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]
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