Galaxy Dynamics
Date: Saturday, January 20, 2018 - 10:30
Venue: Martin Wood Lecture Theatre, Clarendon Laboratory
Who can fail to be impressed by the grand sweep of spiral arms across the face of a galaxy? Look deeper and galaxies also pose fascinating problems in non-equilibrium statistical mechanics. The dominant interparticle force (gravity) is long range, which means that galaxies have no state of maximum entropy. An important consequence is that they have long memories, which is good news for astronomers trying to understand how they form and evolve. The lectures will give a pedagogical introduction to some of the galaxy dynamics work being carried out at the Rudolf Peierls Centre.
Speakers
Stellar systems: a new state of matter
The long range of gravity means that many concepts from undergraduate statistical mechanics do not apply: energy is not extensive; there is no microcanonical or canonical ensemble. Stars and dark matter particles have long mean free paths, which means that to a very good approximation their motion is determined by the mean-field gravitational potential. James Binney will identify a hierarchy of timescales, explaining how the Boltzmann equation for the full 6N-dimensional many-particle phase space distribution function can be reduced to an evolutionary equation of a function of a mere 3 variables that is governed by the resonances among the particles' orbital frequencies.
The dynamics of galaxy discs
In galaxy discs it is energetically favourable for angular momentum to move outwards and mass to move inwards. This transportation is effected by spiral arms, but what causes them? Simple linear response calculations demonstrate that even the smallest perturbation is amplified manyfold, while the differential rotation of the disc means that the response is stretched out into a spiral-like pattern. John Magorrian will introduce the notion of the disc as a resonant cavity, within which spiral density perturbations rattle back and forth.
Dr Ralph Schoenrich
The chemical evolution side
Spiral density waves patterns re-distribute stars throughout the entire system, making it impossible to know a star's origin from just its kinematics. However, stars are more than just points in phase space: every star is labelled with the elemental abundances of the gas cloud from which it was formed. Over the last few years a number of observational campaigns have started to measure these labels for millions of stars in our own Galaxy's disc. Ralph Schoenrich will describe how chemodynamical models are being used to piece together the evolution of our Galactic environment from presolar times to the present.
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