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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.

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Presentation on theme: "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."— Presentation transcript:

1 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 Describe the processes involved in stellar formation 6. Stars evolve and eventually ‘die’

2 1. Formation 2. Main sequence 3. Red Giant expansion 4. Helium flash 5. Helium Depletion 6. Planetary Nebula and White Dwarfs 4. Fusion of heavier elements 5. Supernova explosion 6. Neutron stars, pulsars 6. Black Holes <5M o >5M o (too massive) Remember high mass stars burn fuel more quickly, so spend a shorter time on main sequence Outline the key stages in a star’s life in terms of the physical processes involved

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6 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 temperature of the star’s core determines which process will dominate The energy appears as K.E of the particles formed, high energy gamma rays and neutrinos (NOT correct particles here) The P-P process dominates in the Sun Describe the types of nuclear reactions involved in main sequence and post-main sequence stars

7 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 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 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 Explain how the age of a cluster can be determined from its zero- age main sequence plot for a H-R diagram

8 High turn-off point shows there are high mass stars present, so this cluster is younger and probably an open cluster Lower turn-off point from the main sequence indicates that there are not many high mass stars left so this cluster is older - likely to be a globular cluster Discuss the synthesis of elements in stars Can you discuss fusion reactions up to iron then supernova synthesis? Present information by plotting Hertzsprung-Russell diagrams for: nearby or brightest stars; stars in a young open cluster; stars in a globular cluster

9 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

10 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)

11 WHY STUDY ASTROPHYSICS?  To gain an understanding of our universe and our role in it  Learn about how the universe operates --> modern science  Observations lead to Laws such as Newtonian mechanics, which had applications for machines, construction and Industrial Revolution  Space technology gives us communication satellites, accurate weather forecasts, GPS, minerals exploration, long term monitoring of earth  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 Technology (e.g. medicine, materials, techniques) developed for space have valuable uses on earth Gather, analyse information and use available evidence to assess the impact of increased knowledge in astrophysics on society


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