Download (Star Stuff) ( 11-9-10)

Chapter 12. Star Stuff (mostly different from book)
I.
Birth of Stars from Interstellar Clouds
•Young stars near clouds of gas and dust
•Contraction and heating of clouds into protostars
• Hydrogen fusion stops collapse
II. Leaving the Main Sequence: Hydrogen fusion stops
1. Low mass stars (M < 0.4 solar masses)
Not enough mass to ever fuse any element heavier than
Hydrogen → white dwarf
2.Intermediate mass stars (0.4 solar masses < M < 4 solar masses,
including our Sun)
He fusion, red giant, ejects outer layers → white dwarf
3.High mass Stars (M > 4 solar masses)
Fusion of He,C,O,…..but not Fe (Iron) fusion
Faster and faster → Core collapses → Supernova
blows up and produces all elements heavier than Fe
How massive are newborn stars?
A cluster of many stars can form out of a single cloud.
Luminosity
•Very
massive
stars are
rare
•Low-mass
stars are
common.
Temperature
•Minimum
mass
needed to
become a
star: 0.08
solar masses
• How massive are newborn stars?
 Low mass stars are more numerous than high mass
stars
 Newborn stars come in a range of masses, but cannot
be less massive than 0.08MSun.
 Below this mass, pressure in the core is not enough
(10 million K) for hydrogen fusion, and the object
becomes a “failed star” known as a brown dwarf.
Equilibrium inside M.S. stars
Question
What happens when a star can no longer fuse
hydrogen to helium in its core?
A.
B.
C.
D.
Core cools off
Core shrinks and heats up
Core stays at same temperature
Helium fusion immediately begins
Question
What happens when a star can no longer fuse
hydrogen to helium in its core?
A.
B.
C.
D.
Core cools off
Core shrinks and heats up
Core stays at same temperature
Helium fusion immediately begins
Ch. 12 Part II (not like book). Leaving the Main
Sequence: Hydrogen fusion stops
1. Low mass stars (M < 0.4 solar masses)
Not enough mass to ever fuse any element heavier than
Hydrogen  white dwarf
2.Intermediate mass stars (0.4 solar masses
< M < 4 solar masses, including our Sun)
He fusion, red giant, ejects outer layers  white dwarf
3.High mass Stars (M > 4 solar masses)
Fusion of He,C,O,…..but not Fe (Iron) fusion
Faster and faster  Core collapses  Supernova
 Blows up and produces all elements heavier than Fe
Outline of Chapter 12 Part II Evolution
and Death of Stars
I.
Leaving the Main Sequence:
BEWARE THAT THE BOOK DOES NOT USE THE
SAME DEFINITIONS OF LOW, INTERMEDIATE
AND HIGH MASS STARS.
AS MENTIONED, THE EXAM WILL BE BASED ON THE
LECTURES AND NOT ON THE BOOK
Remember: Stellar Masses
Composition inside M.S. stars
Eventually
the core
fills up with
helium and
hydrogen
fusion stops
Leaving the Main Sequence:
Hydrogen fusion stops
1. Low mass stars (M < 0.4 solar masses)
Not enough mass to ever fuse any element heavier than
Hydrogen  white dwarf
White Dwarfs
I. Leaving the Main Sequence:
Hydrogen fusion stops
2. Intermediate mass stars (0.4 solar
masses < M < 4 solar masses, including
our Sun)
He fusion, red giant, ejects outer layers  white
dwarf
Helium fusion requires much higher temperatures than
hydrogen fusion because larger charge leads to greater
repulsion
Stars like our Sun become Red Giants after they
leave the M.S. and eventually White Dwarfs
Most red giants stars eject their outer layers
A star like our
sun dies by
puffing off its
outer layers,
creating a
planetary
nebula.
Only a white
dwarf is left
behind
A star like our
sun dies by
puffing off its
outer layers,
creating a
planetary
nebula.
Only a white
dwarf is left
behind
A star like our
sun dies by
puffing off its
outer layers,
creating a
planetary
nebula.
Only a white
dwarf is left
behind
A star like our
sun dies by
puffing off its
outer layers,
creating a
planetary
nebula.
Only a white
dwarf is left
behind
II. Leaving the Main Sequence:
Hydrogen fusion stops
3.High mass Stars (M > 4 solar masses)
Fusion of He,C,O,…..but not Fe (Iron) fusion
Faster and faster  Core collapses  Supernova
 Produces all elements heavier than Fe and blows up
•
•
Supernovas
3. High mass star (M > 4 solar masses)
•Fusion of He,C,O,…..but not Fe (Iron) fusion
Faster and faster  Core collapses  Supernova
Produces all elements heavier than Fe and blows
envelope apart ejecting to interstellar space most of its
mass
• Supernova Remnants:
Crab nebula and others
An evolved massive star (M > 4 Msun)
An evolved massive star (M > 4 Msun)
before
after
Supernova 1987A in a nearby galaxy is the nearest supernova
observed in the last 400 years
Crab Nebula: Remnant of a supernova observed in 1054 A.D.
Pulsar (a kind
if neutron
star) at center
of Crab
nebula
Older Supernova Remnant