4.8.1.2 - life cycle of a star

WHta is the life cycle of a star determined by?

the size of the star

list of a small stars (like our suns) life cycle

• nebula

• protostar

• main sequence star

• red giant

• white dwarf

• black dwarf

list a large stars life cycle.

• nebula

• protostar

• main sequence star

• red super giant

• supernova

• neutron star or black hole

Describe the cycle up to main sequence star.

Stars initially form from a cloud of dust and gas - called nebula

The force of gravity pulls the dust and gas together to form a PROTOSTAR

The temperature rises as the star gets denser and more particles collide with each other. When the temp gets high enough, hydrogen nuclei undergo nuclear fusion to form helium nuclei. This gives out huge amounts of engird which keeps the core of the star very hot

Star now enters a long stable period where the outward pressure caused nu clear fusion reactions that try to expand the star balmavce the force of gravity pulling eveythytung together . So the fusion reactions lead to an equilibrium between he gravitational collapse of a star and the expansion of a star due to fusion energy .

This is called a main sequence star and typically lasts several billion years

hw long does main sequence star last?

several billions of years

what charcertieses a main sequence star?

In a main sequence star the fusion reactions lead to an equilibrium between he gravitational collapse of a star and the expansion of a star due to fusion energy .

Describe the red giant / red super giant phase

Eventually hydrogen begins to run out and the star swells into a RED GIANT. Or if large a RED SUPER GIANT. Becomes red as the surface cools. Fusions of helium and other elements occur (fusion processes in stars produce all the naturally occurring elements ) Heavier elements up to iron are created in the core of a star

end of a life cycle for a small star?

The star becomes unstable and ejects an outer layer of dust and gas. This leaves behind a hot, dense solid core - a WHITE DWARF

As the white dward cools down it emits less enter. When it no longer emits a significant amount of energy - it is called a black dwarf

end of a large stars life cycle

Big stars undergo more fusion and expand and contract several times, forming elements as heavy as iron in various nuclear reactions. Eventually they’ll explode into s supernova - forming elements heavier than iron and ejecting them into the universe to form mew planets and stars

Supernova (the explosion of a massive star) distributes the elements through the universe

Exploding supernova throws the outer layer of dust and gas into space - leaving a very dense core called a neutron star. If the star is massive enough it becomes a black hole (super dense point where not even lifght can escape)

what do supernovas do?

Supernova (the explosion of a massive star) distributes the elements through the universe

what is supernova?

the explosion of a massive star