1. Stellar Evolution
Lab 5

2. What is a Star?
The basic difference between a star and a planet is that
a star emits light produced in its interior by nuclear 'burning‘
a planet only shines by reflected light

3. The Hertsprung-Russell Diagram
In 1912, Danish astronomer Ejnar Hertzsprung and American astronomer Henry Russell independently graphed the luminosity vs. temperatures for thousands of stars and found a surprising relationship
The Hertzsprung-Russel (H-R) diagram shows the evolution of stars based on their characteristics of surface temperature, luminosity and mass

4. H-R Diagram and Main Sequence Stars
The H-R Diagram shows that most of the stars lie along a smooth diagonal curve called the main sequence where
Hot, luminous stars appear on the upper left
Cool, dim stars in the lower right
~90% of the stars fall on the main sequence

6. Off Main Sequence Stars
Off the main sequence, there are
cool, bright stars in the upper right
hot, dim stars in the lower left

7. Main Sequence Stars A large number of stars are
chemically homogeneous
burn hydrogen to helium in their cores
emit luminosity ~ inversely proportional to the 4th power of their Temp
emit luminosity ~ directly proportional to the 4th power of their mass
These stars are called main-sequence stars

8. Luminosity vs radius
the radius of the stars increases as proceed bottom left diagonally to top right:
Sirius B = 0.01 solar radius
Sun = 1 solar radius
Spica = 10 solar radii
Rigel = 100 solar radii
Betelgeuse = 1000 solar radii

9. Mass vs luminosity
stars along the main sequence vary from the highest (~30 solar masses) at the top left to the lowest (~ 0.1 solar mass) at the bottom right
our Sun is an average star

10. Classes of Stars by Luminosity
The H-R diagram summarizes the types of stars in the universe:
Class Description Familiar Examples
Ia Bright Supergiants Rigel, Betelgeuse
Ib Supergiants Polaris (the North star), Antares
II Bright Giants Mintaka (delta Orionis)
III Giants Arcturus, Capella
IV Sub-giants Altair, Achenrar
V Main sequence Sun, Sirius
not classified White dwarfs Sirius B, Procyon B
White dwarfs stars are not classified because their stellar spectra are different from most other stars

11. Life on the Main Sequence
Stars on the main sequence burn by fusing H into He
Large stars tend to have higher core temperatures than smaller stars, so they burn the hydrogen fuel in the core quickly and have shorter lifetimes

12. HYDROGEN!!!!!! Small stars burn H more slowly.
The length of time a star spends on the main sequence depends upon how quickly the hydrogen gets used up
Once the hydrogen in the core is gone the mass of the star determines what happens next
The Sun is ~ halfway through its life of 10 billion years

13. Limits Shown on H-R
H-R shows a definite upper limit for Main Sequence stars, all stars more massive than this will have ended their hydrogen burning existence already.
Maximum mass for a Main Sequence is ~ 60 times the Solar Mass
Minimum mass of a star is ~ 0.1 of a Solar Mass, the mass required to produce nuclear reactions in the core.
The surface temperature of stars varies from 2000 to 35,000 degrees
Smaller stars are much more numerous than other types of stars.

15. Explanation

16. Another Version of the H-R

17. Yet Another Version

18. Interrelationships