Reports - 2012

Pictures from the Hubble Site

Astronomy Benalla  Meeting Presentations - Wednesday 17th October 2012 The Life of Stars.            Presenter: Patrick Watson The presentation started by looking at the Eagle Nebula and specifically IC 4702 and Messier 16, a star forming region some 7,000 light years away. The Pillars of Creation were shown - see below: Discussed next was a protostar, a star in the earliest phase of its life, condensing out of a cloud of gas and dust. The first stage consists of coalescing and contraction due to the mutual gravitational attraction of its parts.(Helmholtz-Kelvin Contraction).   The last phase (stellar nucleosynthesis) marks the change from the star accreting mass - into radiating energy, i.e. core hydrogen fusion (a zero-age main sequence star) The star ultimately achieves hydrostatic equilibrium and stabilises as a main-sequence or a dwarf star (hydrostatic equilibrium here refers to a balance between the inwards force of gravity and the outward pressure produced by hydrogen fusion). Further development and activity is almost totally based on the star’s beginning mass. STRUCTURE The core and envelope (radiative and convection zones) regions were reviewed, the existence and location of which are related to star mass.  ( The       symbol stands for Solar Mass eg 4       = 4 times the mass of the Sun.) EVOLUTION and END Once hydrogen burning comes to an end, stars become somewhat unstable and this is when we can find variable stars. Variability is grouped into the following types: • Eruptive • Pulsating • Rotating • Cataclysmic • Eclipsing Binary Systems - covering approx. 80 individual sub-types When core hydrogen fusion ends,  core helium fusion can begin, producing carbon and oxygen. This can be followed by carbon fusion, producing oxygen , neon, sodium and magnesium (again – depending upon beginning mass). We then followed the various trails covering development into red dwarfs, red giants, super giants, planetary nebula, white dwarfs and supernovae (with their supernova remnant) – not all of these applicable to all stars. Again, this turns out to be mainly dependent upon the star’s beginning mass.   Red Dwarf                     Planetary Nebula           Shock waves of gas sent out by the supernova are brightening the ring of debris round it There were a number of objects alluded to but not covered here:     - neutron stars, pulsars, magnetars,  and x-ray binaries / bursters / pulsars. THERE IS ALWAYS MORE