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Stars & Galaxies



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  • 1. Stars & Galaxies
  • 2. History of the universe
    • 13 billion years ago – Big Bang
    • A tenth of a second later – Quarks + electrons form.
    • Minutes later – Quarks combine to form nucleons (protons & neutrons)
    • 100,000 years later – Neutrons, protons + electrons combine to form simple neutral atoms of hydrogen + helium.
    • Billions of year later – hydrogen + helium atoms are pulled together by gravity and form the first stars and galaxies.
    • Universe continues to expands moving stars and galaxies further apart.
  • 3.  
  • 4. The Milky Way
  • 5. The Milky Way
  • 6. Life Cycle of a Star
  • 7. Protostar
    • Gravity causes matter in clouds of gas to clump together and form a protostar.
    • The protostar continues to be pulled together by gravity and becomes denser.
    • Hydrogen atoms get pulled so close they fuse together to form helium.
    • This nuclear fusion process produces heat and star begins to emit light.
  • 8. Main Stage
    • Star is in equilibrium for billions of years as the supply of hydrogen undergoes fusion.
    • The outwards force of the radiation exactly balances the inwards force of gravity so the star remains the same size.
  • 9. Red Giant
    • As the hydrogen starts to run out the star cools down, expands and turns red.
    • It is now known as a red giant.
    • At this stage helium atoms themselves begin to fuse and heavier more complicated elements are created.
  • 10. White Dwarf
    • When the supply of hydrogen runs out nuclear fusion stops.
    • Gravity is now able to collapse the star in further since the force of the emitted radiation has disappeared.
    • It heats up and its colour changes from red>yellow>white
  • 11. Death of a Star
    • What happens next depends on the mass of the star.
    • ?
  • 12. Low mass white dwarfs
    • White dwarfs with a low mass cool down gradually.
    • As they cool they stop emitting light.
    • They become known as black dwarfs.
  • 13. High mass white dwarfs
    • Gravity continues to collapse the star.
    • It suddenly explodes in an event know as supernova and ejects material into space.
    • The remaining/left behind material collapses under gravity into a neutron star.
    • The neutron star has an extremely high density similar to that of an atomic nucleus.
    • It is composed entirely from neutrons with no space between them.
    • (unlike normal matter that has a lot of empty space between the nucleus and orbiting electrons.
  • 14. Supernova
  • 15. Neutron Star
  • 16. Black Holes
    • If the neutron star has a large enough mass it will continue to collapse even further and become a black hole.
    • The black hole has a mass occupying a single point (i.e. 0 volume) and an will therefore have an infinite density.
    • Gravity is so strong nothing can escape its gravitational field (this includes light).
  • 17. gravity large star small star nuclear fusion super- nova nebulae Life cycle of a star
  • 18.