1. Life-Cycle of Stars

2. Task
Using the information around the room, find out the life cycle of a star. Put all of this into order, from the beginning of a star, to the end.

3. Nebulae
Clouds of dust and gas

4. Protostar Hot gas heated through pressure Lasts about 10,000,000 years
Pre fusion

5. Main Sequence Star Hydrogen fusion begins and the star is born
Usually lasts 5 billion years or so
Stable due to balanced forces of gravity and pressure from fusion reactions

6. Red Giant Hydrogen fuel runs out
The core contracts due to gravity and the outer layers are shed
The star grows and cools into a red giant

7. White Dwarf
When the red giant has run out of all fuel and can fuse nothing more, it will lose its outer layers.
This leaves just the core, which is still extremely hot. It is so hot it glows white hot, hence the name “white dwarf”
Temp: 107 K interior but surface temps vary greatly (as low as 4000 K (about the same temp as a sun spot) to about K)

8. White dwarf stars eventually cool and become black dwarfs
… theoratically! None of these exist yet as the process takes longer than age of the universe to get to this stage. We are almost certain this WILL happen but it just HASN’T HAPPENED YET.

9. Useful diagram but note that it misses protostar phase.

10. Nebulae
Clouds of dust and gas

11. Protostar Hot gas heated through pressure Lasts about 10,000,000 years
Pre fusion

12. Massive Star
Stars much larger than our sun also have a main sequence phase but this tends to be shorter.
Many burn so hot that they become blue giants

13. Red Super Giant
Unlike a Red Giant, a Red Super Giant is large enough and hot enough to maintain fusion reactions with ever heavier elements up to iron.

14. Supernova
At the end of a Red Supergiant’s life it leaves layers of elements in the structure of the star like layers in an onion

15. Supernova
Fusion ends with Iron and with no outward radiation pressure the star begins to collapse under it’s own gravity

16. Supernova
The collapsing inner core is compressed into neutrons

17. Supernova
The outer layers then rebound off this neutron core in a shockwave (red ring)

18. Supernova
The rebound is then temporarily slowed by infalling material

19. Supernova
Before being re-activated by an as yet not fully understood process

20. Supernova
All this happens in just a few seconds and the supernova can shine as bright as an entire galaxy for a number of weeks

21. Supernova
Betelgeuse – highly unstable red supergiant about 600 ly away

22. Option A – Neutron Star
This is the fate of the cores of stars around 3x the mass of the Sun (or less)
Very dense (about the size of Earth but as heavy as the Sun)

23. Option B – Black Hole
When a star is more than 3x bigger that the sun, this leads to a black hole
The neutron core collapses further under extreme gravity
Nothing can escape a black hole, including light

24. Life Cycle of a Star Nebula
Clouds of gas and dust come together. Gravity pulls them together as a spinning ball of gas. This is getting so hot that it starts to glow.
Protostar
Gravity acting on the protostar makes it become smaller , hotter and shines brighter. This leads to fusion. This is when hydrogen atoms combine to form helium and releases energy.
It is gravity that holds the star together, and the build up of pressure from fusion that makes the star the size it is. As long as there is hydrogen there is energy being released.
Massive protostars burn faster than smaller protostars and don’t last as long
Red Giant (small stars only)
When hydrogen runs out, the core contracts due to gravity but the outer part expands and turns red. Which is a red giant. It will be so big, it will consume Mercury, Venus and Earth.
Red Supergiant (massive stars)
Similar to a red giant. The core contracts due to gravity and the pressure from fusion expands on a much bigger scale. The core collapses almost instantly causing it to explode (Supernova)
White Dwarf
Eventually, the core of the red giant remains, and will emit what ever energy is left
Black Dwarf
Eventually the white dwarf will no longer have any energy, and will become a black dwarf
Supernova
The remnants of the supernova gather with dust and gas in space. Gravity pulls this in and a new star is formed. Known as a second generation star.
Neutron Star
After the supernova, a very dense core is left. The neutron star. It could collapse into a black hole