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Big Bang, Black
Holes, No Math
ASTR/PHYS 109
Dr. David Toback
Lecture 25 & 26
Big Bang, Black Early Times & Fate of The Universe
Holes, No Math
Topic 2: Dark Matter
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Prep for Today (Is now due) – L26
• Reading:
– Required: BBBHNM: Chapter 20
• eLearning Quizzes:
– Chapters 2-18
• Reading questions:
– Two questions from Chapter 20
• Papers:
– Paper 4 CPR due Wednesday at Noon
– Paper 5 due one week after we finish
Chapter 20
• NOT the last day of class
Big
Early Times & Fate of The Universe
2 Bang, Black
Holes, No Math
Topic 2: Dark Matter
Course Evaluations
This semester course evaluations
will be done online
"Department of Physics On-Line
Course Evaluation System“
http://evaluation.tamu.edu/
Please, take a few minutes to fill
these out. I really appreciate
it!
3
Big
Bang, Black Early Times & Fate of The Universe
Holes, No Math
Topic 2: Dark Matter
Unit 6
Going back in time and going
forward in time
Before the first millionth of
a second
and the
Fate of the Universe
Big Bang, Black Early Times & Fate of The Universe
Holes, No Math
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Outline of Unit 6
1.Possible Fates of the
Universe
Today
2.The Case for Dark Matter
3.Particle Physics and Dark
Matter
4.Inflation
5.Dark
Big Bang, Black Energy
Early Times & Fate of The Universe
5
Holes, No Math
Topic 2: Dark Matter
Summarizing the Data so Far
1. Redshifts of Galaxies gives us the
speed of expansion fairly accurately
2. The measured mass of the “stars and
stuff” gives about 4% of the critical
density
3. The Cosmic Background Radiation is
consistent with a density of 100% of
the critical density
Something is inconsistent…
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Holes, No Math
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The Story
There is a strong case to be made
that there is Matter and Energy in
the Universe we can’t “see” directly
• The Evidence for Dark Matter
– Today
• Particle Physics and Dark Matter
– The Standard Model and
Supersymmetry
– Next time
Big Bang, Black Early Times & Fate of The Universe
Holes, No Math
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Today’s Lecture
The Case for Dark Matter
1.The Rotation of Galaxies
2.Gravitational Lensing
3.Colliding Galaxies
Big Bang, Black Early Times & Fate of The Universe
Holes, No Math
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What is Dark Matter and why do we
call it Dark Matter?
What do we see when we
look at the Heavens?
• Our eyes see photons,
but with other
detectors we can see
electrons, protons,
atoms and neutrinos
• All these things interact
with photons  we can
“see” them because
they produce the light
we observe
Big Bang, Black Early Times & Fate of The Universe
Holes, No Math
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Dark Matter
• If there is something else
out there it must not
interact with light very
much
• Call this “Dark Matter”
Big Bang, Black Early Times & Fate of The Universe
Holes, No Math
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Evidence 1
Watch the way
stars rotate around
the center of
Galaxies
Big Bang, Black Early Times & Fate of The Universe
Holes, No Math
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The Planets and the Sun
General Relativity does
a good job of
predicting the planets
path around the sun
assuming virtually all
the mass of the Solar
system is located at
the Sun
– Only small influence
due to the small
masses of the
other planets
Big Bang, Black Early Times & Fate of The Universe
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What about Stars and Galaxies?
• Can again use General Relativity to
predict the orbits of stars as they
move around the galaxy
• Should look like a complex collection
of individual stars all in separate
free orbits around the heart of the
galaxy
• Problem: This isn’t what the data
shows
Big Bang, Black Early Times & Fate of The Universe
Holes, No Math
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The Data
Big Bang, Black Early Times & Fate of The Universe
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Does this work for Stars?
Watch how fast a star rotates around the
center of the galaxy…
Simulation without
Dark Matter
Simulation with lots of
Dark Matter particles in
the galaxy
Big Bang, Black Early Times & FateData
of The
Universe
looks
like this
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Holes,
No Math
http://bigbang.physics.tamu.edu/Figures/StolenAnimations/galrot_anim.gif
Topic 2: Dark Matter
Stuff Outside the Stars?
• Can also look at the clouds of
hydrogen on the outskirts of the
galaxy
• Also rotating faster than they
should be
• Looks like they are feeling the
gravity of a large amount of
mass we can’t “see”
Big Bang, Black Early Times & Fate of The Universe
Holes, No Math
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Dark Matter?
Data well explained
by lots of “Dark
Matter” we can’t
see
Mostly clumped at
the center due to
gravity
Lots of it in a
“halo” around the
entire galaxy
Big Bang, Black Early Times & Fate of The Universe
Holes, No Math
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Evidence 2
Look at the
gravitational impact on
light that travels
through the Universe
towards us
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General Relativity and Light
• The large mass
Is here
“Looks” like
of the Sun can
its here
bend the path
of light
• Result: The
apparent
position of a
Light’s path in
star “moved” as
curved
the light passed
space time
from outer
space, past the
Big
Bang, and
Black Early
Times & Fate of The Universe
Sun,
to
us
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Holes, No Math
Topic 2: Dark Matter
Looking at Light from the Universe
Galaxy
Light from a Galaxy
Hydrogen
Another
Galaxy
Cloud
Looks like a Galaxy
Looks
Lookslike
likea aGalaxy
Galaxy
behind a cloud of heavy
behind a cloud of
“stuff” that isn’t just
hydrogen
stars and hydrogen
Big Bang, Black Early Times & Fate of The Universe
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Lensing of Galaxies
Prism
• Dark Matter
“Lenses” the
galaxies behind
them like a
prism
• Evidence that
the light coming
to us is passing
through lots of
matter we can’t
see directly
Big Bang, Black Early Times & Fate of The Universe
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More on Lensing
Sometimes
we can
even see
more
than one
image of
the same
galaxy!
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Evidence 3
Colliding
Clusters of
Galaxies
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Look at Colliding Clusters of
Galaxies
Atoms in the Galaxies interact and slow down as
they pass through each other
Atoms
Atoms
Dark Matter doesn’t interact much so it isn’t
slowed down much
Dark Matter
Dark Matter
Big Bang, Black Early Times & Fate of The Universe
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Colliding Galaxy Clusters
The atom part and the Dark Matter
part of Galaxies interact differently
as they pass through each other
Atoms and
Dark Matter
Atoms and
Dark Matter
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Colliding Galaxy Clusters
Galaxy
Galaxy
Galaxy
Light from a Galaxy
Atoms and
Dark Matter
Atoms and
Dark Matter
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Evidence for This in Nature?
Colliding Clusters of Galaxies
Blue is the part from
lensing only
“Fast  Dark Matter”
Red part from
observing the light
“Slow Atoms”
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http://bigbang.physics.tamu.edu/Figures/StolenAnimations/bullett_anim_lg.mpg
Big Bang, Black Early Times & Fate of The Universe
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What IS Dark
Matter?
We don’t know…
Still working on it…
Big Bang, Black Early Times & Fate of The Universe
Holes, No Math
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Prep for Next Time – P25
• Reading
– Required: BBBHNM Chapter 20
• Reading questions
– Two questions from Chapter 20
• eLearning Quiz
– If we finished Chapter 19 then end-ofchapter quiz 19
• Papers
– Paper 3 revisions due Tuesday at noon if
you want
– Paper 4 due Wednesday at 11:55PM
Big Bang, Black Early Times & Fate of The Universe
Holes, No Math
Topic 2: Dark Matter
Prep for Next Time – P26
• Reading
– Required: BBBHNM Chapter 20
• Reading questions
– Two questions from Chapter 20
• eLearning Quiz
– If we finished Chapter 19 then end-ofchapter quiz 19
• Papers
– Paper 4 CPR due Wednesday at Noon
– Paper 5 due one week after we finish
Chapter 20
Big Bang,
Black the
Earlylast
Times
& Fate
The Universe
• NOT
day
of ofclass
Holes, No Math
Topic 2: Dark Matter
Full set of Readings So Far
• Required:
– BBBHNM: Chaps. 1-20
• Recommended:
– TFTM: Chaps. 1-5
– BHOT: Chaps. 1-7, 8 (68-76), 9 and
11 (117-137), 12
– SHU: Chaps. 1-3, 4(77-86), 5(95114), 6-8 (up-to-page 164)
– TOE: Chaps. 1-3
– Seeds (Cosmology in the 21st Century)
Big Bang, Black Early Times & Fate of The Universe
Holes, No Math
Topic 2: Dark Matter
Big Bang, Black Early Times & Fate of The Universe
Holes, No Math
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http://bigbang.physics.tamu.edu/Figures/StolenAnimations/dark_matter_lg.mpg
Big Bang, Black Early Times & Fate of The Universe
Holes, No Math
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For Next Time
Could the Dark Matter just be a bunch of a single type of new fundamental
particle?
• Chap 20: Particle Physics
– The Standard Model of Particle Physics
– Supersymmetry
Full reading for Unit 6:
• BBBHNM: Chaps. 18-22
• SHU: 8 (159-164)
• BHOT: 11 (122-137), 12
• Seeds (Cosmology in the 21st Century, Web Handout)
Full reading through Unit 6:
• BBBHNM: Chaps. 1-22
• TFTM: Chaps. 1-5
• BHOT: Chaps. 1-7, 8 (68-76), 9 and 11 (117-137), 12
• SHU: Chaps. 1-3, 4(77-86), 5(95-114), 6-8 (up-to-page 164)
• TOE: Chaps. 1-3
• Seeds (Cosmology in the 21st Century)
Lecture prep: Turn in on eLearning
Two questions from Chapter 20 you want to know the answer to
Big Bang, Black Early Times & Fate of The Universe
Holes, No Math
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The Data
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Papers
• Paper 1 is done
• Paper 2 grades are on eLearning
– All grades fixed, revision paper grades posted
• Paper 3:
– We have fixed papers for calibration problems
– Still mis-graded? Let us know!
– Do CPR if you submitted a revision
• Paper 4:
– Was due today before class
• Paper 5 (last paper, no final)
– Assigned after we start Chap 20
Big
Early Times & Fate of The Universe
37 Bang, Black
Holes, No Math
Topic 2: Dark Matter
Other Stuff
• Elearning:
– Unit 5 has Unit 6 questions (sigh…)
– 5 and 6 will both be due last day of class
• Schedule from here on out
– Today: Ch 19 & 20 (paper 4 due)
– Wed Apr 21: No class, Muster
– Mon Apr 26: Ch 20 &21 (paper 4 CPR due)
– Wed Apr 28: Ch 21 & 22
– Mon May 3: Ch 22 (last day of class,
paper 5 due)
Big Bang, Black Early Times & Fate of The Universe
Holes, No Math
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The Reading for Unit 6
Full reading for Unit 6:
• BBBHNM: Chaps. 18-22
• SHU: 8 (159-164)
• BHOT: 11 (122-137), 12
• Seeds (Cosmology in the 21st Century, Web Handout)
Full reading through Unit 6:
• BBBHNM: Chaps. 1-22
• TFTM: Chaps. 1-5
• BHOT: Chaps. 1-7, 8 (68-76), 9 and 11 (117-137),
12
• SHU: Chaps. 1-3, 4(77-86), 5(95-114), 6-8 (upto-page 164)
• TOE: Chaps. 1-3
• Seeds (Cosmology in the 21st Century)
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Evolution of The Universe
Put it all together and
there is significant evidence
that there is LOTS of dark
matter in the Universe
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Writing Assignments
Short Assignments 1, 2 & 3
Re-do’s are still possible.
Want to revise again? Talk to
me
eLearning:
Unit 5 past due
Need to be working on Unit 6
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Holes, No Math
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Last Paper
Due last day of class
1. If you did the Black Hole paper
your paper is posted now, on
Dark Matter
2. If you did not do the Black Hole
paper you must turn in a
Research Paper
Turn in at eLearning like usual
Big Bang, Black Early Times & Fate of The Universe
Holes, No Math
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Ok… What Does it Look Like?
• Stars look more like they are
turning as if they are part of a
single solid, giant wheel
• Looks like this wheel would be
MUCH more massive than the
sum of all the stars in the
galaxy
• Also, much more spread out than
most of the mass at the center
Big Bang, Black Early Times & Fate of The Universe
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Does this work for Stars?
Watch how fast a star rotates around the
center of the galaxy…
http://bigbang.physics.tamu.edu/Figures/StolenAnimations/galrot_anim.gif
Big Bang, Black Early Times & Fate of The Universe
Holes, No Math
Topic 2: Dark Matter
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Evidence 4
• Is the universe made up of just the
known particles?
– Electrons?
– Protons?
– Neutrons?
– Neutrinos?
• Perhaps its just known particles we
can’t see?
– The Earth doesn’t shine…
Big Bang, Black Early Times & Fate of The Universe
Holes, No Math
Topic 2: Dark Matter
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Composed of Normal Matter?
• Lots of “protons and
neutrons” we can’t see?
• Look at the amount of
Deuterium and Lithium in
the Universe
• The data predict that
normal matter is only
~4% of the critical
density
• Consistent with other
observations
Big Bang, Black Early Times & Fate of The Universe
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Does this work for Stars?
Watch how
fast a star
rotates
around the
center of
the galaxy…
Big Bang, Black Early Times & Fate of The Universe
Holes, No Math
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Does this work for Stars?
Watch how
fast a star
rotates
around the
center of
the galaxy…
Big Bang, Black Early Times & Fate of The Universe
Holes, No Math
Topic 2: Dark Matter
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How the Earth looks to Light…
Path
doesn’t curve
Big Bang, Black Early Times & Fate of The Universe
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Topic 2: Dark Matter
Path
does curve
49
What is the Evidence for Dark Matter?
Big Bang, Black Early Times & Fate of The Universe
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• Need a picture here…
• TCP Figure 21.1, page 614 ?
• Shockwave video comparing
galaxy rotation with and without
dark matter
Big Bang, Black Early Times & Fate of The Universe
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Topic 2: Dark Matter
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Dark Matter
• Combined mass of all “visible” matter (i.e.
emitting any kind of radiation) in the universe
adds up to much less than the critical density.
• Gravitational
lensing shows
that some
clusters contain
10 times as
much mass as is
directly visible.
Big Bang, Black Early Times & Fate of The Universe
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• From this we can conclude (but not
prove) that much of our galaxy’s mass
must lie beyond the distance of the
Sun’s orbit around the galactic center,
and distributed throughout the galaxy’s
spherical halo
• Most of the light comes from the center
• Thus, there is a large amount of matter
that we can’t see
Big Bang, Black Early Times & Fate of The Universe
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Rotation Stuff
• However, there is lots of “dark
matter” that we cannot see
directly but which we know must
be there
Big Bang, Black Early Times & Fate of The Universe
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Topic 2: Dark Matter
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SHU 8 cont…
• This “dark, unseen matter must
have so much mass that it held
the stars in position, making
them the shining hub of a giant
invisible wheel”
Big Bang, Black Early Times & Fate of The Universe
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Topic 2: Dark Matter
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TCP 21
• One of our favorite reasons is to
look at the atomic hydrogen clouds
in the Milky Way.
• The clouds lay very far out from
the galactic center (further out
than our sun) and are rotating
faster than they should be if they
were just feeling the gravity of the
mass we can “see”
Big Bang, Black Early Times & Fate of The Universe
Holes, No Math
Topic 2: Dark Matter
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• There had to be part of the
galaxy which were just not
seeing, and that this must make
up far more of the total mass
of the galaxy than the stars we
could observe shining
Big Bang, Black Early Times & Fate of The Universe
Holes, No Math
Topic 2: Dark Matter
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Why do we believe?
• Why do we believe there is other
stuff out there that we can’t see?
• Three reasons
1. The way stars rotate around the
center of Galaxies
2. Look at the gravitational impact
on light that travels through the
Universe towards us
3. Colliding Galaxies
Big Bang, Black Early Times & Fate of The Universe
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Two Topics
We can use the evidence that we
live in a Flat, Homogenous and
Isotropic Universe as evidence
for two main things
1. Other Mass/Energy in the
Universe (This Time)
2. Inflation (Coming Soon)
Big Bang, Black Early Times & Fate of The Universe
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• Evidence that we live in a Flat,
Homogenous and Isotropic Universe
and its implications
• If we live in a flat Universe where
is the rest of the Mass/Energy
that makes up the rest of the
“critical Density”
• Missing Mass and Energy in the
Universe and the case for Dark
Matter
Big Bang, Black Early Times & Fate of The Universe
Holes, No Math
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Outline
• SHU 8 first part
• TCP 21, but not really…
Big Bang, Black Early Times & Fate of The Universe
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• “If you assumed that all the stars
we can see in the galaxy are free
to affect each other gravitationally
in exactly the same way gravity
governs the dynamics of the solar
system, then our galaxy should
rotate differently than we observe
them to…
Big Bang, Black Early Times & Fate of The Universe
Holes, No Math
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Big Bang, Black Early Times & Fate of The Universe
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Baryonic Dark Matter
Brightness of background star
Nature of baryonic dark matter still
very uncertain and speculative.
One component:
MAssive Compact
Halo Objects =
“MACHOs”:
Time
Small compact
objects (e.g.,
brown dwarfs,
small black
holes) acting as
gravitational
lenses.
Big Bang, Black Early Times & Fate of The Universe
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Distant
background
star
Holes, NoEarth
Math MACHO Topic 2: Dark Matter
TCP 21 cont…
• The universe has two possible fates: It
might continue to expand forever, or it
might someday stop expanding and begin
to collapse
• We don’t yet know the fate of the
universe because the answer depends on
the overall density of matter in the
universe – and we cannot determine the
overall density until we first determine
how much dark matter is out there
• Finished?
Big Bang, Black Early Times & Fate of The Universe
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Big Bang, Black Early Times & Fate of The Universe
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• This is some
text
Big Bang, Black Early Times & Fate of The Universe
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Big Bang, Black Early Times & Fate of The Universe
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• Dark unseen matter surrounding
the galaxy like a halo
Big Bang, Black Early Times & Fate of The Universe
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