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• Stars


  Massive, glowing balls of extremely hot gas (plasma) in space
• After the Sun, the nearest star is Proxima Centauri. It is 4.3 light years away, which is about 41 million, million km away!
• Nuclear fusion


  The process that powers a star
• The outward force generated by the fusion process is balanced by the inward pull of the star's gravity
• Nebulae


  Huge clouds of gas and dust, sometimes known as 'stellar nurseries' or 'star forming regions'
• Stellar ignition


  1. When a star starts to shine

  2. When a star can fuse H into He
• 7 main stages of a star

  • Giant Gas Cloud
  • Protostar
  • T-Tauri Phase
  • Main Sequence
  • Red Giant
  • The Fusion of Heavier Elements
  • Supernovae and Planetary Nebulae
• Main sequence


  The stage in development where the core temperature reaches the point for the fusion to commence, where protons of hydrogen are converted into atoms of helium
• Main-sequence stars are fusing hydrogen into helium. These nuclear fusion take place deep in the cores of stars. Stars spend about 90% of their lives in this stage
• Gravity


  The force that holds us on Earth, keeps planets in orbit around stars and stars in orbit around the centre of our galaxy
• Hydrostatic equilibrium


  The balance between outward pressure and inward pull
• Supergiants


  • Have the largest radius of all known stars
  • Evolve from large main-sequence stars
  • Can contain 8 - 200 times the mass of the Sun
  • Can be as bright as a million Suns
  • Can be red or blue in colour
• The star Betelgeuse in the constellation of Orion is a red supergiant. Blue supergiants are much hotter
• Planetary nebula phase


  A final stage in a low-mass star's life, where the star sheds its outer layers
• White dwarf


  A bright, hot, compact star about the same size, in terms of volume, as the Earth
• Brown dwarfs


  Very dim, glowing objects where the temperatures and pressures deep within were never high enough for nuclear fusion to start
• Supernovae


  Huge explosions in space that take place during the final stages of some stars' lives, where one supernova can briefly shine brighter than a whole galaxy
• Type Ia supernovae


  Thermonuclear supernovae that occur in a binary (or double) star system where one of the two stars is a white dwarf
• Accretion


  The process where a white dwarf gets more and more massive as it pulls in material from its companion star
• Electron degeneracy pressure


  Stops the white dwarf from collapsing, as the electrons inside each atom repel each other and prevent the white dwarf from shrinking any further
• Chandrasekhar limit


  The mass limit above which a white dwarf cannot remain stable
• Neutron star


  The collapsed core of a massive star, left behind after a supernova explosion
• Pulsar


  A dense, rotating object which gives off a beam of radiation from each of its magnetic poles, coming from neutron stars
• The first pulsar was discovered in 1967 by Jocelyn Bell Burnell and Antony Hewish, who at first thought the regularly repeating radio signal could be from aliens
• Black hole


  An incredibly small, dense object that forms after a supernova, where anything left of the star is squashed and compacted
• Event horizon


  The distance at which light cannot escape from a black hole
• Gamma-ray bursts (GRBs)


  Very short and intense bursts of gamma-ray radiation, higher in energy than X-rays
• Short gamma-ray bursts


  GRBs which last for less than 2 seconds, with a mean average duration of 0.2 seconds
• Long gamma-ray bursts


  GRBs which last for more than 2 seconds, making up about 70% of the total number observed
• Stellar Classification


  • O
  • B
  • A
  • F
  • G
  • K
  • M
• Hotter 'O' stars glow bluer and cooler 'M' stars glow redder. Our closest star, the Sun, shines with a yellow light and is classed as a 'G' star, with a temperature of about 5,800 °K
• Hertzsprung-Russell diagram


  Shows the relationship between a star's temperature and its luminosity, also called the H-R diagram or colour-magnitude diagram
• Variable stars


  Stars that appear to change brightness (as seen from Earth) over time, due to changes in the amount of energy they emit
• 4 common types of Variable Stars

  • Cepheid Variables
  • RR Lyrae variable stars
  • Mira variable stars
  • Eclipsing binary
• Cepheid Variables


  Yellow, giant stars which pulsate, causing the star to swell and shrink in a regular, repeating way
• RR Lyrae variable stars


  Like Cepheids but far dimmer, often part of globular clusters
• Mira variable stars


  Cool supergiants which are also pulsating, with large variations in brightness over many months
• Eclipsing binary


  A system which contains two stars orbiting in a plane in line with our view, so that both stars will block out light from the other at some point during the orbit
• 3 basic types of star clusters

  • Globular Clusters
  • Open Clusters
  • Stellar Associations
• Globular Clusters


  Nearly symmetrical round systems of, typically, hundreds of thousands of stars