stars

• what is the 1st stage of a star? (stage 1)

  nebula
• what is a nebula? (stage 1)


  a big cloud of dust and gas
• what happens to the nebula over time? (stage 1)

  the attractive force of gravity pulls the dust and gas together to form a protostar
• what is the 2nd stage of a star? (stage 2)

  protostar
• what happens to the protostar? (stage 2)

  1. as more particles collide and join the protostar it gets bigger and its gravity gets stronger.
  2. this allows it to attract even more dust and gas.
  3. the gravity squeezes the protostar making it more dense.
  4. this means the particles inside it collide more often.
  5. this raises the temperature of the protostar
  6. when the temperature gets high enough, hydrogen and nuclei start to fuse together to form helium nuclei (nuclear fusion)
  7. this gives out huge amounts of energy which keeps the core of the star hot
  8. at this point we call it a main sequence star
• what is the 3rd stage of a star? (stage 3)

  the main sequence star (the actual star)
• what is the outward pressure in the main sequence star caused by? (stage 3)


  all the energy
• what is the outward pressure balanced by in the main sequence star? (stage 3)

  the inward pressure. this allows for a long stable period that can last for billions of years.
• what is the inward pressure of the main sequence star caused by? (stage 3)

  gravity
• what stage is our sun currently in?

  the main sequence star
• what does it mean when the star starts to run out of hydrogen? (stage 3)

  the star won't be able to do nuclear fusion so the inward pressure of gravity takes over an contracts the star into a small ball
• what happens when the star is in a small ball? (stage 3)

  the star becomes so hot and dense that nuclear fusion can start up again which will cause it to expand again
• what does the nuclear fusion form this time instead of just forming helium? (stage 3)

  forms heavier elements
• what does how much the star expands depend on? (stage 3)

  how big the initial star was
• what will happen to the main sequence star if its small/medium? (stage 3)

  it will form a red giant
• what will happen to the main sequence star if it was a really big star? (stage 3)

  it will form a red super giant
• how long does it take for the red giant to become unstable? (red giant)


  a relatively short amount of time
• what happens when the red giant becomes unstable? (red giant)


  it expels its outer layers of dust and gas, which leave behind a hot, dense, solid core (which doesn't do any nuclear fusion)
• what is the hot, dense, solid core that is left behind when the red giant becomes unstable? (red giant)

  the white dwarf
• why do we call it the white dwarf? (white dwarf)

  • gives off lots of light so it appears white
  • relatively small
• what happens to the white dwarf over time? (white dwarf)

  gets cooler and darker as it emits all of it energy. it then transitions to a black dwarf because it no longer has energy to emit light.
• why do red super giants start to shine brightly again? (red super giant)

  because they undergo more nuclear fusion
• what eventually happens to the red super giant? why? (red super giant)

  after several cycles of expansion and contraction they eventually explode into a supernova
• what does a supernova do? (supernova)

  forms elements heavier than iron that are ejected across the universe
• what will happen if the red super giant was very big? (supernova)

  it will condense into a very dense core called a neutron star
• what will happen if the red super giant was absolutely massive? (supernova)

  it might collapse in on itself and become a black hole
• why do we call them a black hole? (black hole)

  because they are so dense that gravity is able to pull in any light that passes nearby which means they appear and tiny hoels in the universe where no light is ever emitted
• name each stage of the life cycle of stars?

  • dust and gas
  • protostar
  • main sequence star
  • either a red giant or red super giant
  • red giant: white dwarf -> black dwarf
  • red super giant: supernova -> neutron star or black hole