1. Goal: To understand the post main sequence evolutions of the most massive stars Objectives: 1)To learn about Eta Carinae and LBVs 2)To learn about what Wolf-Rayet stars are 3)To understand the effects these stars have on their surroundings and why they are important for the evolution of the galaxy 4) To explore a little bit more in depth as to what happens when these stars die

2. Massive Stars Are rare, but special A 100 solar mass star only lives for about a million years Luckily that makes these massive stars very easy to find Where do you think we will have to find them?

3. Luminous Blue Variable stars (LBV) The first stage of post main sequence evolution for all stars > 25 solar masses. While on main sequence these stars are 10,000 to 1 million times brighter than our sun So, the Hydrostatic Equilibrium for the outer part of the star barely holds

4. Mass loss Needless to say they loose mass very fast to stellar winds About an EARTH mass to 100 Earth masses per YEAR. A solar mass in about a thousand to 100,000 years. The largest of these stars can loose a solar mass in a single “burp”

5. Eta Car “Eta Carinae (Eta) is one of the most remarkable of all well-studied stars and perhaps the most poorly understood. Observations with the Hubble Space Telescope and other modern instruments have solved a few of the mysteries concerning this object while opening a comparable number of new ones.” Kris Davidson and Roberta Humphries, U. Minnesota

6. Eta Car LBV 100-150 solar masses 2.5k parsecs from earth (100X further than Sirius) 10k to 20k years to live

7. http://etacar.umn.edu/etainfo/history/

8. Eddington Limit There is a limit to the brightness of a star If a star is too bright the radiation pressure at the surface pushes plasma out MORE than gravity pulls in Gravity looses… For 20 years Eta Car seems to have exceeded this limit by a factor of 4.

9. So what are we seeing here? The loss of light is due to a massive ejection of material which then forms dust As much as 1 solar mass may have been burped out in this one even dubbed the “Great Eruption” Supernova impostor Keep in mind… Not looking at the star necessarily but often times the gas AROUND the star sometimes the gas thrown off of the star

12. Next stage: Wolf-Rayet star Eventually the LBV will throw all of its outer layers off. No more H This leaves a Wolf-Rayet star. However, it also is throwing off lots of material.

14. Oddities Emission lines Lines which don’t quite match up with Hydrogen

15. Solution You are looking at the gas ejected from the star Not seeing the star The lines are all shifted

16. Doppler shift The gas is moving at us at hundreds to thousands of km per second This causes the lines to be “blue shifted” as the emitted wavelengths are compressed. A bit of explanation coming here…

17. Even Wolf-Rayet stars evolve These stars are so massive and do things so fast they evolve. They go from having poor Hydrogen lines and Nitrogen to no H and Carbon. This occurs as the layers get tossed off and the core continues to fuse heavier elements.

18. So why study stars so rare? What influence could they possibly have? Well, it turns out the rarest stars have the greatest impacts

19. Super bubbles The material they throw out is usually pretty hot (especially when they supernova at the end of their lives) This creates a giant bubble of hot gas Often you will get a few in the same small region also (they exist in clusters after all) whose bubble all combine to form a super bubble

20. Super bubble bursts If the bubble gets 1k parsecs in size it can break through the plane of the galaxy When this happens the metal rich gas gets thrown very far and spreads to a very large region of the galaxy So, these massive stars not only throw out large amounts of metals but spread them throughout the galaxy

21. Dust In addition these massive stars seem to create a majority of the dust in our galaxy This helps in the formation of planets.

22. Deaths Their deaths are thought to be spectacular. None witnessed though, they are that rare. Hypernova – a super strengthed super nova Gamma Ray burst – this one takes a bit of explaining

23. Conclusion Massive stars are powerful Destructive Almost unpredictable But alter the future of the galaxy