big bang, black holes, no math astr/phys 109 dr. david toback lecture 25 & 26

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ASTR/PHYS 109
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Reading:
Papers:
Paper 5 due one week after we finish Chapter 20
NOT the last day of class
Big Bang, Black Holes, No Math
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"Department of Physics On-Line Course Evaluation System“
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Before the first millionth of a second
and the
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Inflation
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Summarizing the Data so Far
Redshifts of Galaxies gives us the speed of expansion fairly accurately
The measured mass of the “stars and stuff” gives about 4% of the critical density
The Cosmic Background Radiation is consistent with a density of 100% of the critical density
Something is inconsistent…
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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
Next time
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The Rotation of Galaxies
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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
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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”
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Watch the way stars rotate around the center of Galaxies
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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
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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
Early Times & Fate of The Universe Topic 2: Dark Matter
The Data
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Simulation without
Dark Matter
http://bigbang.physics.tamu.edu/Figures/StolenAnimations/galrot_anim.gif
Watch how fast a star rotates around the center of the galaxy…
Data looks like this
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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”
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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
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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 of the Sun can bend the path of light
Result: The apparent position of a star “moved” as the light passed from outer space, past the Sun, and to us
Light’s path in curved
space time
Is here
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Galaxy
Looks like a Galaxy behind a cloud of hydrogen
Looks like a Galaxy behind a cloud of heavy “stuff” that isn’t just stars and hydrogen
Another Galaxy
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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
Prism
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More on Lensing
Sometimes we can even see more than one image of the same galaxy!
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Atoms
Dark Matter
Atoms in the Galaxies interact and slow down as they pass through each other
Dark Matter doesn’t interact much so it isn’t slowed down much
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Atoms and
Dark Matter
Atoms and
Dark Matter
The atom part and the Dark Matter part of Galaxies interact differently as they pass through each other
Atoms
Atoms
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Colliding Clusters of Galaxies
“Fast Dark Matter”
“Slow Atoms”
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Prep for Next Time – P25
Reading
eLearning Quiz
Papers
Paper 3 revisions due Tuesday at noon if you want
Paper 4 due Wednesday at 11:55PM
Prep for Next Time – P26
Reading
eLearning Quiz
Papers
Paper 5 due one week after we finish Chapter 20
NOT the last day of class
Full set of Readings So Far
Required:
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
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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
Supersymmetry
BBBHNM: Chaps. 18-22
SHU: 8 (159-164)
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
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
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Papers
All grades fixed, revision paper grades posted
Paper 3:
Still mis-graded? Let us know!
Do CPR if you submitted a revision
Paper 4:
Paper 5 (last paper, no final)
Assigned after we start Chap 20
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Other Stuff
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
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BBBHNM: Chaps. 18-22
SHU: 8 (159-164)
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
TOE: Chaps. 1-3
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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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Short Assignments 1, 2 & 3
Re-do’s are still possible. Want to revise again? Talk to me
eLearning:
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Due last day of class
If you did the Black Hole paper your paper is posted now, on Dark Matter
If you did not do the Black Hole paper you must turn in a Research Paper
Turn in at eLearning like usual
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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
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http://bigbang.physics.tamu.edu/Figures/StolenAnimations/galrot_anim.gif
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Is the universe made up of just the known particles?
Electrons?
Protons?
Neutrons?
Neutrinos?
The Earth doesn’t shine…
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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
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Does this work for Stars?
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Does this work for Stars?
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Path
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Shockwave video comparing galaxy rotation with and without 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.
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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
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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
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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”
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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”
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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
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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
The way stars rotate around the center of Galaxies
Look at the gravitational impact on light that travels through the Universe towards us
Colliding Galaxies
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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
Other Mass/Energy in the Universe (This Time)
Inflation (Coming Soon)
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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
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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…
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Nature of baryonic dark matter still very uncertain and speculative.
Baryonic Dark Matter
One component: MAssive Compact Halo Objects = “MACHOs”:
Small compact objects (e.g., brown dwarfs, small black holes) acting as gravitational lenses.
Earth
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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?
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big bang, black holes, no math astr/phys 109 dr. david toback lecture 25 & 26

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