1. A cloud of gas and dust collapses due to gravity.
As it shrinks it gets hotter and denser. Eventually the central part of the cloud becomes so hot and dense that Nuclear Fusion reactions begin. A star is born.

2. Let’s zoom in to see what is happening inside the star.

4. CORE
This is the power house of the star where the nuclear fusion reactions produce the energy which eventually reaches the surface of the star to make it shine.

5. The force of gravity is continually trying to collapse the star
The force of gravity is continually trying to collapse the star. So why doesn’t it shrink?

6. The force of gravity is continually trying to collapse the star
The force of gravity is continually trying to collapse the star. So why doesn’t it shrink?
The heat radiating from the core pushes outwards. This Radiation Pressure balances the force of gravity so the star remains stable………for a few billion years.

7. Fusion of Hydrogen to Helium begins in a shell around the core
Core: mostly Helium
Eventually the hydrogen fuel in the core begins to run out. With less energy being produced there is less radiation pressure.
Gravity starts to take over – causing the core to collapse.
The collapsing core gets hotter and this starts nuclear fusion reactions in a spherical shell around the core. Radiation pressure increases and overcomes gravity to push the outer layers of the star outwards. The star expands to become a Red Giant.
The Helium in the shrinking core becomes hot enough to fuse into Carbon. The energy released pushes the outer layers into space. When the Helium fuel is exhausted the core collapses to form a White Dwarf star.

8. This is what Astronomers call a ‘Planetary Nebula’ (since it looks a little like a planet through a telescope).
The White Dwarf at the centre gradually cools turning red, brown and eventually black – a Black Dwarf.
The Helium in the shrinking core becomes hot enough to fuse into Carbon. The energy released pushes the outer layers into space. When the Helium fuel is exhausted the core collapses to form a White Dwarf star.

9. A larger cloud of gas and dust collapses to form a larger, hotter star.

11. Towards the end of its life it expands to form a larger red giant called a Red Supergiant
The star remains stable for about 1 billion years. Nuclear Fusion proceeds at a furious rate to balance the large force of gravity.

13. In the core of the Supergiant star Helium undergoes nuclear fusion to make Carbon. Carbon then fuses to make Oxygen. Heavier and heavier elements are created until Iron. Iron cannot be fused so the reactions suddenly….. STOP.
With no radiation pressure to balance gravity the star collapses and bounces off the core in a huge explosion called a Supernova.

14. In the core of the Supergiant star Helium undergoes nuclear fusion to make Carbon. Carbon then fuses to make Oxygen. Heavier and heavier elements are created until Iron. Iron cannot be fused so the reactions suddenly….. STOP.
With no radiation pressure to balance gravity the star collapses and bounces off the core in a huge explosion called a Supernova.
There is enough energy in the explosion to create the nuclei of all the elements heavier than iron. These are thrown out into space ready to make the next generation of stars.

16. One of 2 strange objects remain……
A superdense neutron star or
A black hole

17. Large cloud of gas & dust
Stable star (Like the Sun)
Red Giant
White Dwarf
At the centre of a ‘Planetary Nebula’
Black hole or
Neutron star
Large cloud of gas & dust
Stable star (larger & hotter than the Sun)
Red Supergiant
Supernova

18. FUSION
D Taylor 2004

19. 3He + 3He → 4He + 21H
2H + 1H → 3He
1H + 1H → 2H + e+

20. Large cloud of gas & dust
Stable star (Like the Sun)
Red Giant
White Dwarf
At the centre of a ‘Planetary Nebula’
Black hole or
Neutron star
Large cloud of gas & dust
Stable star (larger & hotter than the Sun)
Red Supergiant
Supernova