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6. Stars evolve and eventually ‘die’ Describe the processes involved in stellar formation Space is filled with gas, dust and molecules - a sparse interstellar medium Stars form in dense clouds of this medium Gravity of denser parts of the cloud starts to attract surrounding material Increased rotation of core may lead to fragmentation that forms clusters and, later, planets Restricted movement across magnetic fields causes a disc to form Compression at the core causes temperature to rise, fusion occurs and a balance begins between thermal and gravitational pressure Outline the key stages in a star’s life in terms of the physical processes involved Remember high mass stars burn fuel more quickly, so spend a shorter time on main sequence 1. Formation 2. Main sequence 3. Red Giant expansion <5Mo >5Mo 4. Helium flash 4. Fusion of heavier elements 5. Helium Depletion 5. Supernova explosion 6. Planetary Nebula and White Dwarfs 6. Neutron stars, pulsars (too massive) 6. Black Holes Describe the types of nuclear reactions involved in main sequence and post-main sequence stars (NOT correct particles here) The PROTON-PROTON reaction and the CNO cycle both involve fusion of four Hydrogen nuclei to form a He nucleus and conversion of mass to energy The energy appears as K.E of the particles formed, high energy gamma rays and neutrinos The temperature of the star’s core determines which process will dominate The P-P process dominates in the Sun Explain how the age of a cluster can be determined from its zeroage main sequence plot for a H-R diagram Open clusters - few hundred stars, younger, high metal abundance, M to B stars, low and high mass main seq.stars, only few giant & supergiant stars Globular clusters (pictured) 100,000‘s of stars tightly bound, older, low metal abundance, mostly Hydrogen burning, M to G stars, low mass main sequence (MS) stars, many giant & supergiant high L stars There is a ‘continuum’ of H-R cluster diagrams - moving from young (with high mass MS stars) (open) to old (no high mass MS stars) (globular). MS turn-off point indicates age Discuss the synthesis Can you discuss fusion reactions up to iron of elements in stars then supernova synthesis? Explain how the age of a cluster can be determined from its zero-age main sequence plot for a H-R diagram Lower turn-off point from the main sequence indicates High turn-off point shows there are that there are not many high mass stars left so this high mass stars present, so this cluster is cluster is older - likely to be a globular cluster younger and probably an open cluster Present information by plotting Hertzsprung-Russell diagrams for: nearby or brightest stars; stars in a young open cluster; stars in a globular cluster Analyse information from a H-R diagram and use available evidence to determine the characteristics of a star and its evolutionary stage •Absolute magnitude •Luminosity •Spectral Type •Colour •Temperature •Size •Mass Present information by plotting on a H-R diagram the pathways of stars from 0.1 to 10 solar mass during their life and relate the mass of the initial protostar to the final end point Hayashi tracks (end of last chapter) Gather, analyse information and use available evidence to assess the impact of increased knowledge in astrophysics on society WHY STUDY ASTROPHYSICS? To gain an understanding of our universe and our role in it Learn about how the universe operates --> modern science Study of our solar system allows us to study data from other planets and assess the nature of our planet, its origins and our resources Space technology gives us communication satellites, accurate weather forecasts, GPS, minerals exploration, long term monitoring of earth Observations lead to Laws such as Newtonian mechanics, which had applications for machines, construction and Industrial Revolution Technology (e.g. medicine, materials, techniques) developed for space have valuable uses on earth