topic 8

• how does a star start off?

  as a cloud of dust and gas (nebula)
• what is the life cycle of a star the same size as the sun?

  a cloud of dust and gas(nebula)-> protostar -> main sequence star -> red giant -> white dwarf -> black dwarf
• what is the life cycle of a star which is bigger than the sun?

  a cloud of dust and gas (nebula) -> protostar -> main sequence sun -> red super giant -> super nova -> neutron star or black hole
• how does the star move from a nebula to a protostar?

  the force of gravity pulls the dust and gas together to form a protostar. the temperature rises and the star becomes denser and more particles collide. when the temperature gets high enough hydrogen nuclei undergo nuclear fusion to form helium nuclei.
• what is the main sequence star?

  it enters a long stable period where the outward pressure from the nuclear fusion that tries to expand the star balances the force of gravity pulling everything inwards
• what happens when the main sequence star goes to a red giant or a red super giant?

  the hydrogen begins to run out. it then expands to form a red giant or red super giant. it becomes red as the surface cools. fusion of the helium occurs
• how does a white dwarf happen?

  the small star becomes unstable and ejects the outer layer of dust and gas which leaves behind the dense hot solid core - the white dwarf
• how is the black dwarf formed?

  as the white dwarf cools it emits less energy and when it no longer emits a significant amount - black dwarf
• how is a supernova formed?

  the big stars glow brightly as they undergo more fusion, they will then explode in a supernova which forms elements, ejecting them to the universe to form new planets and stars
• how is a neutron star and black hole formed?

  the exploding supernova throws the outer layers of dust and gas which eaves the dense core - neutron star. if the star is massive enough it will become a black hole
• what orbits the sun in our solar system?

  planets, moons and artificial satellites
• what is our solar system called?

  The Milky Way
• gravity provides the force that creates orbits
• if an object is orbiting in a circle it is constantly changing direction and accelerating
• there is a force acting on the object orbiting directed towards the centre of the circle
• the closure u get to a star or planet the stronger the gravitational force
• would an object orbiting the a planet or star closer be moving fast or slower?

  faster
• what is red shift?

  The shift of light towards longer wavelengths due to the expansion of the universe.
• more distant galaxies have greater red shifts meaning they are moving away faster than nearer ones
• what is the Big Bang theory?

  • initially all the matter in the universe occupied a very small space which was very dense and hot
  • then it exploded - space started expanding
• dark matter is the name given for an unknown substance which holds galaxies together
• dark energy is thought to be responsible for the accelerated expansion of the universe