaxation.