1. Evolution of the Solar System

2. Nebula
A cloud of dust and gas attracted together by gravity

3. Birth of the Sun
Nuclear fusion reactions take place at centre – hydrogen nuclei are fused together to make helium, releasing enormous amounts of energy

4. Planetary formation
Inner planets made from more dense material (Rocky), outer planets are mainly gas (Gas Giants)

6. Stable stars Stars are stable because the inward forces of gravity
are balanced by the outward force of radiation

7. Future of the Solar System – Sun becomes a Red Giant star
Hydrogen fuel in core runs out
Outward radiation pressure falls, so forces of gravity mean that centre of star collapses
Rapid burning of remaining hydrogen
Pressure and temperature now high enough in the core to fuse helium
Sun expands out to the orbit of Earth, swallowing up the inner planets
Cooler surface temperature – red colour

8. White Dwarf star
Helium and hydrogen fuel in core is used up. Fusion ceases.
The outer layers of star are “puffed away” into space
The remaining centre of the star cools and gets smaller

9. Black Dwarf star Eventually star cools and fades
This is the end of a life which has taken 10 billion years

10. What happens to stars much larger than the Sun?
Stars that are >8 x mass of Sun will have much shorter lives, and burn much hotter
A star 25 x mass of Sun gets through its life 1000 times faster
After a time fusing hydrogen (‘main sequence’), these larger stars start fusing heavier and heavier elements in shells (like an onion) with the heaviest elements at the core
The star becomes a Red Giant or Red Supergiant

11. Core of star

12. What happens after the Red Giant/Supergiant phase?
Fusion of iron doesn’t release any net energy, so fusion stops at the centre of the core
The star collapses
A massive amount of energy is released
This is a supernova explosion

13. A Supernova
The enormous gravitational pressure compresses the core to a million million kilograms per cubic metre and raises its temperature to 10,000 million degrees Celsius
The core collapses in 1/10 second from 12,000 km in diameter to 20 km – forming a neutron star
The outer layer collapse in and rebound off the core releasing enormous amounts of energy in a Type II supernova explosion

14. Heavier elements (above iron) are formed in the supernova explosion
For a few weeks the supernova is brighter than a whole galaxy
For very large stars it is possible for the neutron core to collapse to become a black hole
If not, the star, which is spinning, can be detected as a pulsar

15. SN 1987A – before and after
SN 1987A – before and after

16. M1
Supernova
explosion
remnant
from 1054 AD

17. Crab nebula pulsar
Imaged by Chandra X-ray telescope

18. Black Holes and Pulsars
Black Holes are caused when the concentration of mass is so large that the light itself can’t escape the pull of gravity. They can’t be observed directly but by their gravitational effect on other bodies. Material being sucked into a black hole gets accelerated to such high speeds that X-rays are emitted.
Pulsars are rotating neutron stars that emit short bursts of radiation at very regular intervals. The radiation pulses are caused by the rotating magnetic field.

19. Pulsar

20. Black Holes
Companion star
X-rays
Black hole
Accretion disk

21. Neutron star Very dense star formed
Some of these have strong magnetic field, which generate radiowaves
As they spin they give off pulses of radiowaves – called pulsars

22. Black hole
Very massive stars will end up as black holes where gravity is so strong that even light can’t escape