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Goal: To understand the post main sequence evolutions of the most massive stars

Goal: To understand the post main sequence evolutions of the most massive stars. Objectives: To learn about Eta Carinae and LBVs To learn about what Wolf-Rayet stars are To understand the effects these stars have on their surroundings and why they are important for the evolution of the galaxy

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Goal: To understand the post main sequence evolutions of the most massive stars

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  1. Goal: To understand the post main sequence evolutions of the most massive stars Objectives: To learn about Eta Carinae and LBVs To learn about what Wolf-Rayet stars are 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

  10. 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.

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

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

  13. 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…

  14. 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.

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

  16. 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

  17. 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

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

  19. 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

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

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