Download Goal: To understand the post main sequence evolutions of

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
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?
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
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”
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
Eta Car
• LBV
• 100-150 solar masses
• 2.5k parsecs from earth
(100X further than Sirius)
10k to 20k years to live
http://etacar.umn.edu/etainfo/history/
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.
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
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.
Oddities
• Emission lines
• Lines which don’t quite match up with
Hydrogen
Solution
• You are looking at the gas ejected from the
star
• Not seeing the star
• The lines are all shifted
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…
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.
So why study stars so rare?
• What influence could they possibly have?
• Well, it turns out the rarest stars have the
greatest impacts
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
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
Dust
• In addition these massive stars seem to
create a majority of the dust in our galaxy
• This helps in the formation of planets.
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
Conclusion
•
•
•
•
Massive stars are powerful
Destructive
Almost unpredictable
But alter the future of the galaxy