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I always thought the only fuel for a star was hydrogen, which is fused into helium.

But while reading some questions and answers here in ASO, I saw phrases like "This balance stays relatively stable until the star runs out of whatever its current fuel is".

Besides hydrogen, what are the possible fuels in a star’s core?

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As a star begins to age and exhaust its hydrogen supply, pressure will build in its interior until temperatures rise enough to begin fusing helium into carbon. If the star is massive enough, this process will continue, using heavier elements each time.

Referring to this link on stellar fusion, depending on their mass, stars use a variety of elements from hydrogen to silicon as 'fuel'. Stellar cores of stars towards the end of their giant stages will have cores of iron, but iron doesn't fuse into anything heavier in a stellar core.

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    $\begingroup$ Iron doesn't ever fuse into anything heavier as a fuel, since fusing into heavier elements absorbs energy rather than creates it. But in things like supernovae, the vast amount of energy around can produce heavier elements, but this diminishes rather than increases the explosion. $\endgroup$ – Mark Olson Jun 21 '18 at 13:39
  • $\begingroup$ So, every star begins with a hydrogen nucleus and as the time goes by, it can turn to heavier elements if have the right amount of pressure? $\endgroup$ – Max Jun 21 '18 at 14:15
  • $\begingroup$ @Max Broadly speaking, yes. $\endgroup$ – user10106 Jun 21 '18 at 14:56
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Stars can consume everything as fuel in the periodic table up to iron, which is endothermic.

When they consume other elements different from Hydrogen, their radiation pressure gets higher and the star expands its volume, sometimes even it surpasses the gravitation force of the star and starts to lose material.

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    $\begingroup$ Lots of places seem to equate fusion with radiation pressure, but radiation pressure only matters in the highest luminosity stars. For normal stars, gas pressure is all that matters. $\endgroup$ – Ken G Jun 22 '18 at 12:06
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Stars use pretty much every element from Hydrogen to Iron as fuels. The three main ones are Hydrogen, Helium and Carbon. Hydrogen is a light element so it produces much energy as it fuses into deuterium or Helium. The heavier the element is the less energy it produces. Heavier element shortens the supply of fuels as the rate of reaction keeps on increasing. For example Carbon takes 600 years to fuse into neon and silicon takes one day to fuse into Iron. After iron it just becomes counter efficient for the star to fuse it into heavier elements as it would need more energy to fuse into heavier elemnets than they would produce. So after iron it comes to a slow stop.So anyting from hydrogen to iron could be use as fuel Reference: http://abyss.uoregon.edu/~js/ast122/lectures/lec18.html

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  • $\begingroup$ Not necessarily "to" iron. By atomic number, any element before iron. $\endgroup$ – Brayden Fox Jul 4 '18 at 23:08

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