Gwybodaeth Modiwlau

This module considers the physics of stars and galaxies and the large-scale structure of the universe. The module begins by discussing the methods used to determine the distance of stars and hence their luminosity, radii and mass. A description of the Herzspring-Russell diagram illustrates an account of the physical processes involved in stellar formation and evolution, leading to the end-states of white dwarfs, neutron stars and black holes. The physical properties, structure and morphology of the galaxies are studied. The subject of galactic dynamics is introduced.
The development of different branches of astronomy, such as radio, x-ray and y-ray astronomy, has greatly enlarged the radius of the observable Universe and uncovered many strange objects that have provided a major stimulus to the whole of physics. The kinetics of galactic rotation indicates the controlling influence of hidden mass distributed throughout a volume of space much larger than the limits of the Galaxy previously imagined. The presence of hidden mass is also indicated by the kinetics of clusters of galaxies. The accretion of mass under the pull of a strong central gravitational field, possibly centred on a black hole, is thought to provide the energy to fuel quasars and radio galaxies. These objects are so powerful they can be observed at very great distances and hence their study illuminates the nature of the early Universe. Such observations suggest a Universe that started in a "Big Bang" and has expanded to form our present Universe. This suggestion is strongly re-inforced by measurements of the microwave background radiation which originated when the Universe was only 100,000 years old. Penetrating even further back, inflation theory reconciles the isotropy of the background radiation with the limits of observation and explains why the Universe has a geometry that is almost "flat".

Introduction

Coordinate systems. Observable properties of stars. Stellar distances. Mass-luminosity relation. Introduction to the Hertzsprung-Russell diagram. Observation methods - the visible and radio "windows".
Star formation and evolution to the main sequence
Interstellar medium. Conditions for gravitational collapse of a molecular cloud. Free fall time, hydrostatic equilibrium. The virial theorem, protostar temperatures, complications beyond the simple theory. Observations of star formation, T-Tauri stars. Entry to the Main Sequence. Energy sources in stars. The nature of matter under stellar core conditions. Hydrogen Burning in MS stars. The CN cycle and p-p chain. Energy transport.
Post main sequence evolution
Post-main sequence evolution for low and high mass stars. The end states of stars: Black holes, neutron stars, white dwarfs. Supernovae, planetary nebulae.

Galactic astrophysics:

Structure of the Galaxy: core, spiral arms, halo, clusters. Galactic dynamics: the virial equation, hidden mass. Types of galaxies: spiral, elliptical, irregular. Active galaxies: Seyfert, quasars.

Relativity:

Special Theory i.e. Lorentz transformation; relativistic interval; Minkowski diagram; causality; transformation of velocities
Relativistic optics: aberration of light; Doppler effect
Relativistic Dynamics: energy momentum transformations and four vector.

Compton Scattering:

General Theory i.e. Inertial and gravitational mass; Principle of Equivalence.
Gravitational redshift; Clicks in a gravitational field. Einstein's theory of gravity; geodesics; non-Euclidean space-time. the Schwarzschild solution; black holes.

Cosmology:

Olber's paradox; the Cosmological Principle; Hubble and the expanding universe; Einstein-de Sitter model and the 'Big Bang'; steady-state and continuous creation; tests of cosmological models (number counts, microwave background); over-dense and under-dense universes; problems with expanding universe (isotropy; flatness; galaxy formation) inflation theory.