1. ‘The life-cycle of stars’
Stellar Evolution
‘The life-cycle of stars’

2. What is a star? LARGE GLOWING BALL OF GAS Composed of H and He
Fixed points of light in space
Undergo fusion in their cores
Generate heat and light
Give off tremendous radiation

3. Star Energy
Nuclear Fusion – a nuclear reaction in which to atoms are fused together…
New elements are created and energy is released.
This process is responsible for creating ALL elements found in the universe…
in other words, we are all made from star dust.

4. Star Energy (con’t) Hydrogen fusion Helium fusion H + H  He +
He + He  Be +
As the mass of elements increases, energy production increases
Energy
More Energy

5. Properties of Stars Color & Temperature Brightness Size & Mass
Apparent vs. Absolute
Size & Mass
Composition

6. Hertzsprung-Russel Diagram
A graph showing the surface temperature and absolute brightness of a group of stars
Used to compare several properties of stars and estimate their sizes and distances
Shows star color, size, temperature and brightness

7. H-R Diagram

8. Low mass
Protostar
High mass

9. Nebula A cloud of gas and dust
Gravity causes the cloud to collapse and condense
Temperatures begin to increase = Glows
Fusion begins at VERY high temps.
(Some of the extra gas and dust may form planets)

10. Protostar Gravity pulls a nebula’s dust and gas into a denser cloud
As a nebula heats up, it contracts
A contracting cloud of dust with enough mass to form a star

11. Main Sequence Stars Core reaches a temp of ~15 million K.
Hydrogen begins to fuse into Helium in the core.
~90% of stars lifetime is spent in the main sequence stage.
Classified based on temperature and luminosity

12. Giant Stars Core decreases in size as all (or most) H is consumed
He fusion is occurring – producing more energy
Diameter increases x10
Surface temp decreases as star expands

13. Super Giants Form from massive stars
A chain of reactions take place in the core producing He, C, O, Ne, Mg, Si, S, Ar, Ca, Ti, Cr, Fe
Highest temperature = Blue Super Giants
Usually explode in a tremendous event called a supernova

14. Planetary Nebula
Energy from star becomes to decrease; no more elements to fuse
Star begins to collapse
Dying star surrounded by gases

15. Nova/Super Nova
The core of a giant star produces too much energy in it’s core and causes the outside of the star to expand.
The outer layer of gasses are blown out to space (nova, or supernova), leaving behind a small, hot core…

18. White Dwarf
Stars decrease in size ~ same diameter as earth, mass stays the same
Mass of sun, size of Earth
DENSITY INCREASES TREMENDOUSLY
Solid, but still hot, so it is glowing
Luminosity decreases

19. Neutron stars
Form from the remains of extremely massive stars after a supernova.
Very small ~ 30 km across
Density of 2 x 1014
Would be comparative to 1 sugar cube = mass of humanity

20. Black hole
If the core’s mass is even greater/denser than a neutron star, it collapses.
Surface gravity is so great that no matter can escape it…not even electromagnetic waves!

21. The fate of our Sun