Yep, mostly hydrogen… with a little helium… and a little less of the heavier elements… but it depends…
In fact it is possible to say fairly precisely what elements are present simply by looking carefully at the UV-visible spectrum of a star. Each element absorbs light in quite distinct ways (at particular wavelengths) and they leave dark lines in the spectrum of light coming from the star that we can observe.
So, it turns out we can say fairly confidently that at the beginning of a star’s life it is almost entirely hydrogen (depending where it was formed and what gasses were actually around). As it ages the hydrogen is ‘burnt’ in fusion reactions to produce heavier elements. Our star might end up ‘burning’ elements up to carbon and then will have to stop (it gets more difficult to burn heavier elements, you get less energy out). At which point it will have a very different composition to what it started with. (It will then die by suddenly expanding, throwing off its outer layers to be left with a very hot, fairly carbon rich, core…. which will then slowly cool)
More massive stars can burn heavier elements all the way to iron… but even the heaviest has to stop there. Fusing iron atoms together does not produce energy at all, rather it requires energy to be put in. These stars then also die but (depending on the initial mass) rather more dramatically than our star, with a large explosion (which compresses the outer layers of the star to form the elements heavier than iron) to leave neutron stars or black holes.
So, in fact ‘what stars are made out of’ changes throughout their lives.
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Ian commented on :
Yep, mostly hydrogen… with a little helium… and a little less of the heavier elements… but it depends…
In fact it is possible to say fairly precisely what elements are present simply by looking carefully at the UV-visible spectrum of a star. Each element absorbs light in quite distinct ways (at particular wavelengths) and they leave dark lines in the spectrum of light coming from the star that we can observe.
So, it turns out we can say fairly confidently that at the beginning of a star’s life it is almost entirely hydrogen (depending where it was formed and what gasses were actually around). As it ages the hydrogen is ‘burnt’ in fusion reactions to produce heavier elements. Our star might end up ‘burning’ elements up to carbon and then will have to stop (it gets more difficult to burn heavier elements, you get less energy out). At which point it will have a very different composition to what it started with. (It will then die by suddenly expanding, throwing off its outer layers to be left with a very hot, fairly carbon rich, core…. which will then slowly cool)
More massive stars can burn heavier elements all the way to iron… but even the heaviest has to stop there. Fusing iron atoms together does not produce energy at all, rather it requires energy to be put in. These stars then also die but (depending on the initial mass) rather more dramatically than our star, with a large explosion (which compresses the outer layers of the star to form the elements heavier than iron) to leave neutron stars or black holes.
So, in fact ‘what stars are made out of’ changes throughout their lives.
358chea24 commented on :
There are so many stars in the world. Stars fill the sky almost every night and I didn’t realise that they were burning balls of gas!