What is a nebula?

A nebula is a large cloud of dust and gas.

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What happens when a nebula becomes very large?

Gravity pulls the particles of dust and gas together to form a protostar. 

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What happens when a protostar becomes very large?

Gravity becomes stronger, which pulls the particles closer together and increases the temperature and pressure.


At some point nuclear fusion will start fusing hydrogen nuclei together. 

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What do we call a protostar once nuclear fusion starts?

A main sequence star.

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Which two forces are in balance in a main sequence star?

The energy released from nuclear fusion creates an outward force that balances against the inward force from gravity.

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Which elements undergo nuclear fusion in a main sequence star?

Hydrogen nuclei fuse to make helium nuclei. 

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How long does a main sequence star last?

Until all of the hydrogen is used up.


This could be millions or billions of years.

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What two things could a main sequence star become once it runs out of hydrogen?


What determines which it becomes?

If it is relatively small, it will become a red giant.


If it is relatively large, it will become a red super giant. 

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For a red giant, what are the final phases of the star's lifecycle?

The red giant will become a white dwarf, which will then become a black dwarf as it cools.  

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Which elements can be formed in the red giant or red super giant phase?

Elements heavier than helium, up to iron on the periodic table. 

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For a red super giant, what happens next in the star's lifecycle?

It will explode in a supernova. 

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Which elements can be formed in a supernova?

Supernovas form elements heavier than iron, which are fired across the universe as they explode.

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What two things could form after a supernova?


What determines which is formed?

If the star was large, it would condense to form a neutron star.


If it was very large, it would collapse to form a black hole.  

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What is a neutron star?

An extremely dense mass of neutrons. 

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What is a black hole?

A black hole is a region where gravity is so strong that nothing can escape.


This means no particles, or even electromagnetic radiation such as light, can escape.

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