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The sun and other stars


Pressure, volume and temperature

As the temperature increases, the particles have more energy and move faster. This increases their momentum and makes them collide with the sides of the container with more force.

If the volume is kept constant, the effect of doubling the temperature will be to double the pressure.

If the container is allowed to expand at constant pressure, the effect of doubling the temperature will be to double the volume.

Both these changes work in reverse. For example, a gas can actually be heated up by compressing it.

These two gas laws can be represented using the following equations:

pressure/temperature = constant

volume/temperature = constant

When using these equations, the temperature must be in Kelvins.

Formation of a protostar

A star begins its life as a cloud of gas, which is mostly hydrogen and helium. The particles experience a very weak attraction towards each other due to gravity [gravity: The force of attraction between all objects. The more mass an object has, the larger the force of gravity it exerts..

As the gas cloud becomes denser, the effect of gravity is to increase the pressure [pressure: Force per unit area. and temperature. As more gas is drawn in by the increasing gravity, the mass of the cloud increases and therefore so does its gravity.

The increasing gravity compresses the gas further so that it becomes hotter and denser. It eventually becomes a protostar.

Stellar system formation

Stellar system formation

When the temperature and pressure become high enough, the hydrogen nuclei fuse into helium nuclei, releasing large amounts of energy. The star is now a stable main sequence star.


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