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Big Bang, Black
Holes, No Math
ASTR/PHYS 109
Dr. David Toback
Lecture 22 & 23
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 1
Holes, No Math
Topic 2: Stars
Was due Today – L23
• Reading:
– (Unit 5)
• Pre-Lecture Reading Questions:
– Unit 5 Revision (if desired): Stage 1
• End-of-Chapter Quizzes:
– Chapter 15
• Papers:
– Paper 3 Revision (if desired): Stage 1 due
Wednesday
• Honors Papers:
– (Stage 2)
– Final paper due on the last day of class
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 2
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Topic 2: Stars
Unit 5: Big Objects
1. Galaxies
2. Star Birth and Death
3. More on Black Holes
It turns out that the way Galaxies
and Stars form is very similar…
start there
The way stars “die” depends on
the star itself… sometimes they
die to form a Black Hole
Today
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 3
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Topic 2: Stars
Important Buzz Words
Wanted to make sure we
explained some of the important
buzz words in astronomy:
– Red Giant
– Supernova
– White Dwarf
– Neutron Star
– Black Hole
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Topic 2: Stars
Today’s Lecture
• A star is born
• Nuclear reactions and gravity keep
stars alive and make them shine
• The life of stars: shining and
converting hydrogen into heavier
elements
• Life and death of stars like our Sun
• Life and death of massive stars
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Topic 2: Stars
Where are we now in the history?
A few hundred million years after
the bang, stars start forming
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Topic 2: Stars
Quick Summary of Galaxy Formation
• Half a million years after
the Big Bang we have lots
of neutral stuff floating
around in space
• Half a billion years after
the bang the stuff has
clumped into galaxies
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Topic 2: Stars
Stellar Clumps
• The galaxies start as giant spinning
areas of neutral, massive stuff kept
together by gravity
• Eventually, local areas that orbit around
the center of the galaxy are close
enough to each other that they also
start clumping due to gravity
• Eventually, the hydrogen and helium
atoms can start to interact with each
other
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Topic 2: Stars
Star Formation
• This is some
text..
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Topic 2: Stars
Step 2
• More…
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 10
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Topic 2: Stars
Step 3
• This is some text…
Beginnings
of planets!
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 11
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Topic 2: Stars
Stars have some things in
common with Spiral Galaxies
Will
be the
planets
Will
be the
star
Gee… kinda looks like Saturn also…
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Topic 2: Stars
Describing Stars
We tend to use metaphors to
describe Stars
1. Can think of them like people:
They have a birth, a life and
a death
2. Can think of them like a car:
They run on “fuel,” and “die”
when they run out of fuel
3. Can think of them like a
balloon: A giant collection of
atoms that are “forced” to
stay inside the balloon walls
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Topic 2: Stars
Proto-stars
•Gravity brings together the stuff
in a galaxy that has mass
•When the atoms (mostly
hydrogen and a little helium) get
close enough they start moving
quickly into the center
•However, need to get really
close before they will interact
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 14
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Topic 2: Stars
Low energy (temperature)
hydrogen reactions
Proton
Electro-magnitism Reaction
Same charges repel
Proton=Hydrogen
Proton
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Topic 2: Stars
A Star is Born
• When there are enough atoms, the large
amount of mass makes the pull to the center so
strong that the hydrogen starts moving quickly
into the center  become higher temperature
• When atoms reach a high enough temperature
(10 Million Kelvin) they start to have nuclear
interactions
Creates the light we see (makes stars
shine)
Atoms inside the Sun don’t move in the
same way the Earth orbits outside it
Call this a star
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Topic 2: Stars
Hydrogen Reactions at high
Temperatures
Proton
Proton + Proton
Deuterium + Electron + Neutrino
Anti-Electron
Nuclear
Reaction
Deuterium
Proton=Hydrogen
Neutrino
This is what we call Fusion
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get LOTS of energy
Holes, No MathOut-going particles
Topic 2: Stars
Proton
The Life and Death of Stars
A star’s life is effectively a
battle between:
1.Gravity trying to crush
everything into a tiny point
2.The nuclear interactions
“opposing” the gravity
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Topic 2: Stars
Only in the center of Stars
• The center of a
star is called the
core
• This is where the
particles have the
highest energy and
density  This is
where all the fusion
occurs
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 19
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Topic 2: Stars
Where does the energy come from?
• Mass of Deuterium is smaller
than the mass of two protons
• So what? E=mc2, so the
“mass energy” gets converted
into kinetic energy in the
collision
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Topic 2: Stars
Hydrogen Reactions
Proton
Proton + Proton
Deuterium + Electron + Neutrino
Anti-Electron
Nuclear
Reaction
Deuterium
Proton=Hydrogen
Neutrino
Fusion produces particles with LOTS of
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 21
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Topic 2: Stars
Proton
Hydrogen and Deuterium
Deuterium
Proton + Deuterium  3He + Photon
Again, lots of energy to the particles
Nuclear
Reaction
Photon
3He
Proton
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Topic 2: Stars
Creating Stable Helium
3He
3He
+ 3He  4He + 2 Hydrogens
More energy is released
Nuclear
Reaction
Hydrogen
4He
3He
Hydrogen
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Topic 2: Stars
Nuclear “Burning”
• In each nuclear reaction additional
energy is released
Some of the energy “turns into”
photons (and neutrinos)
– This is what makes stars shine
Some energy goes into the
increased speed of the atoms
– This is what keeps the star from
crushing itself
How?
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 24
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Topic 2: Stars
Thinking of a Star as a Balloon
• The hydrogen and
helium are the gas
inside the balloon,
the fusion speeds
them up so they
“try” to leave
• The gravity is what
keeps it all
together, like the
walls of the balloon
Gravity
holds it
together
Hydrogen and
Helium gas
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Topic 2: Stars
Small speed objects can’t leave the Earth
Look at the
different
things that
can happen
at various
speeds on
various size
“heavenly
bodies”
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Topic 2: Stars
Another example with the same speed
bullet but on the Moon
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Topic 2: Stars
If we move to an asteroid, then it
CAN leave
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Topic 2: Stars
Can build things that shoot fast
enough to leave the Moon
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 29
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Topic 2: Stars
Why doesn’t the Balloon deflate or pop?
If an atom has a
high speed or
there is only
small gravity
(star is small
mass) then the
atom will leave
the star
Small
Gravity
Hydrogen
and Helium
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 30
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Topic 2: Stars
Why doesn’t the Balloon deflate or pop?
• If gravity is strong (large
mass star), or the speed is
small then gravity drags
the atoms back to the
center
– Acts “like” the walls of a
balloon
– The more massive the
star the stronger the
walls
– Atoms don’t leave
Large
Gravity
Hydrogen
And Helium
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 31
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Topic 2: Stars
A Stable Star
• The nuclear reactions
speed up the atoms
– “Try to make the
balloon pop”
– Create light
• Gravity pulls it back
together
• The size of the balloon
depends on this balance
Gravity
Nuclear
Reactions
– Can stay stable for billions
of years
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 32
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Topic 2: Stars
The Fuel of a Star
The Hydrogen and Helium
provide the “fuel” that
both:
1. Creates the light we see
2. Keeps the star stable
Converts light atoms into
heavy
atoms
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes
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Topic 2: Stars
33
The Life of a Star
The star starts as a “ball” of
mostly hydrogen, with the fusion
in the core
What happens when it runs out of
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 34
fuel?
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Topic 2: Stars
What happens when the
Hydrogen Runs out?
• Without hydrogen fuel to make
things “expand,” gravity crushes
atoms closer and closer together
– It takes a temperature of 100
million Kelvin to fuse Helium, this
may not happen for many stars
• From there what happens next
depends on the “mass” of the star
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 35
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Topic 2: Stars
Start with Stars like our Sun
• Mid-sized stars (between 8% and 8
times the mass of our Sun) all typically
have a similar life
• Smaller than 8% of the Sun  won’t get
hot enough to fuse hydrogen
– Isn’t really a star at all
– Call this a brown dwarf
• More than 8 times the mass of our Sun
 complicated things can happen
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 36
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Topic 2: Stars
The Life and Death of our Sun
• Sun is using its hydrogen to create light
• Helium produced falls to the center
(the core)
• Today: Core only about 15 million
Kelvin  not hot enough to convert
Big Bang,helium
Black Massive
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Galaxies, Stars and Black Holes 37
into
Carbon
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Topic 2: Stars
Future: White Dwarf
When most of the hydrogen is used up,
the core gets crushed
Eventually the atoms get REALLY close to each
other and the strength of the repulsion
between the electrons from quantum mechanics
is so big that it balances out the gravity
Outer part becomes a Red Giant and then
diffuses into space
– Inner part stabilizes
• Call this a “White Dwarf”
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 38
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Topic 2: Stars
Lots of White Dwarfs in the Universe
• Hot core creates heavy elements
• Can shine for quite awhile
– This is why we call it “white”
• Really dense: An object with the
mass of the Sun shrunk to about
the size of the Earth
– This is why we call it a “dwarf”
• How dense? A pair of standard dice
would weigh about 5 tons
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 39
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Topic 2: Stars
White Dwarf  Black Dwarf
• Eventually a white dwarf star
runs out of the rest of its
fuel (nothing left but iron)
and it stops emitting light
• Call this a “Black Dwarf”
• However, predictions are that
it takes so long for this to
happen that none should
exist…
none
observed
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes
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Topic 2: Stars
40
Next move to
heavier stars…
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 41
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Topic 2: Stars
The Life of a Heavy Star
• For heavy stars the first part of their life is
the same as for lighter stars: after the
hydrogen runs out, gravity crushes the core
• What is different is that for heavy stars
there is so much mass that gravity can
continue to crush the core, and the
temperature can rise significantly
• For stars with more than 8 times the mass of
the Sun, the core can reach a temperature of
100 million Kelvin, and helium fusion can start
• Helium can fuse to make heavier elements
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 42
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Topic 2: Stars
Stages in a Massive Star’s Life
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 43
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Topic 2: Stars
Converting Helium to Beryllium
4He
4He
4
+ 4He4  8Beryllium
Nuclear
Reaction
8Beryllium
4He
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 44
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Topic 2: Stars
Converting Beryllium to Carbon
8Beryllium
8Beryllium
+ 4He 
Nuclear
Reaction
4He
12Carbon
+ Photon
12Carbon
Photon
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 45
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Topic 2: Stars
The Most Massive Stars
•For the heaviest
stars, after the
helium is used up can
start fusing Carbon
•Then Neon
•Keep going…Get
“shells” of the
various types of
atoms
•This is where the
atoms WE/Earth get
Bigcreated
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Galaxies, Stars and Black Holes 46
Topic 2: Stars
How Long do Stars Live?
Weird: stars with huge mass die
faster than lighter stars. Why?
• The more massive the star, the
more it crushes atoms in the center
and raises their temperature
• The hotter/denser the star, the
faster the nuclear reactions occur 
The sooner it burns out
– Some stars can last as little as a
hundred million years
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 47
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Topic 2: Stars
Death of Very Massive Stars
• If the star is much more massive
than our Sun it runs out of fuel
quickly
– 1x Sun  ~10 billion years
– 10x Sun  ~30 million years
– 100x Sun  ~100,000 years
• Different things happen as it runs
out of fuel  gravity is so strong it
Big Bang,
Massive Things:
Galaxies,
and Black Holes 48
can Black
REALLY
crush
theStars
star
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Topic 2: Stars
More Crushing  Neutron Star
• After the fuel runs out, if the mass of
the star is large enough, gravity crushes
the atoms into each other
• The electrons are pushed so close to the
protons that they start to interact
– Turn into Neutrons (more on the
physics of this interaction in Chapter
19)
• The star turns into a giant ball of
neutrons about the size of Manhattan
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 49
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Topic 2: Stars
Creating Neutron Stars
Proton + Electron  Neutron + Neutrino
Neutrino
(leaves
the star)
Electron
Up Quark
Down Quark
Down Quark
Up Quark
Proton
Neutron
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 50
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Topic 2: Stars
Neutron Stars
• Neutrons don’t like to be “too close” to
each other because of Quantum
Mechanics  star can stabilize
• In this process the star has collapsed
from the size of the Earth into a ball of
neutrons just a few kilometers across
• Incredibly dense!
– Billions of tons per cubic inch
– A marble made from neutron star
material would weigh the same as the
Earth
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Black Massive Things: Galaxies, Stars and Black Holes 51
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Topic 2: Stars
The crushing…
• The inner part of the star is
quickly crushed into a neutron
star
• What happens to the outer
part? Falls towards the center!
• Hits the dense neutron core and
bounces back into space as a
giant
explosion
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes
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Topic 2: Stars
52
Huge Explosion = Supernova
• The explosion can be so big that it can
shine as bright as 10 billion suns for a
couple of weeks
• The temperatures in the explosion are so
high and the atoms are so densely
packed that really heavy atoms can be
created and then blown into space
– This is how we get stuff like uranium
on the Earth
• We call the “remnants” of supernovas
“nebulae”
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 53
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Topic 2: Stars
Moving Towards Black Holes
• If the remaining neutron star
has a “critical mass” (about
3MSun) it can continue to collapse
• Nothing left to oppose the crush
of gravity!  Continues to
collapse until it becomes a Black
Hole
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 54
Holes, No Math
Topic 2: Stars
For Next Time – L22
• Reading:
– (Unit 5)
• Pre-Lecture Reading Questions:
– Unit 5 Revision (if desired): Stage 1
• End-of-Chapter Quizzes:
– Chapter 16 if we finished Chapter 16 (else just
Chapter 15)
• Papers:
– Paper 3 Revision (if desired): Stage 1 due
Wednesday
• Honors Papers:
– (Stage 2)
– Final paper due on the last day of class
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 55
Holes, No Math
Topic 2: Stars
For Next Time – L23
• Reading:
– (Unit 5)
• Pre-Lecture Reading Questions:
– Unit 5 Revision (if desired): Stage 2
• End-of-Chapter Quizzes:
– Chapter 16 if we finished Chapter 16 (else just
Chapter 15)
• Papers:
– Paper 3 Revision (if desired): Stage 1 due
Wednesday
• Honors Papers:
– (Stage 2)
– Final paper due on the last day of class
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 56
Holes, No Math
Topic 2: Stars
Full set of Readings So Far
•Required:
–BBBHNM: Chaps. 1-17
•Recommended:
– TFTM: Chaps. 1-5
– BHOT: Chaps. 1-7, 8 (68-85), 9
and 11 (117-122)
– SHU: Chaps. 1-3, 4(77-93),
5(95-114), 6, 7 (up-to-page 159)
– TOE: Chaps. 1-3
Big Bang, Black 57
Massive Things: Galaxies, Stars and Black Holes
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Topic 2: Stars
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 58
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Topic 2: Stars
Clicker Question
Why do stars shine?
a) When atoms fall back to their
lowest energy level, they give off
light
b) Gravity is pushing atoms to fuse
c) Nuclear reactions
d) Heavy nuclei
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 59
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Topic 2: Stars
Clicker Question
What is the main reason the atoms in a star
don't just all fall to the center of the star?
a) Because of the surface of the star keeps
them from falling to the center the same way
the surface of the Earth keeps things from
falling to the center
b) Because all the other atoms are in the way
c) Because of the pull of gravity
d) None of the above
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 60
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Topic 2: Stars
Clicker Question
What are the two main
interactions in stars and how do
they relate to each other?
1. Gravity and nuclear fusion
2. Gravity and degeneracy
pressure
3. Nuclear fusion and degeneracy
pressure
Big Bang,
Black Massive Things: Galaxies, Stars and Black Holes 61
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Topic 2: Stars
The Life of a Star Continued…
As the hydrogen gets used up the
core “ball” becomes a smaller
ball of mostly helium
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 62
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Topic 2: Stars
The “Burning” Process
• At the beginning of a stars life,
most of the atoms are hydrogen 
they get converted to helium first
• Then the helium starts getting
converted into heavier elements like
carbon, oxygen and iron
 Produces many of the heavy
elements that will go into the
universe after it dies
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 63
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Topic 2: Stars
Death of Stars
When the hydrogen
“fuel” runs out different
things happen for very
massive stars and small
mass stars separately
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 64
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Topic 2: Stars
Next look at the
nuclear reactions that
keep the star from
getting “crushed” by
gravity
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 65
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Topic 2: Stars
Prep for Next time – L23
• Reading:
– Chapter 18
• Pre-Lecture Reading Questions:
– Chapter 18
• End-of-Chapter Quizzes:
– If we finished Chapter 16 then end-ofchapter quiz 16 (else just through
Chapter 15)
• Papers:
– Paper 2 Revision: Was due before class
today. Let us know if you were mis-graded
– Paper 3: Calibrations, reviews and SelfBig Bang,
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Things:
Galaxies, Stars
and Black
Holes 66
assessment
Wednesday
before
class
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Topic 2: Stars
Was due Today – L24
• Reading:
– Chapter 18
• Pre-Lecture Reading Questions:
– Chapter 18
• End-of-Chapter Quizzes:
– Chapter 15 was due, but I’ll give extensions since
Chapter 14 was busted.
– You need to go back and check Chapter 14. Many
of you need to go back and fix the wrong
answers you were accidentally getting credit for
• Papers:
– Paper 3: Was due today. One of the calibrations
was busted. I’ll fix that soon. After I do that,
I’ll open up a chance for Revisions
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 67
Holes, No Math
Topic 2: Stars
Prep for Next time – L24
• Reading:
– Chapter 18
• Pre-Lecture Reading Questions:
– Chapter 18
• End-of-Chapter Quizzes:
– If we finished Chapter 16 then end-of-chapter
quiz 16 (else just through Chapter 15)
– You need to go back and check Chapter 14. Many
of you need to go back and fix the wrong
answers you were accidentally getting credit for
• Papers:
– Paper 3: Was due today. One of the calibrations
was busted. I’ll fix that soon. After I do that,
I’ll open up a chance for Revisions
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 68
Holes, No Math
Topic 2: Stars
Prep For Next Time – L10
• Note: May change depending on how far we get in
lecture
• Reading:
–BBBHNM: All reading through Chapter 18
• Reading Questions:
– All reading questions through 18
• eLearning Quizzes:
– If we finished Chapter 16 then end-of-chapter
quiz 16 (else just through Chapter 15)
• Papers:
– Paper 3 revisions text (if desired) due before
class on Monday
– Paper 2 revisions (if any) calibration, reviews and
self-assessment due before class on Monday
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 69
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Topic 2: Stars
Was due today– L11
• Reading:
–BBBHNM: All reading through Chapter 18
•Reading Questions:
– All reading questions through 18
• eLearning Quizzes:
– Through Chapter 16
• Papers:
– Text of Paper 3 revisions (if desired) were
due before class
– Paper 2 revisions (if any): calibration,
reviews and self-assessment due before
class
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 70
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Topic 2: Stars
Prep for Today (Is now due) – L22
• Reading:
– BBBHNM 17
• Reading questions:
– Chapter 17
• End-of-Chapter Quizzes:
– Chapter 15
• Paper Stuff
– Paper 2 Revision: Calibrations and Review
were due before class
– Paper 3: Calibrations and Review were due
before class
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 71
Holes, No Math
Topic 2: Stars
Prep For Next Time – L11
• Note: May change depending on how far we get in
lecture
• Reading:
–BBBHNM: All reading through Chapter 19
• Reading Questions:
– All reading questions through 19
• eLearning Quizzes:
– If we finished Chapter 16 then end-of-chapter
quiz 16 (else just through Chapter 15)
• Papers:
– Rest of Paper 3 assignment (if you resubmitted)
due before class on Tuesday
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 72
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Topic 2: Stars
Prep for Next Time – P21
• Reading
– BBBHNM 17
• Reading questions
– Chapter 17
• End-of-Chapter Quizzes
– If we finished Chapter 16 then end-of-chapter
quiz 16 (else just 15)
• Papers
– Paper 2 Revision: Calibrations and Review were
due before class
– Paper 3: Calibrations and Review were due before
class
– Paper 4: Will assign paper 4 next time
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes
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Topic 2: Stars
73
Prep for Next Time – P22
• Reading
– BBBHNM 17
• Reading questions
– Chapter 17
• End-of-Chapter Quizzes
– If we finished Chapter 16 then end-of-chapter
quiz 16 (else just 15)
• Papers
– Paper 2 Revision: Calibrations and Review were
due before class
– Paper 3: Calibrations and Review were due before
class
– Paper 4: Will assign paper 4 next time
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes
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Topic 2: Stars
74
Full set of Readings So Far
•Required:
–BBBHNM: Chaps. 1-17
•Recommended:
– TFTM: Chaps. 1-5
– BHOT: Chaps. 1-7, 8 (68-85), 9
and 11 (117-122)
– SHU: Chaps. 1-3, 4(77-93),
5(95-114), 6, 7 (up-to-page 159)
– TOE: Chaps. 1-3
Big Bang, Black 75
Massive Things: Galaxies, Stars and Black Holes
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Topic 2: Stars
Future: The Red Giant Phase
When most of the hydrogen is used
up, the core gets crushed
Helium falling towards the center
speeds up and interacts
Heats up the hydrogen in the outer
shell
Inflates to giant red shell that
emits red light
Big Bang,
Black Massive
Things:
Galaxies,
Black Earth
Holes 76
Bigger
than
the
sizeStars
ofandthe
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Topic 2: Stars
White Dwarf
Eventually the atoms get REALLY close to
each other and the strength of the
repulsion between the electrons from
quantum mechanics is so big that it
balances out the gravity
– Outer part is blown away
• Planetary Nebula
– Inner part stabilizes
• Call this a “White Dwarf”
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 77
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Topic 2: Stars
Shouldn’t a Star just Collapse?
• Why don’t the atoms just
fall to the center of the
star?
• Do they orbit?
• If the star is giving off
light aren’t the atoms
losing energy, so they
should fall in
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 78
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Topic 2: Stars
Today’s Lecture
•Galaxies Form
•Stars Form…
•Stars Die… and die
in different ways
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 79
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Topic 2: Stars
The life and death of our Sun
Our Sun will go through
a Red Giant phase in
about 5 billion years
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 80
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Topic 2: Stars
Our Sun Today
•Sun is using its
hydrogen to create light
•Helium produced falls to
the center (the core)
– Core is not hot enough
to convert helium into
Carbon
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 81
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Topic 2: Stars
For Next Time
Topics
• Galaxy Formation  Done
• Stars  Done
• Black Holes Next
Reading for Next time:
BBBHNM: Chap 17
Full reading for Unit 5:
• BBBHNM: Chaps. 1-17
• TFTM: Chaps. 1-5
• BHOT: Chaps. 1-7, 8 (68-85), 9 and 11 (117-122)
• SHU: Chaps. 1-3, 4(77-93), 5(95-114), 6, 7 (upto-page 159)
• TOE: Chaps. 1-3
Lecture prep: Turn in on eLearning
Two questions
fromGalaxies,
ChapterStars
17 you
to
Big Bang, Black
Massive Things:
and want
Black Holes
82
know
the
answer
to
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Topic 2: Stars
Shouldn’t a Star just Collapse?
• Atoms in stars give off
lots of light as energy
• If the atoms are losing
energy, why don’t they
just slow down and have
everything fall to the
center of the star?
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 83
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Topic 2: Stars
A giant lump of atoms?
• Why doesn’t everything
just fall to the center of
the Earth?
• The Earth is solid, but
stars aren’t
–Earth is made of iron and
heavy atoms
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 84
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Topic 2: Stars
The Reading So Far and For Unit 5
Reading for Unit 5:
• BBBHNM: Chaps. 15-17
• SHU: 4(87-93)
• TOE: 3
• BHOT: 8(76-85)
Full reading through Unit 5:
• BBBHNM: Chaps. 1-17
• TFTM: Chaps. 1-5
• BHOT: Chaps. 1-7, 8 (68-85), 9 and 11
(117-122)
• SHU: Chaps. 1-3, 4(77-93), 5(95-114), 6, 7
(up-to-page 159)
• Bang,
TOE:Black
Chaps.
1-3
Big
Massive
Things: Galaxies, Stars and Black Holes 85
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Topic 2: Stars
Other Stuff
• Q-Drop date is tomorrow
– No final
– Only papers 1-5 (due last day of
class)
• Elearning:
– Unit 5 in progress
• Make sure you pick up the latest
version of the online textbook!!!
Big Bang,
Black Massive
Things: Galaxies,
Stars
and Black Holes 86
–
Been
updating
it
all
semester
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Topic 2: Stars
Papers 1 and 2
• Paper 1 is done
• Paper 2 grades are on
eLearning
– Working on getting the
revised grades fixed
– Paper 2 Revision is done
Big 87
Bang, Black Massive Things: Galaxies, Stars and Black Holes
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Topic 2: Stars
Papers 3,4 and 5
• Paper 3:
– Let us know if you think you have been
mis-graded
– Revisions now open
• Paper 4:
– Assigned after we start Chap 17
– Probably today
– Due 1 week after we finish Chap 17
• Paper 5 (last paper, no final)
– Assigned after we start Chap 20
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 88
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Topic 2: Stars
Other Stuff
• Elearning:
–Unit 5 in progress
• Make sure you pick up the
latest version of the online
textbook!!!
–Been updating it all
semester
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 89
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Topic 2: Stars
Examples
• Our sun: Has another ~5
billion years before it goes
through a Red Giant Phase
• Others can last as little as
a hundred million years
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 90
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Topic 2: Stars
The Life and Death of Stars
Small Star
(Red Giant)
White Dwarf
Brown Dwarf
Big Star
(Supergiant)
Explodes
(Supernova)
Neutron Star
Black Hole
Slightly more complicated than this…
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 91
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Topic 2: Stars
Writing Assignments
Short Assignments 1 & 2
Re-do’s are still possible.
Want to revise again? Talk to
me
eLearning:
Unit 4 now due
Need to be working on Unit 5
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 92
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Topic 2: Stars
Papers AFTER Paper 2
Two options
1.Two short papers like the first one
• One on Black Holes (due one week
after we finish Black Holes)
• One on Dark Matter (due last day
of class)
2.Research Paper
If you want this option Stage 1 must
be approved ASAP
• Was due last week
• Final paper due the last day of
th
Big Bang, class,
Black Massive
Things: Galaxies,
Stars
and Black Holes 93
Tuesday
Dec
8
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Topic 2: Stars
For Next Time
• More on the properties of Black
Holes…
Full reading for Unit 5:
• BBBHNM: Chaps. 1-17
• TFTM: Chaps. 1-5
• BHOT: Chaps. 1-7, 8 (68-85), 9
and 11 (117-122)
• SHU: Chaps. 1-3, 4(77-93), 5(95114), 6, 7 (up-to-page 159)
• TOE: Chaps. 1-3
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 94
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Topic 2: Stars
Why do we call it
a black hole?
Look at objects
this big
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 95
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Topic 2: Stars
Escape Velocity
• The escape velocity for the
Earth is about 11.2 km/sec
• The escape velocity for the sun
is about 620 km/sec
• The escape velocity of a neutron
star is about half the speed of
light!
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 96
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Topic 2: Stars
Why do we call it a Black Hole?
A Black Hole is so dense
that it’s escape velocity
is GREATER than the
speed of light  light
can no longer escape!
More on this soon…
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 97
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Topic 2: Stars
Wait a Billion Years
After less than ~1 billion
years, galaxies and the first
stars start to form
Formation of
the first stars
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 98
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Topic 2: Stars
Remaining Lectures
• Two lectures left: Today and
Thursday
– Stars and Black Holes
– Won’t get back to Inflation and
Dark Energy (Lectures posted)
• Recitation tomorrow as usual
• Extra recitation at the Dixie
Chicken at 2:00 PM tomorrow
(Wednesday)
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes 99
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Topic 2: Stars
Remaining Assignments
• Writing Assignments Due Thursday
– However, you may turn it in, via
email, on Monday
– If you want to revise your paper
you’ll need to pick it up from me
directly
• Don’t forget to finish your WebCT
stuff
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes100
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Topic 2: Stars
• Textbook?
• BHOT 8 starting on page 76.
• SHU 4, 5
• SHU 8 for MACHOs (need this?), 9 Dark Matter (Cold or hot?)
• SHU 10 is Quasars…
• SHU 11: In search of black holes
• TOE 3, 4
• TCP 17
Reading:
– TOE: 3
– BHOT: 8
– SHU: 4, 7
– TCP 16 and 17
– Others???
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes101
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Topic 2: Stars
Summary of the Buzz Words in the
Newspapers
• White Dwarf
• Brown Dwarf
• Neutron star
• Supernova
• Black Hole
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes102
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Topic 2: Stars
TCP 17 cont…
• Once the critical mass is
reached nothing can hold back
gravity and it collapses on itself
and becomes a black hole.
• This stretches space time
• Cool pictures on page 529
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Topic 2: Stars
TCP 17 cont…
• How black holes are formed
• A black hole originates in the collapse of the iron core
that forms just prior to the supernova of a very high
mass star
• Any star born with more than about 8MSun dies in a
supernova (previous lecture), but most of the star’s
mass is blown into space by the explosion.
• As a result most of the collapsed cores left behind by
most supernovae become neutron stars
• However, if the supernovae doesn’t blow away too
much of the mass the remaining neutron star can have
enough mass so that the neutron pressure cannot
overcome gravity
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Topic 2: Stars
• If the mass of the neutron star
is so large that the gravity can
overcome the neutron
degeneracy that the core will
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes105
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Topic 2: Stars
• This mass is about 3MSun
• Stars with 1½ times the mass of
the sun eventually can’t support
itself against its own gravity and
will collapse into a black-hole
• Chandrasekhar limit
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes106
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Topic 2: Stars
• Its as if we have a giant nucleus
of neutrons only it’s held
together by gravity not the
strong force
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes107
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Topic 2: Stars
• In some cases they may explode
or manage to throw off enough
matter to reduce their mass
below the limit
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Topic 2: Stars
TCP 17 cont…
• (again p514)
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes109
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Topic 2: Stars
Why is Iron Special? Need This
• For the elements lighter than iron: every
time you create a new, heavier nucleus,
you release energy
• For the elements heavier than iron: it
takes energy to create them (don’t
create light and doesn’t add to the heat
of the star that keeps it from
collapsing)
• Thus, after all the atoms have turned
into iron you can’t any more heat from
crushing atoms together to form heavier
atoms
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes110
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Topic 2: Stars
TCP 17 cont…
• Aside on neutron stars:
• As neutron stars collapse they start
spinning faster and faster (kinda like an
ice skater pulling her arms in)
• Picture from 218, chapter 10?11?
• It emits light along its axis (picture on
p527)
• We see this beam of light as it sweeps
past us. Kinda like a light house
• Figure on p527
• Give these the creative name of pulsars
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes111
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Topic 2: Stars
TCP 17 cont…
• Actually we have found neutron
stars that have planets orbiting
them… kinda cool
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes112
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Topic 2: Stars
• Weird stuff: more massive than
the sun but just about 10 Km
across, essentially a giant nuclei
but different
– Almost entirely neutrons (no
protons)
– Gravity, not the strong force,
holds it all together
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes113
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Topic 2: Stars
• If the mass of the star is one
or two times the mass of the
sun, the crush of gravity would
be repelled by the exclusion
principle between the neutrons
and protons, rather than
between the electrons
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes114
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Topic 2: Stars
TCP 17 cont…
• In the iron core (or if there is electron degeneracy) not really
sure which, and the gravitational pressure continues then the
electrons have enough energy such that that when they collide
with protons they convert into a neutron and a neutrino
• P511, Fig 16.16 (something better)?)
• The iron core with a mass comparable to our Sun (is this the
1.4?) and once the electrons are gone, they don’t have the
degeneracy pressure so gravity can start squeezing again making
the electrons and protons more energetic so they convert into
more neutrons until everything is just a just a bunch of neutrons
• The neutrons also have a degeneracy that opposes the collapsing
of gravity and our giant ball of iron that used to be the size of
the earth collapses into a ball of neutrons just a few kilometers
across
• Its as if we have a giant nucleus
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes115
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Topic 2: Stars
• Picture 17.2 (page 521)
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes116
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Topic 2: Stars
• Pictures on p507 and 8 of TCP.
Also 16.16
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes117
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Topic 2: Stars
The Birth of Stars
• Gravity condenses hydrogen and
helium into small clumps
• Atoms get close enough that they
start interacting with each other
• As the atoms collide with one
another we start to get nuclear
reactions
– “A Star is Born”
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes118
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Topic 2: Stars
• Sometimes when a very massive star
collapses, the outer regions may get
blown off in a tremendous explosion
called a supernovae
• Results in a great cloud of hot
shining dust blown out into space,
spreading all the elements far and
wide
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes119
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Topic 2: Stars
• Pressure
• TCP: Page 440, Fig S4.10
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes120
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Topic 2: Stars
– Supernovae
– White Dwarf
– Neutron Star
– Black hole…
– Pulsars
– Worm holes?
– MACHOS?
– Red Giants?
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes121
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Topic 2: Stars
• Another issue: Things speed
up as they fall towards the
center of the star: Just like
a rock falling towards the
earth speeds up  brings
energy into the star!
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes122
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Topic 2: Stars
• This is a test…
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes123
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Topic 2: Stars
• This is some text
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes124
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Topic 2: Stars
Neutron Stars
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes125
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Topic 2: Stars
• Nova video
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes126
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Topic 2: Stars
• This is some text
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes127
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Topic 2: Stars
• Don’t want to say too much here
about the exclusion principle,
eventually gravity can overcome
the quantum mechanical effect
of particles needing to not be in
the same position/velocity state
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes128
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Topic 2: Stars
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes129
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Topic 2: Stars
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes130
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Topic 2: Stars
Heat and pressure
• As the atoms are drawn towards the center of
the star they get faster (like a rock falling
towards the surface of the earth)
• As atoms combine in nuclear reactions they
release energy and the atoms get more
energetic
• These higher energy atoms can try to escape
the gravity of the star
• Can think of this like a gas: If the atoms are
getting more energetic we say they are being
heated
• As they atoms get more energetic (higher
velocity) they can get further from the center
of the star, again the same analogy as
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes131
throwing a rock from Topic
the 2:
surface
of the earth
Holes, No Math
Stars
• When the “gas” of energetic atoms gets heated its as
if there is a “pressure” pushing the atoms away from
the center like a balloon. If you heat up a balloon (or
put more air in it) the atoms hit the walls of the
balloon harder and we say it is under more pressure.
What keeps the balloon together is the force that the
plastic walls of the balloon exerts; what keeps the
star together is the force of gravity pushing the
atoms back towards the center of the star
• We say that gravity exerts a “pressure” on atoms in
the star
• In a balloon, the inward pressure of the balloon walls
balances the outward pressure of the gas. In a star
gravity the pressure of gravity balances the outward
pressure of the gas
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes132
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Topic 2: Stars
• Probably want to finish the
story about neutron stars and
white dwarfs and such… That
could also go into the next
section…
• Next some SHU 4 cont stuff..
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes133
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Topic 2: Stars
Stellar Cooking
• The hydrogen effectively gets
converted into helium and releases
lots of energy in the form of
photons, electrons and neutrinos
• The heat released in this reaction,
which is like a controlled hydrogen
bomb explosion, is what makes a
star shine
• Raises the temperature of the star
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes134
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Topic 2: Stars
SHU 4
• Probably want that astronomy
book that did the different
types of stars…
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes135
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Topic 2: Stars
• After this fuel is spent the
center can collapse into a very
dense state such as a black
hole… Are we getting into the
next section?
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes136
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Topic 2: Stars
Big Picture
• The big picture about galaxy
formation, stellar formation and
a star’s life is the balance
between the stuff that tries to
compress it together and the
stuff that keeps it from
crushing itself into a tiny little
thing.
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes137
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Topic 2: Stars
Gravity
• Let’s use the earth as an example.
Let’s say I have a rock near the
surface of the earth. That rock will
fall to the surface of the earth.
• Its been attracted
• This is true for all objects near the
earth. They fall towards the center
of the earth
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes138
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Topic 2: Stars
Other?
• Ok… So all the things on the earth fall
to the center of the earth… why doesn’t
our rock fall to the center? Because it
hits the ground.
• So what?… what about the ground keeps
it from falling to the center? I.e., what
force OPPOSES gravity and keeps it
from falling further? Why doesn’t the
stuff already at the surface of the
earth fall more? Why is the SURFACE
of the earth not falling towards the
center?
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes139
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Topic 2: Stars
Opposition
• The reason it doesn’t fall towards the center
of the earth is that the “stuff” of the ground
“pushes back”
• How does it push back?
• The atoms of the stuff that make up the
earths surface are bound together (this is
chemistry in some real sense)
• For the rock to “pass through” the surface
would mean having to break the bonds that
hold the atoms together
• These bonds can be VERY strong
• The bonds in the atoms of paper are much
weaker than the bonds of steel
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes140
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Topic 2: Stars
Summary
• So… The surface of the earth is where it is
because gravity is pushing it towards the
center, but the stuff below the surface is
“pushing back” since the push of gravity isn’t
strong enough to break the bonds of the stuff
below it
• If the bonds weren’t strong (but did exist)
like in water, if the rock hit water it would
fall through the water until it hit something it
couldn’t fall through.
• Bottom line: What’s important is that gravity
causes things to compress and some other
force keeps things from compressing
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes141
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Topic 2: Stars
Galaxy Formation (BHOT 8
continued)
• Galaxy formation:
• After the big bang we just had lots
of stuff floating around in space
• Can think of this as just being a
giant tank of gas.
• After a few million years the
electromagnetic attractions
(electrons to nuclei) would start
forming atoms (already said this)
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes142
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Topic 2: Stars
• The gravitational attraction would eventually stop expansion in
some regions and start them to collapse
• As they were collapsing, the gravitational pull of matter outside
these regions might start them rotation slightly
• As the collapsed region got smaller, it would spin faster– just like
ice skaters spin faster on ice as they draw in their arms.
• Eventually, when the region got small enough it would be spinning
fast enough to balance the attraction of gravity to balance the
attraction of gravity and in this way, we believe, disk-like
rotating galaxies were born Others would form other times of
galaxies like elliptical galaxies.
• In this manner the clouds coalesce into starts like our sun,
burning hydrogen into helium and radiating the resulting energy as
heat and light
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes143
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Topic 2: Stars
Star Formation (TOE 3… BHOT 8
cont…)
• As time went on the hydrogen and helium gas in the
galaxy would condense under their own gravity
• This would create proto-stars. Read: effectively a
ball of gas in space, just concentrated in one area
because of the gravitational attraction
• As these contracted (again by gravity), the atoms
would collide with one another
• As things fell to the “center” their speed would
increase (like a ball falling to the surface of the
earth picks up speed) the temperature would increase
until eventually it became hot enough (particles are
energetic enough) to start nuclear fusion reactions
(i.e., when they collide)
• Picture of a fusion reaction that converts hydrogen
into helium and releases a lot of light (photons)
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes144
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Topic 2: Stars
• These would convert the hydrogen
to make more helium. The heat
released in this reaction, which is
like a controlled hydrogen bomb
explosion, is what makes a star
shine.
• Pictures on p507 and 8 of TCP. Also
16.16
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes145
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Topic 2: Stars
Star Formation (BHOT 8 cont…
TOE 3)
• This additional heat also increases the
pressure of the gas until it is sufficient
to balance the gravitational attraction
and the gas stops contracting
• In this manner the clouds coalesce into
starts like our sun, burning hydrogen
into helium and radiating the resulting
energy as heat and light
• This can stay stable for billions of years
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes146
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Topic 2: Stars
BHOT 8 cont…
• Our star: Can last for another 5
billion years or so
• Others can last as little as a
hundred million years
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes147
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Topic 2: Stars
BHOT 8 cont…
• What happens when the star starts to run out of
fuel?
• Since there isn’t enough hydrogen around to keep
making helium at a fast enough rate, the heat can’t
keep the gravity off any more and the star starts to
contract (i.e., get smaller)
• This causes the atoms closer together and the star
gets hotter again and we burn even the remaining
hydrogen
• What happens when the hydrogen is all gone and all
we have left is the helium produced from fusion?
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes148
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Topic 2: Stars
• Instead of converting hydrogen to helium
(because there isn’t much hydrogen
left), the helium starts interacting
(again chemistry) and gets converted
into heavier elements like carbon and
oxygen (this is where the carbon and
oxygen in the universe comes from).
Need a picture here
• After this fuel is spent the center can
collapse into a very dense state (white
dwarf, neutron star or a black hole)
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes149
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Topic 2: Stars
TCP 17
• Do we have enough on stellar
formation?
• The afterworld of stars: White
dwarfs, neutron stars and black
holes
Big Bang, Black Massive Things: Galaxies, Stars and Black Holes150
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Topic 2: Stars
• Paradoxically: the more fuel a star starts off
with the sooner it runs out. This is because
the more massive the star is the hotter it
needs to be to balance its gravitational
attraction. And the hotter the star the faster
the nuclear reactions occur and the sooner it
will use its fuel
• Important point: Because the strength of the
force of gravity depends on the mass of the
star (and so in effect on its size and weight)
the star’s fate depends on its size
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• Then the star life cycle starts and the
hydrogen burns and turns into helium
• As the hydrogen gets used up
gravitational pressure increases and the
helium starts to fuse
• One by one the heavier elements are
produced, each in turn fueling reactions
to produce the heaviest element as
gravity compresses the star into a
denser and denser mass
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TCP 17 cont…
• The battle between the “crush”
of gravity and the outward
pressure of the nuclear burning
that governs a star’s life
• Here we talk about what
happens as that fuel begins to
run out
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TCP 17 cont…
• Start with small stars (kinda did
this already), like our sun
• After all the nuclear burning all
we are left with is the products
of the burning
• Typically this is carbon
• Slightly bigger ones will be able
to crate iron
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• Since it happens in roughly
the same way, they all look
the same
• Since we measure the amount
of light we can tell how far
away it occurred
• This is pretty damn cool!
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Topic 2: Stars
TCP 17 cont…
• Theoretical calculations show that a
white dwarf cannot be larger, in mass,
1.4 Sun
• This is the Chandrasekar limit
• At this mass the compression is so big
that the electrons get so fast that they
approach the speed of light
• Unfortunately, they can’t get any
fasters than light so the game breaks
down
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TCP 17 cont…
• After 1.4 MSun gravity is stronger
than the electron degeneracy
pressure and the star collapses
further, heating the star until the
temperature is big enough for
carbon fusion
• The star explodes in a White Dwarf
Supernova
• Not sure how this ends…
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Topic 2: Stars
•
•
Mention the difference between
massive star supernovae and the
“carbon bomb” white dwarf supernovae
White dwarf supernovae are especially
cool because they always happen when
the WD reaches the critical mass of
1.4MSun when you get the carbon bomb
stuff and the thing explodes (we call
this a type 1a supernova)
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Death of White Dwarf’s
• Depending on its size, once iron
is formed in the star, it either
dies slowly and sheds its
elements into space
– Why does it sped its elements
into space?
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Stuff on Electron Degeneracy
• Do we want an aside about degeneracy?
• Since there is no burning to counteract
the gravity it shrinks until the electrons
get so close together that, for quantum
mechanical reasons, they can’t get any
closer (electron degeneracy)
• A white dwarf is supported by the
exclusion principle repulsion between
electrons in the matter
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TCP 16 and 17 Continued
• This incredible compression
releases a huge amount of
energy and is what we call a
supernova
• (It can shine so brightly that it
looks like about 10 billion suns
for about a week)
• Page 114
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Topic 2: Stars