1. Stars on and off the Main Sequence
Just a history of a star’s birth, life and death

2. Main Sequence Stars Where are they on the H-R Diagram?
How long is their life compared to other stars?
What is their dying process?
What do they ultimately become?
Why?

3. A Look at the Non-Main Sequence Stars: Birth and Death of Stars
Protostars
T-Tauri stars
Brown Dwarfs
Red dwarfs
Neutron stars
White dwarfs
Red Giants
Super Giants

4. Protostars A protostar is what you have before a star forms
If it has enough mass and begins to fuse, it becomes a T-Tauri star
If it does not have enough mass it becomes a Brown Dwarf (not red)

5. T-Tauri Stars
Star's formation and evolution right before it becomes a main sequence star
Occurs at the end of the protostar phase
Gravitational pressure holding the star together is the source of all its energy

6. T-Tauri Stars Continued
Don't have enough pressure and temperature at their cores to generate nuclear fusion
Same temperature as MS stars but brighter because they're a larger

7. T-Tauri Stars Have large areas of sunspot coverage
Have intense X-ray flares
Extremely powerful stellar winds
Remain in the T Tauri stage for about 100 million years

8. Main Sequence Stars, Again
The majority of all stars are main sequence stars
Our nearest neighbors, Proxima Centauri, Sirius and Alpha Centauri are main sequence stars
Stars can vary in size, mass and brightness

9. Main Sequence Continued
All doing the same thing
Converting hydrogen into helium in their cores
Releasing a tremendous amount of energy

10. Main Sequence Continued
In a state of hydrostatic equilibrium
Gravity is pulling the star inward
Pressure from all the fusion reactions in the star are pushing outward

11. Main Sequence Continued
Lower mass limit for a main sequence star is about 0.08 times the mass of the Sun (ex: Red Dwarf)
To more than 100 times the mass of the Sun

12. Red Giant Star
When an average star like our Sun consumes all hydrogen in its’ core, fusion stops
No longer generates outward pressure to counteract inward pressure
Outer shell of H around core ignites, prolonging life of star

13. Red Giants Continued
But the shell of ignited H causes it to increase in size dramatically
Can be 100 times larger than it was in its main sequence phase

14. Red Giants Continued
When hydrogen fuel is used up, further shells of helium and heavier elements can be consumed in fusion reactions
Will only last a few hundred million years before it runs out of fuel completely and becomes a white dwarf.

15. White Dwarf Stars
An average star has completely run out of hydrogen fuel in its core
It lacks the mass to force higher elements into fusion reaction
It becomes a white dwarf star

16. White Dwarf Stars Continued
Outward light pressure from the fusion reaction stops
Star collapses inward under its own gravity
No fusion reactions happening and cools down
Process takes hundreds of billions of years

17. Red Dwarf Stars Most common kind of MS stars Low mass
Much cooler than stars like our Sun
Able to keep the hydrogen fuel mixing into their core for a longer time

18. Red Dwarf Stars Continued
Can conserve their fuel for much longer than other stars
Some red dwarf stars will burn for up to 10 trillion years
The smallest red dwarfs are times the mass of the Sun and largest up to ½ our Sun

19. Neutron Stars
If a stars has between 1.35 and 2.1 times the mass of the Sun the star dies in a catastrophic supernova explosion
The remaining core becomes a neutron star

20. Neutron Stars Continued
It is an exotic type of star that is composed entirely of neutrons
How? The intense gravity of the neutron star crushes protons and electrons together to form neutrons

21. Neutron Stars Continued
More massive stars do not become neutron stars
What do they become?
What do we know about these structures created by the death of super massive stars?

22. Supergiant Stars
The largest stars in the Universe are supergiant stars
Dozens of times the mass of the Sun
Consuming hydrogen fuel at an enormous rate

23. Supergiant Stars Continued
Will consume all the fuel in their cores within just a few million years
Live fast and die young
Detonating as supernovae
Disintegrating themselves in the process
Betelgeuse is a prominent example of a red supergiant star. It is located at the shoulder of Orion

24. Nova and Other Things to Consider
Nova means "new star"
They are actually "newly visible" stars
One model of novae suggests that they occur in binary systems

25. Nova Continued One is a white dwarf
The other is on its way to becoming a red giant
The red giant can lose mass which would trigger hydrogen fusion as it falls on the white dwarf

26. Nova Continued
This would blow the gas off and the process could repeat itself. A notable nova example is Nova Cygni 1975.

27. Pulsars Evidence: precisely repeated radio pulses
Attributed to rotating neutron stars which emit lighthouse type sweeping beams as they rotate

28. Pulsars Continued
Variations in the normal periodic rate are interpreted as energy loss mechanisms or, in one case, taken as evidence of planets around the pulsar

29. Quasars These objects were named Quasistellar Radio Sources
Quasars are closely related to the active galaxies
The quasars have very large redshifts

30. Quasars Continued
Quasars are extremely luminous at all wavelengths and exhibit variability on timescales as little as hours, indicating that their enormous energy output originates in a very compact source

31. Black Holes What are they? How do they form?
What do we know about them?
What don’t we know?
How does time operate at a black hole? How does time operate inside the black hole?

32. Black Holes Continued What is singularity? What is the event horizon?
Do black holes rotate?
What are the only emissions from a black hole?

34. We will add more to the Hertzsprung-Russell Diagram
As we look at more information
As we look at mass
As we look at cycles
As we look at nebulae