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6. Stars evolve and eventually ‘die’

ASTROPHYSICS. Caroline Chisholm College Physics. Describe the processes involved in stellar formation. THE FORMATION OF STARS. Space is filled with gas, dust and molecules - a sparse interstellar medium. 6. Stars evolve and eventually ‘die’. Stars form in dense clouds of this medium.

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6. Stars evolve and eventually ‘die’

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  1. ASTROPHYSICS Caroline Chisholm College Physics Describe the processes involved in stellar formation THE FORMATION OF STARS Space is filled with gas, dust and molecules - a sparse interstellar medium 6. Stars evolve and eventually ‘die’ 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 A STAR IS BORN

  2. ASTROPHYSICS Outline the key stages in astar’s life in terms of thephysical processes involved Caroline Chisholm College Physics See the separate powerpoint presentation (modified from an original NASA presentation) on the 'Life Cycles of Stars' for more info 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 5. Helium Depletion 6. Planetary Nebula and White Dwarfs 4. Fusion of heavier elements 5. Supernova explosion (too massive) 6. Neutron stars, pulsars 6. Black Holes

  3. Caroline Chisholm College Physics

  4. ASTROPHYSICS Caroline Chisholm College Physics Supernova remnant = Dust/gas Cloud (nebula)

  5. ASTROPHYSICS Caroline Chisholm College Physics Dust/gas Cloud (nebula) Main sequence star Supernova

  6. ASTROPHYSICS 2 E = mc Describe the types of nuclear reactions involved in main sequence and post-main sequence stars Caroline Chisholm College Physics (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

  7. ASTROPHYSICS Explain how the age of a cluster can be determined from its zero-age main sequence plot for a H-R diagram Caroline Chisholm College Physics 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 CLUES TO STAR FORMATION AND AGES OF 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

  8. ASTROPHYSICS Can you discuss fusion reactions up to iron then supernova synthesis? Caroline Chisholm College Physics Explain how the age of a clustercan be determined from itszero-age main sequence plotfor a H-R diagram Discuss the synthesisof elements in stars turn-off point 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 High turn-off point shows there are high mass stars present, so this cluster is 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 practical exercises 5.2, 5.3

  9. ASTROPHYSICS Caroline Chisholm College Physics Analyse information froma H-R diagram and use availableevidence to determine thecharacteristics of a star and itsevolutionary stage • Absolute magnitude • Luminosity • Spectral Type • Colour • Temperature • Size • Mass

  10. ASTROPHYSICS Caroline Chisholm College Physics 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. ASTROPHYSICS Caroline Chisholm College Physics Gather, analyse information and use available evidence to assess the impact of increased knowledge in astrophysics on society • 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 WHY STUDY ASTROPHYSICS? • 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 aaawww! it's over!

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