P8

• Formation Of A Star

  • initially form from a cloud of dust and gas called a nebula
  • force of gravity pulls the dust and gas together to form a protostar
  • the temperature rises as the star gets denser and more particles collide with each other
  • when the temperature gets high enough, hydrogen nuclei undergo nuclear fusion to form a helium nuclei
  • this gives out huge amounts of energy, which keeps the core of the star hot
  • a star is created
• Main Sequence Star

  • the star enters a long stable period where the outward pressure caused by the nuclear fusion that tries to expand the star balances the force of gravity pulling everything inwards
  • typically lasts several billion years
• Red Giants/Super Red Giants

  • eventually hydrogen begins to run out
  • the star then swells into a red giant if it's a small star or a red super giant if it's a large star
  • it becomes red and the surface cools
  • fusion of helium and other elements occurs
  • heavier elements (up to iron) are created in the core of the star
• White Dwarf

  • a small-medium sized star then becomes unstable and ejects it's outer layer of dust and gas
  • this leaves behind a hot, dense solid core - a white dwarf
• Black Dwarf

  • as a white dwarf cools down, it emits less and less energy
  • when it no longer emits a significant amount, it is called a black dwarf
• Supernova

  • big stars start to glow brightly again as they under go more fusion and expand and contract several times, forming elements as heavy as iron in various nuclear reactions
  • eventually they'll explode in a supernova, forming elements heavier than iron and ejecting them into the universe to form new planets and star
• Neutron Star

  • exploding supernova throws the outer layers of dust and gas into space, leaving a very dense core called a neutron star
  • if the star is massive enough, it will become a black hole
• Life Cycle Of A Star

  • nebula
  • protostar
  • main sequence star
  • red giant -> white dwarf -> black dwarf
  • red super giant -> supernova -> neutron star/black hole
• Solar system is all the stuff that orbits our sun, including:

  • Planets
  • Dwarf Planets
  • Moons
  • Artificial Satellites
• Planets

  • large objects that orbit a star
  • 8 in our solar system
  • they have to be large enough so that their gravity is strong enough to have pulled in any nearby objects
• Dwarf Planets

  • planet-like objects that orbit stars, but don't meet all of the rules for being a planet
• Moons

  • orbit planets
  • type of natural satellite
• Artificial Satellites

  • satellites that humans have built
  • generally orbit the earth
• • the planets move around the sun in circular orbits
  • if an object is travelling in a circle it's constantly changing direction, meaning it's constantly accelerating and changing velocity
  • for an object to accelerate, there must be a force acting on it. This force is directed towards the centre of the circle
  • the force causes the object to change it's direction
  • the object keeps accelerating towards what it's orbiting but the instantaneous velocity keeps it travelling in a circle
  • the force that makes this happen is provided by the gravity between the planet and the sun
• • the closer you get to a planet, the stronger the gravitational force is
  • the stronger the force, the faster the orbiting object needs to travel to remain in orbit
  • for an object in a stable orbit, if the speed of the object changes, the size of it's orbit must do so too. Faster moving objects will move in a stable orbit with a smaller radius than slower moving ones
• Red-shift

  There is an observed increase in the wavelength of light from most distant galaxies. The further away the galaxies, the faster they are moving and the bigger the observed increase in wavelength.
• Red-shift provides evidence that the universe is expanding because it suggests the source of light is moving away from us. Measurements of red-shift indicates that these distant galaxies are moving away from us very quickly
• More distant galaxies have greater red-shifts than nearer ones, meaning more distant galaxies are moving away faster than nearer ones
• Big Bang Theory

  • initially all the matter in the universe occupied a very small space
  • the tiny space was very dense and so very hot
  • then it 'exploded'
  • space started expanding, and it still is
• observations of supernovae from 1998 to the present day appear to show that distant galaxies are moving away from us faster and faster
• Currently scientists think the universe is mostly made up of dark matter and dark energy. But no one really knows what these things really are so there are lots of different theories about it
• Dark matter is the name of the unknown substance which holds galaxies together, but doesn't emit any electromagnetic radiation
• Dark energy is thought to be responsible for the accelerated expansion of the universe