Session 20 Astrophysics

Session 20 Astrophysics Sarah Symons, Naomi Banks, Cheryl Hurkett, Derek Raine Physics Innovations Centre for Excellence in Learning and Teaching CETL (Leicester) Department of Physics and Astronomy University of Leicester 1 Contents Welcome .................................................................................................................................. 6 Session Author.................................................................................................................... 6 Positional Astronomy ........................................................................................................... 7 Learning Objectives ........................................................................................................... 7 The Problem ........................................................................................................................ 7 Pan and tilt .......................................................................................................................... 8 Altitude and azimuth ........................................................................................................ 9 The Pole Star ..................................................................................................................... 10 At the north pole .............................................................................................................. 11 To warmer climates ......................................................................................................... 12 Terrestrial coordinates ..................................................................................................... 14 Celestial coordinates (RA, dec) ...................................................................................... 15 Seasons ............................................................................................................................... 16 Equatorial tripod .............................................................................................................. 17 Summary ........................................................................................................................... 18 SAQs .................................................................................................................................. 19 Answers ............................................................................................................................. 20 Stars ....................................................................................................................................... 21 Learning Objectives ......................................................................................................... 21 The Problem ...................................................................................................................... 21 Star Formation ........................................................................................................................... 21 The Hertzsprung-Russell or H-R Diagram ............................................................................ 22 2 Stellar Structure – Holding it up .................................................................................... 24 The flow of energy ........................................................................................................... 25 Energy generation ..................................................................................................................... 26 Explaining the H-R diagram .......................................................................................... 27 Energy generation ............................................................................................................ 28 The pp chain .............................................................................................................................. 28 The CNO cycle ........................................................................................................................... 28 Star death: What happens when the energy runs out? ............................................. 30 Formation of the elements .............................................................................................. 32 Final stages ........................................................................................................................ 33 Summary ........................................................................................................................... 34 SAQs .................................................................................................................................. 34 Answers ............................................................................................................................. 35 The Violent Universe ......................................................................................................... 36 Learning Objectives ......................................................................................................... 36 Novas ................................................................................................................................. 36 Supermassive black holes ............................................................................................... 39 Types of ‚active galactic nuclei‛ .................................................................................... 40 Gamma Ray Bursts .......................................................................................................... 42 Energy scale ...................................................................................................................... 43 Why are gamma ray bursts of interest? ........................................................................ 45 Types of Gamma Ray Bursts .......................................................................................... 45 The structure of a gamma ray burst .............................................................................. 46 How are the gamma-rays produced? ............................................................................ 48 Synchrotron Radiation ............................................................................................................. 48 3 Inverse Compton Scattering. ................................................................................................... 49 Non-Thermal Radiation ........................................................................................................... 50 Summary ........................................................................................................................... 51 SAQs .................................................................................................................................. 52 Answers ............................................................................................................................. 53 Cosmology ............................................................................................................................ 54 Learning Objectives ......................................................................................................... 54 The Start of Cosmology ................................................................................................... 54 Sir William Herschel and the Galaxy ............................................................................ 56 Hubble determines the size of the Universe ................................................................ 56 The visible Universe ........................................................................................................ 58 The distribution of galaxies on large scales ................................................................. 59 The expanding Universe ................................................................................................. 59 The expansion of the Universe ....................................................................................... 61 Models of the Universe ................................................................................................... 62 The Cosmic Microwave Background radiation ........................................................... 63 Dark Matter and Dark Energy ....................................................................................... 65 Nucleosynthesis ............................................................................................................... 69 Formation of Helium in the Early Universe ................................................................. 69 Where do the neutrons come from? .............................................................................. 70 Abundances of the light elements ................................................................................. 71 Propagation of radiation ................................................................................................. 72 The Horizon Problem ...................................................................................................... 72 Inflation ............................................................................................................................. 73 The future .......................................................................................................................... 74 4 Summary ..........................................................................................................................

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