• Question: What happens when stars run out of fuel, and w hat do you mean by fuel?

    Asked by to Dave on 17 Jun 2014. This question was also asked by .
    • Photo: Dave Jones

      Dave Jones answered on 17 Jun 2014:

      Stars are made mainly of Hydrogen. They shine because they are burning that Hydrogen, turning it into Helium by a process called nuclear fusion. Hydrogen is their main fuel. When they run out of Hydrogen, some stars (if they are heavy enough) can briefly burn Helium, turning it into heavier elements like Carbon, Nitrogen and Oxygen. But when that has run out as well, they have officially run out of fuel, which is not good news for the star. At that point, one of two things happen. If they are really heavy (more than 8x the mass of the Sun), they explode as a supernova, a type of massive nuclear explosion. But, most stars aren’t massive enough for this, most stars are like the Sun. Those stars will gently puff off their outer layers, just leaving behind a core made from the left over Carbon and Oxygen from before. This hot core will then spend billions of years not really doing anything except cooling down really, really slowly.

Comments

  • sarahhedley commented on :

    wow! That’s interesting! What are stars made of though? If it is hydrogen then won’t all the particles just be floating around, but if it is a solid then how do the gasses burn?

    • Photo: Laurence

      Laurence commented on :

      The stars are mostly made of hydrogen. The reason why the gas particles don’t fly all over the place is that there is SO MUCH gas that the gravity attracting all the particles is way too strong for them to float around like a gas would do on the surface of the Earth. In fact, the gravity is SO strong and it compresses the gas SO much that the gas doesn’t remain a gas, it becomes a plasma!! A plasma is a very high temperature state of matter (just like solid, liquid and gas are different states, plasma is a state that simply has higher energy than gas!). That’s why the sun appears like a solid ball of fire as opposed to a transparent cloud of gas, because it’s a burning hot ball of plasma!

      You probably have already seen plasma on Earth, actually. Lightning bolts are actually made of plasma, and the same goes with Neon lights, inside the bulb it’s not gas, it’s actually plasma 😀 !!

  • Photo: Aimee

    Aimee commented on :

    @sarahhedley the stars are made up mostly of hydrogen, but they are all held together by the gravity of there being so much of it!
    The hydrogen at the centre of the Sun collided with other hydrogen, hopefully with high enough energy to fuse together to form helium (because helium is heavier, it sinks to the middle of the Sun).
    Did you know it actually takes thousands of years for the energy from this fusion to get out of the surface of the Sun!