Big Bang, Black
Holes, No Math
ASTR/PHYS 109
Dr. David Toback
Lecture 12
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Was due Today – L12
• Reading:
– (BBBHNM Unit 2)
• Pre-Lecture Reading Questions
– Unit 1 Grades: If you received a Contact Instructor, send
me an email. Will work with you.
– Let us know if you were misgraded on any assignments
• End-of-Chapter Quizzes:
– End-of-Chapter Quiz 7a & 7b
• Paper 1:
– (Stage 2 due Wednesday before class in CPR)
• Make sure you have submitted to both CPR and turnitin
on eCampus
• Honor’s Paper:
– Stage 1: Due March 7th. You should have your source
materials and be finishing reading them soon
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Heads Up: Paper 2
• What is the
evidence that
Stars are
made of
Atoms?
• This will be
the topic of
Paper 2
• In order to
understand the
evidence, we
next talk about
Atoms and how
they work
• Will be assigned
after we finish
Chapter 8
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Outline for Unit 2: Physics We Need
1. Light and Doppler Shifts Done
2. Gravity, General Relativity and
Dark MatterDone
3. Atomic Physics and Quantum
Mechanics Done
4. Nuclear Physics and Chemistry 
This time
5. Temperature and Thermal
Equilibrium
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Looking at the Lights in the Sky
What we know about
the universe comes
from multiple places
So far:
• Learned about the
light coming from
the sky
• Learned that atoms
can produce this
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Big light
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Questions We’re Trying to Answer
• What are stars made of?
• What can we learn from
looking at them?
• How do we know? What is
the evidence
Today: More about
different types of atoms
that produce the light
 A “smoking gun” piece of
evidence that the light
from the sky is from
atoms out there
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Outline
• Overview
• What protons and neutrons are
made of: Quarks
• How protons and neutrons interact
& combine to form a nucleus
• Chemistry
• Spectral lines
– Light from stars!
• Learning about the stars
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Overview of the story
• Big things are made from LOTS of small things
• Small things: The Fundamental Building Blocks of Nature
– What is the “stuff” in atoms
• ElectroMagnetism (electric charge)
– What holds electrons and protons together
• Quantum Mechanics
– Why atoms form the way they do
– Electron in orbits
– Atoms absorbing and emitting photons (light)
• Different TYPES of Atoms
– The Strong Force
– Keeping protons and neutrons together (atomic nuclei)
– Nuclear Physics and Chemistry
– Different atoms  Different light…
• Studying the Stars using their light
– Spectral lines of the atoms
– Atomic “fingerprints”
– The light we see from the stars
Physics We Need
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Last
Lecture
This
Lecture
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Smaller Building Blocks of Nature
• Atoms are made of a
nucleus surrounded by
electrons
–Many types of nuclei
–Only one kind of
electron
• Nuclei is composed of
neutrons and protons
–Neutrons and protons
are two different types
of nucleons
• Nucleons are made of
quarks
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Chemistry
• We can put
nucleons
together in lots
of different
ways…
• Each different
way corresponds
to a different
type of atom
Knew about the periodic table in
the 19th century
Understood it was just
combinations of protons and
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neutrons in the 1920’s 10
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Observation: Different Kinds of Atoms
• The kind of atom
depends on the
number of protons
in the nucleus
• Helium (He), with
2 protons, 2
neutrons and 2
electrons
Different
numbers of
neutrons ↔
different
isotopes
Helium 4
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Why do nucleons stick together?
• If what holds the atom
together is the opposite charge
of the protons and the
electrons…
Why don’t the same sign
charges of the protons “blow
the nucleus apart?”
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What Nucleons are Made Of
• Each nucleon is
made of 3 quarks
• Two different
types of quark
• Called “up” quarks
and “down” quarks
• Each quark has
fractional charge
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More to say
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this later
Topic 4: Nuclear Physicsabout
& Chemistry
What holds the quarks together?
• The strong force
holds the quarks
together inside
the nucleon
• The force
mediator is the
“gluon”
– Quarks talk to
each other via
gluons
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The Answer
The same strong
force keeps the
nucleons together
Essentially the
gluons “leak” out
of the nucleons
and provide the
attractive force
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So what?
• Why do we care about all the
different kinds of atoms?
• What does this have to do with
Stars and the Big Bang?
• The different mass and charge of
each nucleus means that each as a
different set of energy levels
– Each one has unique fingerprints!
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Different energy levels for each different
type of atom
Fingerprinting
the different
atoms
Hydrogen
Helium
Boron
Can use light of different energies
to identify atoms: Different Colors
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Atomic Fingerprints
• Each atom produces
a large number of
different
wavelengths with
VERY SPECIFIC
values
• Quantum Mechanics
predicts ALL of them
• If you see all the
ones you expect and
none you don’t, that
gives you confidence
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More on Fingerprinting
• Look at light from a
light bulb with
Hydrogen gas in the
way
• Different lines will
be absorbed by
Helium
• Can now identify a
mystery gas!
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Overview of the story
• Big things are made from LOTS of small things
• Small things: The Fundamental Building Blocks of Nature
– What is the “stuff” in atoms
• ElectroMagnetism (electric charge)
– What holds electrons and protons together
• Quantum Mechanics
– Why atoms form the way they do
– Electron in orbits
– Atoms absorbing and emitting photons (light)
• Different TYPES of Atoms
– The Strong Force
– Keeping protons and neutrons together (atomic nuclei)
– Nuclear Physics and Chemistry
– Different atoms  Different light…
• Studying the Stars using their light
– Spectral lines of the atoms
– Atomic “fingerprints”
– The light we see from the stars
Physics We Need
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Last
Lecture
This
Lecture
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Using Light From Stars
•Can look at the light
from the stars to
“see” if they are
made of atoms
•Figure out what
TYPE of atoms…
•How stars are
formed…
•What makes them
shine…
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What is a Star?
• Our best understanding is that
stars are great big balls of
(mostly) hydrogen gas
• The hydrogen interacts and
produces the light we see
– Makes them shine…
• What is the evidence for this?
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Stars
• What would happen
inside a giant ball of
hydrogen?
– Interactions
• What would it look
like to us?
– Light from the
interactions
– Next look at
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interactions
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Hydrogen Interactions
Proton
Proton + Proton
 Deuterium + Anti-Electron + Neutrino
Nuclear
Reaction
AntiElectron
Deuterium
Neutrino
Proton
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The Deuterium, neutrino and the AntiPhysics We Need
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Electron
get
energy
in
the
reaction
Topic 4: Nuclear Physics & Chemistry
More interactions
Deuterium
Proton + Deuterium  Helium3 + Photon
Photon
Nuclear
Reaction
Helium3
Proton
Physics
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Photon
canWe
have
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energy
Creating Stable Helium
Helium3
Helium3 + Helium3  Helium4 + 2 Protons
Nuclear
Reaction
Proton
Helium4
Helium3
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Proton
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Stars
• Nuclear interactions in the center of
the star create lots of energy which is
eventually emitted as light from the
surface of the star
– Shines white (or yellow)
• This light passes through other atoms
of the star
– Light is “absorbed” by the outer
atoms  Spectral lines
• Tells us what the stars are made of
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Looking at the Stars
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Analyzing Absorption Spectra
• Each element produces a specific set of
absorption (and emission) lines
• Using this information, we can study the
composition of stars
See only
spectral
lines for
known
atoms
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Remarkable…
• The Sun and stars are mostly
made of Helium and Hydrogen
• Our Sun is made of the same
stuff as all the other stars!
• The stuff out in the universe is
made of the same stuff that is
found here on Earth!
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Even More Remarkable
If all the stuff “out there” looks the
same as the stuff here on Earth then:
–The particles out there (electrons,
protons, photons etc.) are the same
as they are here
– The laws of physics that govern
putting together protons, nuclei and
atoms are likely to be the same
everywhere!
– Provides evidence that it’s been this
way for billions of years!
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Now that we know what
stars are made of and
what they are SUPPOSED
to look like, can we learn
anything else?
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•What if the stars
were MOVING?
•Can we tell? Yes!
Doppler effect
How?
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Atoms with Different Speeds
• If an atom emits a photon it
will correspond to an energy
that reflects the change of
two energy levels
• However if the atom is
MOVING the light will be
shifted to a different color
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Observing an Atom
Atom Emitting Light
Not Moving
Moving to the right
Can use this to study the motions of
the stars
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Looking at the Stars
Provides additional
evidence stars are made
of atoms
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Lecture on Chapter 8
now complete
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Paper 2
• Abbreviated description: What is the evidence that
Stars are made of Atoms?
– More detail on CPR, you REALLY need to read ALL
the instructions
• Explain it to someone who isn’t taking the class (no
jargon)
• Format:
– Introduction paragraph
– ~1 paragraph per piece of evidence
– Conclusion paragraph that ties it together
– http://faculty.physics.tamu.edu/toback/109/WritingAssignmen
ts/samplepaper.shtml
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Phase I and Phase II in CPR
Phase I: (Due 1 week after we finish Chapter 8)
• Submit online two ways: CPR and turnitin.com
Phase II: (Due one week after Phase I)
• Three-Part Calibrations/Reviewing
1. Calibrations, learning to use the Rubrics
2. Grade three other papers
3. Grade your own paper
Want feedback before you submit? Get it to
the TA on eCampus by Friday for guaranteed
feedback.
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Outline for Unit 2: Physics We Need
1. Light and Doppler Shifts Done
2. Gravity, General Relativity and
Dark Matter Done
3. Atomic Physics and Quantum
Mechanics Done
4. Nuclear Physics and Chemistry 
Done
5. Temperature and Thermal
Equilibrium  Next time
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Prep For Next Time – L12
• Reading:
– (BBBHNM Unit 2)
• Pre-Lecture Reading Questions
– Unit 1 Grades: If you received a Contact Instructor, send
me an email. Will work with you.
– Let us know if you were misgraded on any assignments
• End-of-Chapter Quizzes:
– If we finished Chapter 8 then End-of-Chapter Quiz 8
(else, just 7a and 7b)
• Paper 1:
– Stage 2 due Wednesday before class in CPR
• Make sure you have submitted to both CPR and turnitin
on eCampus
• Honor’s Paper:
– Stage 1: Due March 7th. You should have your source
materials and be finishing reading them soon
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Full set of Readings So Far
•Required:
– BBBHNM: Chap 1-9
•Recommended:
– BHOT: Chap. 1-6, 9 and 11
(117-122)
– SHU: Chap. 1-3, 6 and 7 (upto page 153)
– TOE: Chap. 1
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Clicker Question
A star is observed with the following light
pattern. Which way is it moving?
a) Towards us, slow speed
b) Away from us, slow speed
c) Towards us, high speed
d) Away from us, high speed
e) Stationary
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Clicker Question
Which best describes the two galaxies below?
a) Both are moving towards us, but the left one is
moving faster than the one on the right
b) Both are moving towards us, but the right one is
moving faster than the one on the left
c) Both are moving away from us, but the left one is
moving faster than the one on the right
d) Both are moving away from us, but the right one is
moving faster than the one on the left
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Clicker Question
A hydrogen atom is hit by a photon and the electron
absorbs the photon and moves to an excited state.
Later, a photon with the exact same energy is emitted
from the atom, and the electron moves back to its
original state.
Is this the same photon as before?
a) Yes, it was inside the electron
b) Yes, it was bouncing around inside the atom
c) No, the electron “destroyed” the original photon and
created the new photon
d) No, the nucleus “destroyed” the original photon and
created the new photon
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Clicker Question
As far as we know, Dark Matter
exists:
a) Everywhere in the universe
b) Only near black holes
c) Mostly in or around galaxies
d) It doesn't exist
e) We don't know where it
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exists
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Clicker Question
A man shoots a red photon straight up
into the air next to a very tall
building. The photon rises in the air.
Which statements are true:
a) The photon slows down as it rises,
the same way a rock would
b) The photon loses energy, the same
way a rock would
c) The photon gets blue-shifted
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Clicker Question
Instead of throwing a rock into the air, a man shoots a red photon straight up
into the air next to a very tall building. The following question are about the
photon when it reaches the top of the building. Which of the following
statements are true
Question 1: Speed
a) The speed of the photon stays the same
b) The speed of the photon slows down like a rock would
Question 2: Energy
a) The energy of the photon stays the same
b) The energy of the photon gets lower (like the kinetic energy would for a rock)
c) The energy of the photon gets larger (since it is getting closer to outer space)
Question 3: Color
a) The color of the photon stays the same
b) The color of the photon becomes more red (gets a longer wavelength)
c) The color of the photon becomes more blue (gets a shorter wavelength)
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Clicker Question
Two mystery galaxies (on the right) only have a single
spectral line in the visible spectrum as shown below.
If the above galaxy is stationary, which way is the
below galaxy moving?
a) Towards us
b) Away from us
c) It is also stationary
d) Not enough information
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Extra Credit
• Still offering extra credit for people
who find typos in the Textbook
• Extra credit for people who find
mistakes for any/all eCampus quizzes
or CPR assignments
• Now offering extra credit for students
who send good clicker questions. If it
becomes the basis for one used in class
I will give you extra credit
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Was due Today – L13
• Reading:
– (BBBHNM Unit 2)
• Pre-Lecture Reading Questions:
– Let us know if you were misgraded
– Unit 1 in CPR
• You MUST pass this portion to pass the class
• Grades on eCampus, Contact me if you haven’t passed
yet (additional quizzes needed)
• End-of-Chapter Quizzes:
– Chapter 7a & 7b quizzes
• Paper 1:
– (Stage 2 is due Monday before class)
– (Text needs to be in turnitin on eCampus)
• Honors Paper:
– Stage 1 due March 11th
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Prep For Next Time – L6
• Final
• Reading:
–BBBHNM: All reading through Chapter 10
•Reading Questions:
– All reading questions through 10
• eLearning Quizzes:
– Chapter 7
• Paper 2:
– Calibrations and grading if you didn’t pass
Paper 1, due before class on Monday
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Prep for Next Time – L12
•
•
•
•
•
Reading:
– (BBBHNM Unit 2)
Pre-Lecture Reading Questions:
– Let us know if you were misgraded
– Unit 1 Grades Posted in eCampus, contact if needed
End-of-Chapter Quizzes:
– If we finished Chapter 8 then end-of-chapter quiz 8 (else just up to
Chapter 7a & b)
Papers:
– Paper 1:
• Stage 2 is due before class on Monday
• (Text needs to be in turnitin on eCampus)
– Paper 2:
• If we finished Chapter 8, Stage 1 is due Monday before class
• Also due in turnitin
Honors Paper:
– Stage 1 due Wed March 11th
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Prep for Next Time – L13
•
•
•
•
•
Reading:
– (BBBHNM Unit 2)
Pre-Lecture Reading Questions:
– Let us know if you were misgraded
– Unit 1 Grades Posted in eCampus, contact if needed (more quizzes to
take)
End-of-Chapter Quizzes:
– If we finished Chapter 8 then end-of-chapter quiz 8 (else just up to
Chapter 7a & b)
Papers:
– Paper 1:
• Stage 2 is due before class on Monday
• (Text needs to be in turnitin on eCampus)
– Paper 2:
• If we finished Chapter 8, Stage 1 is due Monday before class
• Also due in turnitin
Honors Paper:
– Stage 1 due Wed March 11th
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Tentative Due Dates
•
•
•
•
•
•
•
•
Monday March 4th (Today)
– Paper 1 revisions due
– Paper 2 assigned
Monday March 11th
– No class, Spring Break.
– Want feedback on a Paper 2 draft? Due today in eLearning
Monday March 18th
– Paper 3 Assigned
– Reading for Chap 11 and 12, EOC quizzes for 9 due
Tuesday March 19th
– Paper 2 Text due in CPR and eLearning (1-day extension)
Friday March 22nd
•
Want feedback on a Paper 2 draft? Due today in eLearning
Monday March 25th
– Paper 2 Reviews due in CPR
Wednesday March 27th
– Paper 3 text due in CPR and eLearning (2-day extension)
Monday April 1st
– Paper 3 Reviews due in CPR
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Prep for Next Time – P11
• Reading:
– BBBHNM 9
• Reading questions:
– Chapter 9 or the recommended reading
• End-of-Chapter Quizzes:
– If we finished Chapter 8, end-of-chapter
quiz due before next class (else just 7)
• Papers:
– Paper 1 Resubmissions:
• CPR Calibrations due Monday
– Start working on Paper 2
• Paper 2 due Monday in CPR/Turnitin.com
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Prep For Next Time – L13
• Note: May change depending on how far we get in lecture
• Reading:
– BBBHNM: All reading through Chapter 9
• Pre-Lecture Reading Questions:
– Through Chapter 9
• End of Chapter Quizzes:
– If we finished Chapter 8 then end-of-chapter quiz 8 (else
just up to Chapter 7)
• Papers:
– Paper 0: Was due Friday. Pass/Revise grades will be posted
by the end of the night or after all regrades
– Paper 0 Revision (if necessary – See eCampus score, not
CPR Score): Open now, Text due Monday before class. All
Calibrations/Reviews following Monday
– Paper 1: Text was due before class. All
Calibrations/Reviews due this coming Monday
– Paper 2 (if we finished Chapter 8): Due Monday before
class.
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Holes, No Math Topic 4: Nuclear Physics & Chemistry
Prep for Next Time – P11
• Reading:
– BBBHNM 9
• Reading questions:
– Chapter 9 or the recommended reading
• End-of-Chapter Quizzes:
– If we finished Chapter 8, end-ofchapter quiz due before next class
(else just 7)
• Paper:
– If you see problems with the grading
of your Paper 1 send us email
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–
Work
on
revision
if
needed
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Was due Today – L13
• Reading:
– (BBBHNM Unit 2)
• Pre-Lecture Reading Questions:
– Let us know if you were misgraded
– Unit 1 Revision grades posted in eCampus
• End-of-Chapter Quizzes:
– (Chapter 7a & 7b quizzes)
• Papers:
– Paper 1, Stage 2: due before class
– Paper 2: Will be assigned today
• Honors Paper:
– Stage 1 due October 19th before class
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Prep for Next Time – P12
• Reading:
– BBBHNM 9
• Reading questions:
– Chapter 9 or the recommended reading
• End-of-Chapter Quizzes:
– If we finished Chapter 8, end-of-chapter
quiz due before next class (else just 7)
• Paper:
– If you see problems with the grading of your
Paper 1 send us email
– Work on revision if needed
– Start working on paper 2
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Prep for Today (Is now due) – L11
• Reading:
–BBBHNM 8
• End-of-Chapter Quizzes:
– Chapters 2-6
• Reading questions:
–Two questions from Chapter 8 or
recommended reading
• Paper 1:
–CPR work was due today
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Prep for Today (Is now due) – L12
• Reading:
–BBBHNM 9
• End-of-Chapter Quizzes:
– Chapter 7
• Reading questions:
–Two questions from Chapter 9
• Paper 1:
–Working on Revisions if necessary
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Paper 0 Notes
• If you believe you were misgraded on Paper 0
let us know ASAP
• If you did not pass all the pieces of Paper 0
you need to do a full revision in CPR including
calibrations and grading
– If you did well on the text, you don’t need
to change much
• Pass/Revise Grading will be posted on eCampus
after we have responded to all the requests
for regrades
• You need a passing grade on paper 0 to pass
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Sad Truth
• Every semester we have people
who don’t listen to what is said
in class and just look at their
score on CPR and decide they
have passed.
• Your score will be on eCampus.
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Protons and Neutrons
• A carbon atom
has 6 protons
(blue) and 6
neutrons (grey)
• VERY tightly
packed
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Review of a Helium Atom
Again look at the
stuff as we
zoom in
http://bigbang.physics.tamu.edu/Figures/StolenAnimations/Animation_Atom.mpg
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Exciting Atoms
Atom in
Excited State
Atom in
Ground State
Proton
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Excited Atoms Emit Light
Atom in
Ground State
Atom in
Excited State
Photon with
a specific
energy
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Analyzing Absorption Spectra
• Each element produces a specific set of
absorption (and emission) lines
• Comparing the relative strengths of these sets
of lines, we can study the composition of stars
See only
spectral
lines for
known
atoms
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Paper Notes
• ~600 words (This is the
equivalent of both side of a
sheet of paper, double spaced)
• No citations! Use your own
words
• Text should be professional. You
are “trusted guide” not a
“buddy”
or
“comedian”
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A “moving” Spectral Line…
More Red
More Blue
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Light from the Stars
A light bulb (or a star) will emit light at all
wavelengths and thus produce a continuous
spectrum
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What about the Gas Outside a Star?
• What will we see if we look at
the Gas outside the star?
• Light from the star will hit the
gas, and we see the light from
the gas itself
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The light from excited atoms
If the light hits a bunch of low speed atoms
(typically call this a gas) at specific
wavelengths it can create an emission spectrum
Light excites electrons in
atoms to higher energy states
Transition back to lower states
emits light at specific energies (wavelengths)
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When atoms “get in the way”
If a continuous spectrum of light passes through
atoms, it can create an absorption spectrum
Light excites electrons in atoms
to higher energy states
Wavelengths corresponding to the
transition energies are absorbed
from thePhysics
continuous
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The Spectra of Stars
Inner parts of a star
produces a continuous
spectrum
Outer parts absorb light at specific wavelengths
The light spectrum shows spectral lines!
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Papers for the Course
• There will be three papers for the
course
– http://faculty.physics.tamu.edu/toba
ck/109/WritingAssignments/
• Due dates are posted there
• Paper 1 will be assigned after we start
Chapter 9, due one week after we
finish Chapter 9
• You should start thinking about your
research
paperPhysics
topic
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Creating Stable Helium
Helium3
Helium3 + Helium3  Helium4 + 2 Protons
Nuclear
Reaction
Proton
Helium4
Helium3
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Writing Assignments
1. Short Assignment 1 is Due Wednesday
March 4th before the beginning of Class
• Instructions on how to turn it in are on
the web
2. Short Assignment 2 is posted
• Currently Due Wed March 25
3. Research Paper is posted
• Stage 0 due March 30th
• Stage 1 due April 13th
• Final paper due the last day of class,
May 4th
Need to be finishing Unit 2 WebCT stuff
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Making Molecules
• H20 picture from Giancoli
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• How atoms combine to form
molecules?
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Chemistry
• How do we make up the different
kinds of atoms
• Different number of protons and
neutrons in the nucleus and
electrons
• Energy states
• Quantum mechanics
• Spectral lines.
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BHOT 11 cont…
• Gravity continued… We think of gravity being caused
by the exchange of virtual gravitons (not yet
confirmed).
• Gravity is the weakest of the forces by a lot
• Two important things to know:
– It acts even at long distances
– It is (as far as we know) always attractive
• So what, if objects are really far away we might
never notice gravity, but if they are really HEAVY
then the attraction can be big.
• Earth going around the Sun.
• Others tend to cancel out.
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Uncertainty Principle
• Uncertainty Principle
determines the size of an atom
and a nucleus
• DPDX > h
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More so what…
• One more particle that we need to talk about, and that’s a
photon (“gamma ray”).
• A photon is actually light (a gamma ray hits our eyes and
that’s how we “see”)
• It also turns out that photons also play an important role in
atoms
• Why do the electrons “orbit” the nucleus?
• The protons have positive charge, the neutrons are neutral,
and the electrons are negatively charge.
• Since positive and negative charges attract each other, the
electrons are attracted to the nucleus and that’s what keeps
them “in orbit”
– Again, the truth is MUCH more complicated than this, but
its actually a good understanding…
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How do the particles talk to
each other? Feynman Diagrams
e
d
W
u


e
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Chemistry
• We can put
nucleons
together in lots
of different
ways…
• Each different
way corresponds
to a different
type of atom
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Quantum Mechanics
• Some quick discussions of quantum mechanics
(particles and waves, probability, small sizes and big
energies) and
• What do we do for Quantum mechanics
– QM and Gribbins' book?
– The great experiments? Two slit? Bohr model?
Heated metal?
– Also mention to special relativity, general
relativity, thermodynamics as applied to stars and
blackbody radiation, quantum mechanics, and any
other general scientific ideas? Later perhaps?
– Need QM for now?
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SHU 6
• Anti-matter here? Page 149
• When matter and anti-matter meet they annihilate
and disappear in a burst of energy
• How could all the matter in the universe exist and
be easily detectible if theoretically there should be
just as much antimatter around? Either the matter
and antimatter should have annihilated each other,
or we ought to be able to detect as much
antimatter in the universe, which we clearly do not.
• Evidence for anti-electrons (positrons) in 1932.
• Ends on page 153
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Questions…
• How large are electrons and
quarks?
– We don’t know… that’s what I
(and others) do for a living…
• What are they “made of”? Are
they made of anything?
Strings?
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Fundamental Building Blocks
• This is a lecture on the
fundamental building blocks of
nature…
• Need a textbook for this…
• Charm of Strange Quarks???
• Where is my lecture from
Physics 101?
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BHOT 11 cont…
• Force 2: Electromagnetic force
• Most people know about this also, it is
what causes the interactions between
electrically charge particles that we
know and love
• Electrons and protons
• Electrons and quarks
• Ignores electrically neutral particles
such as neutrons and neutrinos.
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In Class Quiz
Answer the following
question:
Why do we believe that
stars are made of atoms?
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Looking Forward
With an understanding of how to build up
nucleons, nuclei, atoms, molecules and
matter here on earth we begin to have
confidence that we can understand how
to build up planets and moons, stars
and galaxies in the sky
If we can understand how the objects in
the universe were formed we have a
chance to understand where it all came
from
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Yet more remarkable
• Want to explain WHY most of the
universe is Hydrogen
• Its not crazy to think that the
reason its mostly hydrogen is
because it started out as mostly
quarks and just turned into
Hydrogen, and not much else
because its HARD to form the
other stuff
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Why Do Stars Shine?
•Stars are Hydrogen
balls
•During the reactions
of the Hydrogen
(protons) creating
heavier elements
some of the light
escapes
•This is why stars
shine
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Different Types of Nuclei
• How do we CREATE
different types of nuclei in
nature?
• Collisions between nuclei
allow them to combine
• Decay of nuclei allow them
to change
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• Video here of photon coming in and
exciting an atom then de-exciting…
This explains excitations and then
spectral lines.
• Prism of light coming from Page 54
of BHOT
• Jonathan!
• Feynman diagram on page 71 of
BHOT.
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History
• 1816: Spectral lines: von
Fraunhofer
• Different lines from different
atoms
• 1880 Huggins: Spectral lines
indicate what the chemical
elements are
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Chemistry
• How do we make up the different
kinds of atoms
• Different number of protons and
neutrons in the nucleus and
electrons
• Energy states
• Quantum mechanics
• Spectral lines.
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Fundamental continued
• It turns out there are lots of different
types of nuclei
– This is the domain of nuclear physics
• It turns out that a nucleus is actually just a
collection of protons and neutrons
– Hydrogen: a single proton
– Helium: 2 protons and 2 neutrons
– Sodium: XX protons and XX neutrons
– More on what holds all this together
later…
– More on what protons and neutrons are
made of later (answer for now… quarks)
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Moving towards the fundamental
building blocks
• What is gas made of?
– It turns out its made of molecules of
different types
– CN, others?
• What are molecules made of?
– It turns out molecules are made of
different types of atoms put
together in different ways
– Hydrogen, Helium, Sodium, Carbon,
Nitrogen etc…
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Spectral lines and Stars
• Atoms have excited states…
these photons from the surface
of the star excites the atom
and is absorbed.
• Ok… they’re re-emitted later
when the atom de-excites, but
that goes in a random direction
so we don’t see it.
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Summary
• Given enough nucleons and
time you can eventually
make helium
• Lots of energy released in
the creation process
• From Helium and more
protons you can make even
heavier things…
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Forming Protons
Quark
qqq  Proton
Nuclear
Reaction
Quark
Proton
Quark
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• The same force holds the
nucleons together
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How Atoms Combine
• Need this?
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Electron Orbits
• Electron orbits in the electron cloud are
restricted to very specific radii and energies.
r3, E3
r2, E2
r1, E1
• These characteristic electron energies are
different
for each
individual
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Spectral Lines
• Shine white light on a bunch of
atoms:
• Prism shows the colors in white
light going in
• After going through the atoms we
are left with spectral lines
– The excited states absorb and
then re-emit in some different
direction
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• Note about this video: They
change the colors for the last
slide!!!
• And the colors are screwed up
for Helium on the last slide
also!
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