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ANNOUNCEMENTS 11/09/11
 C.L.U.E. Thursday evening 11/10/11
 There WILL be a question about massive star
evolution, and we will answer it today in lecture.
 Survey still open for your indicating the topics
you are most unsure of for Monday’s exam 3.
 You do have a textbook, and for most of your
uncertainties with the various topics, reading the
text will help!
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Short visual review of evolution - sun-like star
Death sequence of the Sun
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Understanding stages of
low-mass star death
Radius of the star turning into a
red giant is increasing due to the
great increase in luminosity being
provided by the fusion occurring
in a shell around the core.
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Evolution of Stars
Part II – MASSIVE STARS
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Learning Goals:
 Explain why the much higher mass of some
stars causes their evolution to be so different from
the Sun.
Outline the basic stages of the evolution of a
massive star
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Closer look at
stars in Orion:
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Betelgeuse
~20 x solar mass
Can actually SEE
this star’s surface!
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How bright will Betelgeuse be when it goes
supernova?
m  M  5log( d)  5
m  M  5log( d)  5


msn  15  log 10.005  5
msn  15  log( 200)  5
msn  17
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m fullmoon  13

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100+ times
as massive
as the Sun.
Eta Carinae
It is so
massive that
it can barely
hold itself
together.
Some
astronomers
think Eta
Carinae
might die in
a supernova
blast within
our lifetime.
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http://www.spitzer.caltech.edu/Media/releases/ssc2005-12/ssc2005-12a.shtml
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Some perspective
CNO cycle
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Evolution for a star > 10 times Sun’s mass
 No helium flash.
 Helium  carbon fusion starts when
temperature gets high enough
(~100,000,000 K)
 Core does NOT become degenerate
 Rest of star expands
Triple-alpha fusion of He to
C needs extremely high T’s
to operate.
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 Core shrinks, heats
 Carbon  oxygen fusion starts when temperature high enough
 Fusion continues to heavier and heavier nuclei
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Changes in temperature and luminosity for massive stars
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Mass > 10 solar masses
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Fusion to iron marks certain doom
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What happens to the star?
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Summary of the evolution of a high-mass star
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 Explain why the much higher mass of some
stars causes their evolution to be so different from
the Sun.
Outline the basic stages of the evolution of a
massive star
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