Transcript for:
Understanding Star Life Cycles

Hi guys welcome to let's get to the marks today  we're looking at the life cycle of stars as it's   known in AQA GCSE or Stellar Revolution as it's  known in IGCSE physics both cover the same content   so don't worry which you're doing here before you  you see dust and gas in the far reaches of the   universe coalescing together to form stars in this  presentation we're going to go through all the   stages in a star's life stage one Stars initially  form from clouds of dust we call these nebula here in the second stage the dust and gas  particles from the nebula are pulled together   by gravity particle collision causes a rise  in temperature eventually the heat is high   enough for nuclear fusion to take place this  is where hydrogen nuclei slammed together at   tremendous speed to form a helium nuclei  and release tremendous amounts of energy   this energy forms a hot core and a protostar  is born so the second stage of a star's life   is the formation of a protostar the third stage  of a star's life the longest stage is called   the main sequence normally the stage lasts for  billions of years but in very big stars they burn   through the fuel quickly and their main sequence  is shorter as you see here in this picture we're   going to look at why the star doesn't collapse or  doesn't expand why is it stable for a long period   well the nuclear fusion in the star's core creates  an outward pressure shown here by the black arrows   this outward pressure is equaled by the  gravitational attraction trying to collapse   the star therefore as these arrows are equal the  star neither collapses or expands it stays stable foreign the fourth stage of a star's life the  hydrogen in the core begins to run out this   means there's less nuclear fusion in the core and  the outward pressure shown by the black arrows is   smaller it's now outweighed by the gravitational  force of attraction shown here with the green   arrows this means the star begins to collapse  as it shrinks it has a smaller volume so it   heats up it then expands its outer layers  becoming something we know as a red giant in this fourth stage is where we get the  Divergence between Stars the same size as   our sun and supermassive Stars the Stars the same  size as our sun become red giants and stars much   bigger than our sun become super red giants  during this phase the star is cooler hence   its red color which is of a lower frequency than  the color blue or violet the star has run out of   hydrogen and so is forced to fuse helium it  can force elements all the way to iron and   the Elements shown here circled in red are the  elements Stars can form in the red giant phase the fifth stage for stars are sun size   they now eject their outer layers and leave behind  a dense core they are now called a white dwarf although only theoretical at this time  it is believed that stars like our sun   when they're in the white dwarf phase  they will call down and stop emitting   light altogether at this point  they will become black Dwarfs   however the universe is not old enough yet for any  of its stars to have reached the black dwarf phase for stars much bigger than our sun there  is a totally different fate awaiting   for massive stars the fifth stage results  in an explosion called the supernova   during this explosion elements heavier  than iron will be formed from Fusion   and these elements will go on to  form new planets and new stars   elements like silver and gold are formed in  these final stages of a massive star's life in the final stage of a massive star's life  it will form a dense neutron star or a super   dense object we call a black hole a black  hole has such a strong gravitational pull   that even light cannot Escape a neutron star  is not quite as dense but it is still dense   enough that the gravitational pull will pull  the electrons from the orbitals of its atoms   into its nuclei and fuse with the protons forming  neutrons a neutron star is purely made of neutrons okay we're now going to look at the overall map  of the star's life you need to learn this off by   heart for your exams it could welcome up in your  Physics Exam either for AQA or IGCSE at Excel   we can see here that the stages of a star's  life are exactly the same stage one two and   three for both supermassive stars and stars  the size of our sun but it's at stage four when   they enter the red giant or super red giant  that their lives Go in different directions   so what's going to happen now you're going to get  a series of exam questions on this presentation   these are taken from real exam papers so pause  the video when the question comes up have a go   and then unpause to check your answers all right  guys that's all from me let's get to the marks [Music] [Music]

[Music] [Music] [Music]