1. Astronomy 305/Frontiers in Astronomy
Class web site:
Office: Darwin 329A and NASA EPO
(707)
Best way to reach me:
12/2/03
Prof. Lynn Cominsky

2. Group 14
Great job, Group 14!
12/2/03
Prof. Lynn Cominsky

3. 12/2/03
Prof. Lynn Cominsky

4. What is the Universe made of?
Regular matter
Heavy elements 0.03%
Stars 0.5%
Free Hydrogen and Helium 4% (Lecture 11)
Neutrinos 0.3% (Lecture 10)
Dark Energy 60% (Lecture 13)
Dark Matter 30% (this lecture)
You can't see it but you can feel it!
12/2/03
Prof. Lynn Cominsky

5. Kepler’s Third Law movie
P2 is proportional to a3
12/2/03
Prof. Lynn Cominsky

6. Dark Matter Evidence
In 1930, Fritz Zwicky discovered that the galaxies in the Coma cluster were moving too fast to remain bound in the cluster according to the Virial Theorem
KPNO image of the Coma cluster of galaxies - almost every object in this picture is a galaxy! Coma is 300 million light years away.
12/2/03
Prof. Lynn Cominsky

7. Virial Theorem Stable galaxies should obey this law: 2K = -U
where K=½mv2 is the Kinetic Energy
U = -aGMm/r is the Potential Energy (a is usually , and depends on the mass distribution)
Putting these together, we have M=v2r/aG.
Measure M, r and v2 from observations of the galaxies; then use M and r to calculate vvirial
Compare vmeasured to vvirial
vmeasured > vvirial which implies M was too small
12/2/03
Prof. Lynn Cominsky

8. Dark Matter Evidence
Measure the velocity of stars and gas clouds from their Doppler shifts at various distances
Velocity curve flattens out!
Halo seems to cut off after r= 50 kpc
Galaxy Rotation Curves
NGC 3198
v2=GM/r where M is mass within a radius r
Since v flattens out, M must increase with increasing r!
12/2/03
Prof. Lynn Cominsky

9. Dark Matter Evidence Cluster Mass Java simulation
Rotation Curve Java simulation
12/2/03
Prof. Lynn Cominsky

10. Dark Matter Evidence Hot gas in Galaxy Clusters
Measure the mass of light emitting matter in galaxies in the cluster (stars)
Measure mass of hot gas - it is 3-5 times greater than the mass in stars
Calculate the mass the cluster needs to hold in the hot gas - it is times more than the mass of the gas plus the mass of the stars!
Hot gas in Galaxy Clusters
12/2/03
Prof. Lynn Cominsky

11. Dark Matter Halo
The rotating disks of the spiral galaxies that we see are not stable
Dark matter halos provide enough gravitational force to hold the galaxies together
The halos also maintain the rapid velocities of the outermost stars in the galaxies
12/2/03
Prof. Lynn Cominsky

12. Types of Dark Matter
Baryonic - ordinary matter: MACHOs, white, red or brown dwarfs, planets, black holes, neutron stars, gas, and dust
Non-baryonic - neutrinos, WIMPs or other Supersymmetric particles and axions
Cold (CDM) - a form of non-baryonic dark matter with typical mass around 1 GeV/c2 (e.g., WIMPs)
Hot (HDM) - a form of non-baryonic dark matter with individual particle masses not more than eV/c2 (e.g., neutrinos)
12/2/03
Prof. Lynn Cominsky

13. Primordial Matter
Normal matter is 3/4 Hydrogen (and about 1/4 Helium) because as the Universe cooled from the Big Bang, there were 7 times as many protons as neutrons
Almost all of the Deuterium made Helium
Hydrogen = 1p + 1e
Deuterium = 1p + 1e + 1n
Helium = 2p + 2e + 2n
12/2/03
Prof. Lynn Cominsky

14. Primordial Matter
The relative amounts of H, D and He depend on h = (protons + neutrons) / photons
h is very small - We measure about 1 or 2 atoms per 10 cubic meters of space vs. 411 photons in each cubic centimeter
The measured value for h is the same or a little bit smaller than that derived from comparing relative amounts of H, D and He
Conclusion: we may be missing some of baryonic matter, but not enough to account for the observed effects from dark matter!
12/2/03
Prof. Lynn Cominsky

15. Baryonic Dark Matter Baryons are ordinary matter particles
Protons, neutrons and electrons and atoms that we cannot detect through visible radiation
Primordial Helium (and Hydrogen) – recently measured – increased total baryonic content significantly
Brown dwarfs, red dwarfs, planets
Possible primordial black holes?
Baryonic content limited by primordial Deuterium abundance measurements
12/2/03
Prof. Lynn Cominsky

16. Baryonic - Brown Dwarfs
Mass around 0.08 Mo
Do not undergo nuclear burning in cores
First brown dwarf star Gliese 229B
12/2/03
Prof. Lynn Cominsky

17. Baryonic - Red Dwarf Stars
Expected 38 red dwarfs: Seen 0!
HST searched for red dwarf stars in the halo of the Galaxy
Surprisingly few red dwarf stars were found, < 6% of mass of galaxy halo
12/2/03
Prof. Lynn Cominsky

18. Ghost Galaxies Also known as low surface brightness galaxies
Studies have shown that fainter, elliptical galaxies have a larger percentage of dark matter (up to 99%)
This leads to the surprising conclusion that there may be many more ghostly galaxies than those we can see!
Each ghost galaxy has a mass around 10 million Mo
12/2/03
Prof. Lynn Cominsky

19. Baryonic –MACHOs Massive Compact Halo Objects
Many have been discovered through gravitational micro-lensing
Not enough to account for Dark Matter
And few in the halo!
Mt. Stromlo Observatory in Australia (in better days)
12/2/03
Prof. Lynn Cominsky

20. Baryonic – MACHOs 4 events towards the LMC
45 events towards the Galactic Bulge
8 million stars observed in LMC
10 million stars observed in Galactic Bulge
27,000 images since 6/92
12/2/03
Prof. Lynn Cominsky

21. Gravitational Microlensing
Scale not large enough to form two separate images
movie
12/2/03
Prof. Lynn Cominsky

22. Baryonic – black holes
Primordial black holes would form at 10-5 s after the Big Bang from regions of high energy density
Sizes and numbers of primordial black holes are unknown
If too large, you would be able to see their effects on stars circulating in the outer Galaxy
Black holes also exist at the centers of most galaxies – but are accounted for by the luminosity of the galaxy’s central region
12/2/03
Prof. Lynn Cominsky

23. So, it must be a black hole!
Black Hole MACHO
Isolated black hole seen in Galactic Bulge
Distorts gravitational lensing light curve
Mass of distorting object can be measured
No star is seen that is bright enough…..
So, it must be a black hole!
12/2/03
Prof. Lynn Cominsky

24. Strong Gravitational Lensing
12/2/03
Prof. Lynn Cominsky

25. Strong Gravitational Lensing
HST image of background blue galaxies lensed by orange galaxies in a cluster
“Einstein’s rings” can be formed for the correct alignment
12/2/03
Prof. Lynn Cominsky

26. Large Survey Synoptic Telescope
At least 8 meter telescope
About 3 degree field of view with high angular resolution
Resolve all background galaxies and find redshifts
Goal is 3D maps of universe back to half its current age
12/2/03
Prof. Lynn Cominsky

27. Gravitational Lens Movie #1
Movie shows evolution of distortion as cluster moves past background during 500 million years
Dark matter is clumped around orange cluster galaxies
Background galaxies are white and blue
12/2/03
Prof. Lynn Cominsky

28. Gravitational Lens Movie #2
Movie shows evolution of distortion as cluster moves past background during 500 million years
Dark matter is distributed more smoothly around the cluster galaxies
Background galaxies are white and blue
12/2/03
Prof. Lynn Cominsky

29. Strong Gravitational Lensing
Spherical lens
Perfect alignment
Note formation of Einstein’s rings
movie
12/2/03
Prof. Lynn Cominsky

30. Strong Gravitational Lensing
movie
Elliptical lens
Einstein’s rings break up into arcs if you can only see the brightest parts
12/2/03
Prof. Lynn Cominsky

31. Baryonic – cold gas
We can see almost all the cold gas due to absorption of light from background objects
Gas clouds range in size from 100 pc (Giant Molecular Clouds) to Bok globules (0.1 pc)
Mass of gas is about the same as mass of stars, and is part of total baryon inventory
Gas clouds in Lagoon nebula
12/2/03
Prof. Lynn Cominsky

32. Baryonic –dust
Dust is made of elements heavier than Helium, which were previously produced by stars (<2% of total)
Dust absorbs and reradiates background light
Dust clouds of the dark Pipe nebula
12/2/03
Prof. Lynn Cominsky

33. Non-baryonic: Neutrinos
There are about 100 million neutrinos per m3
More (or less) types of neutrinos would lead to more (or less) primordial Helium than we see
Neutrinos with mass affect the formation of structure in the Universe
Much less small scale structure would be present
Observed structure sets limits on how much mass neutrinos may have, and on their contribution to dark matter.
The sum of all the mn ~ 5 h502 eV (due to models of Hot and Cold DM)
12/2/03
Prof. Lynn Cominsky

34. Non-baryonic - axions
Extremely light particles, with typical mass of 10-6 eV/c2
Interactions are 1012 weaker than ordinary weak interaction
Density would be 108 per cubic centimeter
Velocities are low
Axions may be detected when they convert to low energy photons after passing through a strong magnetic field
12/2/03
Prof. Lynn Cominsky

35. Searching for axions
Superconducting magnet to convert axions into microwave photons
Cryogenically cooled microwave resonance chamber
Cavity can be tuned to different frequencies
Microwave signal amplified if seen
12/2/03
Prof. Lynn Cominsky

36. Non-baryonic - WIMPs Weakly Interacting Massive Particles
Predicted by Supersymmetry (SUSY) theories of particle physics
Supersymmetry tries to unify the four forces of physics by adding extra dimensions
WIMPs would have been easily detected in acclerators if M < 15 GeV/c2
The lightest WIMPs would be stable, and could still exist in the Universe, contributing most if not all of the Dark Matter
12/2/03
Prof. Lynn Cominsky

37. CDMS Lab 35 feet under Stanford
CDMS for WIMPs
Cryogenic Dark Matter Search
6.4 million events studied - 13 possible candidates for WIMPs
All are consistent with expected neutron flux
Cryostat holds T= 0.01 K
CDMS Lab 35 feet under Stanford
12/2/03
Prof. Lynn Cominsky

38. Detecting WIMPs?
Laboratory experiments - DAMA experiment 1400 m underground at Gran Sasso Laboratory in Italy announced the discovery of seasonal modulation evidence for 52 GeV WIMPs
100 kg of Sodium Iodide, operated for 4 years
CDMS has 0.5 kg of Germanium, operated for 1 year, but claims better
background rejection techniques
12/2/03
Prof. Lynn Cominsky

39. HDM vs. CDM models
Supercomputer models of the evolution of the Universe show distinct differences
Rapid motion of HDM particles washes out small scale structure – the Universe would form from the “top down”
CDM particles don’t move very fast and clump to form small structures first – “bottom up”
CDM
HDM
12/2/03
Prof. Lynn Cominsky

40. Largest structures are now just forming
CDM models vs. density
CDM models as a function of z (look-back time)
Largest structures are now just forming
Now
Z=0.5
Z=1.0
Critical density
Low density
12/2/03
Prof. Lynn Cominsky

41. Dark Matter Activity
You will search a paper plate “galaxy” for some hidden mass by observing its effect on how the “galaxy” “rotates”
In order to balance, the torques on both sides must be equal:
T1 = F1X1 = F2X2 = T2
where
F1 = m1g and
F2 = m2g
12/2/03
Prof. Lynn Cominsky

42. Superstrings
Strings are little closed loops that are 1020 times smaller than a proton
Strings vibrate at different frequencies
Each resonant vibration frequency creates a different particle
Matter is composed of harmonies from vibrating strings – the Universe is a string symphony
“String theory is twenty-first century physics that fell accidentally into the twentieth century” - Edward Witten
12/2/03
Prof. Lynn Cominsky

43. Superstrings
Strings can execute many different motions through spacetime
But, there are only certain sets of motions that are self-consistent
Gravity is a natural consequence of a self-consistent string theory – it is not something that is added on later
Self-consistent string theories only exist in 10 or 26 dimensions – enough mathematical space to create all the particles and interactions that we have observed
12/2/03
Prof. Lynn Cominsky

44. Superstring Dimensions
Since we can observe only 3 spatial and 1 time dimensions, the extra 6 dimensions (in a 10D string theory) are curled up to a very small size
The shape of the curled up dimensions is known mathematically as a Calabi-Yau space
12/2/03
Prof. Lynn Cominsky

45. Superstring Universe
At each point in 3D space, the extra dimensions exist in unobservably small Calabi-Yau shapes
12/2/03
Prof. Lynn Cominsky

46. Superstring Theories
There are at least five different versions of string theory, which seem to have different properties
As physicists began to understand the mathematics, the different versions of the theories began to resemble each other (“duality”)
In 1995, Edward Witten showed how all five versions were really different mathematical representations of the same underlying theory
This new theory is known as M-theory (for Mother or Membrane)
12/2/03
Prof. Lynn Cominsky

47. M-Theory
Unification of five different types of superstring theory into one theory called M-theory
M-theory has 11 dimensions
12/2/03
Prof. Lynn Cominsky

48. Some questions
Can we find the underlying physical principles which have led to us to string theory?
Does the correct string (or membrane) theory have 10 or 11 dimensions?
Will we ever be able to find evidence for the curled up dimensions?
Is string theory really the long-sought “Theory of Everything”?
Will any non-physicists ever be able to understand string theory?
Hear and see Brian Greene in NOVA’s “Elegant Universe”
12/2/03
Prof. Lynn Cominsky

49. Web Resources
VROOM visualization of 4 dimensions ndin.html
Ned Wright’s Cosmology Tutorial
Fourth dimension web site
12/2/03
Prof. Lynn Cominsky

50. Web Resources Michio Kaku’s web site http://www.mkaku.org
E. Lowry’s EM Field in Spacetime
Visualizing tensor fields tanfordTensorFieldVis/CGA93/abstract.html
Exploring the Shape of Space
12/2/03
Prof. Lynn Cominsky

51. Web Resources
Astronomy picture of the Day
Imagine the Universe
Center for Particle Astrophysics
Dark Matter telescope
Dark Matter Activity # ark_matter.html
12/2/03
Prof. Lynn Cominsky

52. Web Resources
Jonathan Dursi’s Dark Matter Tutorials & Java applets
MACHO project
National Center for Supercomputing Applications
Pete Newbury’s Gravitational Lens movies
12/2/03
Prof. Lynn Cominsky

53. Web Resources
Alex Gary Markowitz’ Dark Matter Tutorial
Martin White’s Dark Matter Models
Livermore Laboratory axion search
Dark Matter Activity #1
12/2/03
Prof. Lynn Cominsky