star life cycle

• stars initially formed from...

  a cloud of dust and gas called a nebula - the force of gravity pulls the dust and gas together to form a protostar
• as the star gets denser...

  the temperature rises and more particles collide with with each other
• when the temperature of the protostar gets high enough...

  hydrogen nuclei undergo nuclear fusion to form helium nuclei
• what does nuclear fusion do in a protostar?

  give out huge amounts of every, which keeps the core of the sun hot - a star is born from this
• what happens in the stable period of a star?

  the outward pressure caused by nuclear fusion that tried to expand the star balances the force of gravity pulling everything inwards - here the star is called the main sequence star
• what happens when the hydrogen of a star begins to run out?

  the star swells into a red giant (if it is a small star) or a super red giant (if it's a larger star) and the surface cools. fusion of helium (and other elements) occurs and heavier elements (up to iron) are created in the core of the star
• what happens to a smaller sized star once hydrogen runs out?

  it becomes unstable and ejects its outer layer of dust and gas together- this leaves behind a a white dwarf, a hot, dense, solid core
• as a white dwarf cools down...

  it emits less and less energy and when it no longer emits a significant amount, it is called a blank dwarf as it can no longer make large amounts of heat and light
• what happens to a bigger sized star once hydrogens runs out?

  it becomes to grow brightly again as they undergo more fusion and expand and contract several times, forming elements as heavy as iron and 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 stars
• what does an exploding supernova leave behind?

  a very dense core called a neutron star after throwing the outer layers of dust and gas into space. if the star is massive enough, it will become a black hole - a super dense point in space that not even light can escape from
• stars and their life cycles produce and distribute...

  all naturally occurring elements
• nebula


  a large cloud of dust and gas in space
• protostar


  a contracting cloud of gas and dust with enough mass to form a star; the earliest stage of a star's life
• main sequence star


  any star that is fusing hydrogen in its core and has a stable balance of outward pressure from core nuclear fusion and gravitational forces pushing inward
• red giant


  a star that expands and cools once it runs out of hydrogen fuel
• white dwarf


  stage in which a star has used up its helium and its outer layers of dust and gas escape into space, leaving behind a hot, dense core that contracts
• black dwarf


  star that results when a white dwarf stops giving off energy
• red super giant


  a big star will swell into one of these and fusion of helium occurs, and elements less heavy than iron (and iron) are created in the core
• supernova


  a star that suddenly increases greatly in brightness because of a catastrophic explosion that ejects most of its mass into the universe
• neutron star


  a star that has collapsed under gravity to the point that the electrons and protons have smashed together to form neutrons
• black hole


  an object in space having a gravitational field so intense that no matter or radiation can escape