AQA GCSE Life cycle of a star - Science Worksheets

AQA GCSE Life cycle of a star(Physics)

Life cycle of a Star

Birth of a star

Stars, including our Sun are formed from a nebula.

A nebula is a cloud of gas and dust. It mostly gas, with some dust.

Nebula shown in the image below:

The gas and dust particles in the nebula have mass, so there is gravitational attraction between the particles. As a result gravity pulls the gas and dust together, causing the material to clump and form a denser region called a protostar.

Protostar shown in the image below:

As the protostar gets denser, the temperature increases. When it gets hot and dense enough, nuclear fusion starts in the core.

Once fusion of hydrogen into helium begins, a new main-sequence star is born. This process releases huge amounts of energy and light.

A main Sequence star is shown below.

Maintaining stable size of a main sequence stars

Our Sun is a main sequence star and it maintains a relatively stable size.

Due to nuclear fusion of hydrogen to helium, there is an outward force of radiation from the core of the star.

However, as the star has a mass, there is an inward force of gravity that tries to pull the star inward.

Stars in main sequence will remain a relatively stable size because the outward force of radiation is balanced by the inward force of gravity.

This does assume that nuclear fusion continues to provide the outward force of radiation. At the end of the main sequence stage the hydrogen nuclei runs out, so outward force of radiation decreases.

Due to inward force of gravity the core of the star collapses, causing the core to heat up. This causes the outer layers to swell leading to the formation of a red giant or red supergiant

Red giant or Red super giant.

Stars that are of a similar mass to our Sun will form a red giant after their main sequence has finished.

Stars that have a mass much greater than our Sun will form a red supergiant once their main sequence has finished.

Stars of a similar mass to our Sun	Stars that have a mass much greater than our Sun
Once hydrogen is used up, main sequence stage ends, core collapses, outer layers swell to form a red giant	Once hydrogen i used up, main sequence stage ends, core collapses, outer layers swell to form a red supergiant
The helium will be fused to form other light elements. No elements will be formed that has an atomic mass greater than that of iron. This is because up to iron energy is released during the fusion process, beyond iron energy is needed overall for the fusion process.	The red supergiant will collapse inwards, causing huge amounts of compression. This allows for the fusion of nuclei to form nuclei heavier than iron such as uranium.
Once all of the light elements have been fused, all the fusion stops, so there is no longer any outward force due to radatiation. The inward force of gravity causes the star to collapse in on itself, heating up to form a white dwarf	Suddenly, this compression is reversed in an explosion called a supernova.
Over time the white dwarf will then cool to form a black dwarf.	The supernova will distribute these heavy nuclei. This is why we have uranium on Earth, its due to a previous supernova.
	During the supernova, the core of the star is compressed, and the outer layers are flung off. The core is compressed into either a neutron star, or if a very massive star was present then a black hole is formed.