1. STARS

2. Stars A star is usually a large ball of gas held together by gravity
Stars produce tremendous amounts of energy that shine

3. Stars Some stars are very old and do not emit any radiation
Some stars can be as big as a planet

4. Energy Production
Stars use Nuclear fusion in their cores to produce most of their energy

5. Nuclear Fusion
The combining of nuclei of smaller elements to form the nuclei of larger elements with some mass being converted to energy
This process can only occur in extremely high temperatures and pressures

6. Nuclear Fusion Example
Our sun converts hydrogen nuclei to helium nuclei with about 0.07 % of the mass being converted to energy

7. Luminosity and Temp. Diagram (PAGE 15, ESRT)
Luminosity is a measure of how bright a star is in relation to the sun if the stars were all the same distance from the observer

8. Apparent Brightness
What we really see in a star is dependent upon the stars absolute luminosity and distance away from us

10. Star Types

11. Main Sequence Make up about 90% of all studied stars
Most stars spend a majority of their life as a main sequence star
As main sequence stars temperature increases, their luminosity also increases.
These stars can range form blue to red in color (ESRT)

13. Giants Red, Orange, and Yellow in color
Easily visible because of their luminosity and how big they are (10 times or more the diameter of the sun)
Low temperatures because of how late they are in their evolution

15. Can be anywhere from 100 to 1000 times the diameter of the sun
Super Giants
Can be anywhere from 100 to 1000 times the diameter of the sun
High luminosity representing the late evolution of the star. Super giants usually explode in a tremendous event called a supernova

17. Not all white dwarfs are white in color
About the size of Earth
Not all white dwarfs are white in color
Hot on the surface

19. Black Dwarfs
When a white dwarf cools and no longer emits much electromagnetic energy it becomes “dead”

21. Star Origin and Evolution

22. Origin
Gravity causes gas and dust clouds to clump up, forming larger and larger balls of gas and dust

23. Origin
When the gas and dust start to become big enough (around the size of Jupiter) they have enough gravitational contraction and the result is the beginning of nuclear fusion.
Nuclear fusion gives the star enough electromagnetic energy to begin shining and a star is born

24. Evolution
Evolution of a star after they spend most of their lives as a main sequence star depends mostly on the original mass

25. Main sequence stars expand to become red giants or supergiants.
Evolution
Main sequence stars expand to become red giants or supergiants.

26. Evolution
Stars with a mass 1.5 times greater than the sun form into supergiants, then rapidly collapse forming a body much smaller than a white dwarf
A high mass will form a neutron star
An extremely high mass will have a density so high it creates an extreme gravity field, where nothing can escape.
This is known as a black hole

27. Evolution
Stars with a mass less than 1.5 times the sun will form into a white dwarf. They use up most of their nuclear fuel while becoming a white dwarf and eventually die to become a black dwarf