Stars & Galaxies


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Stars & Galaxies

  1. 1. Stars & Galaxies
  2. 2. History of the universe <ul><li>13 billion years ago – Big Bang </li></ul><ul><li>A tenth of a second later – Quarks + electrons form. </li></ul><ul><li>Minutes later – Quarks combine to form nucleons (protons & neutrons) </li></ul><ul><li>100,000 years later – Neutrons, protons + electrons combine to form simple neutral atoms of hydrogen + helium. </li></ul><ul><li>Billions of year later – hydrogen + helium atoms are pulled together by gravity and form the first stars and galaxies. </li></ul><ul><li>Universe continues to expands moving stars and galaxies further apart. </li></ul>
  3. 4. The Milky Way
  4. 5. The Milky Way
  5. 6. Life Cycle of a Star
  6. 7. Protostar <ul><li>Gravity causes matter in clouds of gas to clump together and form a protostar. </li></ul><ul><li>The protostar continues to be pulled together by gravity and becomes denser. </li></ul><ul><li>Hydrogen atoms get pulled so close they fuse together to form helium. </li></ul><ul><li>This nuclear fusion process produces heat and star begins to emit light. </li></ul>
  7. 8. Main Stage <ul><li>Star is in equilibrium for billions of years as the supply of hydrogen undergoes fusion. </li></ul><ul><li>The outwards force of the radiation exactly balances the inwards force of gravity so the star remains the same size. </li></ul>
  8. 9. Red Giant <ul><li>As the hydrogen starts to run out the star cools down, expands and turns red. </li></ul><ul><li>It is now known as a red giant. </li></ul><ul><li>At this stage helium atoms themselves begin to fuse and heavier more complicated elements are created. </li></ul>
  9. 10. White Dwarf <ul><li>When the supply of hydrogen runs out nuclear fusion stops. </li></ul><ul><li>Gravity is now able to collapse the star in further since the force of the emitted radiation has disappeared. </li></ul><ul><li>It heats up and its colour changes from red>yellow>white </li></ul>
  10. 11. Death of a Star <ul><li>What happens next depends on the mass of the star. </li></ul><ul><li>? </li></ul>
  11. 12. Low mass white dwarfs <ul><li>White dwarfs with a low mass cool down gradually. </li></ul><ul><li>As they cool they stop emitting light. </li></ul><ul><li>They become known as black dwarfs. </li></ul>
  12. 13. High mass white dwarfs <ul><li>Gravity continues to collapse the star. </li></ul><ul><li>It suddenly explodes in an event know as supernova and ejects material into space. </li></ul><ul><li>The remaining/left behind material collapses under gravity into a neutron star. </li></ul><ul><li>The neutron star has an extremely high density similar to that of an atomic nucleus. </li></ul><ul><li>It is composed entirely from neutrons with no space between them. </li></ul><ul><li>(unlike normal matter that has a lot of empty space between the nucleus and orbiting electrons. </li></ul>
  13. 14. Supernova
  14. 15. Neutron Star
  15. 16. Black Holes <ul><li>If the neutron star has a large enough mass it will continue to collapse even further and become a black hole. </li></ul><ul><li>The black hole has a mass occupying a single point (i.e. 0 volume) and an will therefore have an infinite density. </li></ul><ul><li>Gravity is so strong nothing can escape its gravitational field (this includes light). </li></ul>
  16. 17. gravity large star small star nuclear fusion super- nova nebulae Life cycle of a star