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 ..........................................................................................................................