• Question: what is the life cycle of a star? and why do they shine?

    Asked by simmy123 to Amy, Grant, Martin, Shawn, Usman on 15 Mar 2013.
    • Photo: Grant Kennedy

      Grant Kennedy answered on 15 Mar 2013:

      That’s a huge story to tell…here’s a very short version: Basically you start with a big cloud of gas and dust, which can collapse down to make a star. When the star has collapsed enough it gets really hot and dense in the middle and nuclear fusion can happen, which “burns” Hydrogen to heavier elements like Helium and Carbon. It’s the energy from nuclear fusion that gives them the energy to shine. Eventually the Hydrogen runs out, the the might then burn Helium, but eventually the Helium runs out too. When the fuel has run out the star expands, and if it’s massive enough can explode in a supernova. Other stars just blow their mass off. The final stages are black holes, neutron stars, and white dwarves (crazy names I know).
      g

    • Photo: Amy Tyndall

      Amy Tyndall answered on 19 Mar 2013:

      For a star the same size as our Sun, it takes about 12 billion years, and roughly goes:

      Protostar: Giant cloud of hydrogen starts to collapse to form a new, baby star

      Main sequence star: Hydrogen starts to fuse into helium, the star stops collapsing and gravity balances it out – the ‘real’ star is born! 90% of the star’s life is in this phase.

      Red Giant: The core of the star starts to run out of hydrogen, but in the outer layers the hydrogen continues to fuse into helium. Without the reaction in the core, the overall effect of gravity is weaker, so the star expands to become a huge red giant star. It stays a red giant, until it runs out of helium, too.

      White Dwarf/Planetary Nebulae: The outer layers continue to escape into space to form a planetary nebula, while the star at the centre starts to collapse to form the cooler white dwarf <— THE BEST BIT! 😉 😀

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