march 25, 2003lynn cominsky - cosmology a3501 professor lynn cominsky department of physics and...
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March 25, 2003 Lynn Cominsky - Cosmology A350
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Professor Lynn Cominsky
Department of Physics and Astronomy
Offices: Darwin 329A and NASA EPO
(707) 664-2655
Best way to reach me: lynnc@charmian.sonoma.edu
Astronomy 350Cosmology
March 25, 2003 Lynn Cominsky - Cosmology A350
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Group 8
Robert Angeli Jacy Maka Ryan McDaniel Rena Morabe
March 25, 2003 Lynn Cominsky - Cosmology A350
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Composition of the Cosmos
March 25, 2003 Lynn Cominsky - Cosmology A350
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Kepler’s Third Law movieP2 is proportional to a3
March 25, 2003 Lynn Cominsky - Cosmology A350
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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.
March 25, 2003 Lynn Cominsky - Cosmology A350
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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 0.5 - 2, 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
March 25, 2003 Lynn Cominsky - Cosmology A350
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Galaxy Rotation Curves 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
NGC 3198
v2=GM/r where M is mass within a radius r
Since v flattens out, M must increase with increasing r!
March 25, 2003 Lynn Cominsky - Cosmology A350
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Dark Matter Activity #1
Measure the radial velocity as a function of distance from the center of the galaxy
Calculate the mass of the galaxy at a given distance from the center, for each radial velocity
Measure the light coming from the galaxy inside of a given radius
Calculate the mass of the galaxy again, from the light that it emits at a given distance from the center
Plot the masses (from the radial velocity) vs. the masses (from the light)
Answer the other questions on the worksheet
March 25, 2003 Lynn Cominsky - Cosmology A350
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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 5 - 10 times more than the mass of the gas plus the mass of the stars!
March 25, 2003 Lynn Cominsky - Cosmology A350
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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
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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 10-100 eV/c2 (e.g., neutrinos)
March 25, 2003 Lynn Cominsky - Cosmology A350
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Big Bang
Written, directed and starring the Physics Chanteuse Lynda Williams
From her CD Cosmic Cabaret Available from www.scientainment.com
March 25, 2003 Lynn Cominsky - Cosmology A350
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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
March 25, 2003 Lynn Cominsky - Cosmology A350
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Primordial Matter
The relative amounts of H, D and He depend on = (protons + neutrons) / photons
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 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!
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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
March 25, 2003 Lynn Cominsky - Cosmology A350
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Baryonic - Brown DwarfsMass around 0.08 Mo
Do not undergo nuclear burning in cores
First brown dwarf star Gliese 229B
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Baryonic - Red Dwarf Stars
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
Expected 38 red dwarfs: Seen 0!
March 25, 2003 Lynn Cominsky - Cosmology A350
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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
March 25, 2003 Lynn Cominsky - Cosmology A350
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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)
March 25, 2003 Lynn Cominsky - Cosmology A350
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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
March 25, 2003 Lynn Cominsky - Cosmology A350
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Gravitational Microlensing
Scale not large enough to form two separate images
movie
March 25, 2003 Lynn Cominsky - Cosmology A350
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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
March 25, 2003 Lynn Cominsky - Cosmology A350
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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…..
March 25, 2003 Lynn Cominsky - Cosmology A350
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Strong Gravitational Lensing
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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
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Strong Gravitational Lensing
Spherical lens Perfect alignment Note formation of
Einstein’s rings
movie
March 25, 2003 Lynn Cominsky - Cosmology A350
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Strong Gravitational Lensing
Elliptical lens Einstein’s rings
break up into arcs if you can only see the brightest parts
movie
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Dark Matter 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
March 25, 2003 Lynn Cominsky - Cosmology A350
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Gravitational Lens Movie #1
Dark matter is clumped around orange cluster galaxies
Background galaxies are white and blue
Movie shows evolution of distortion as cluster moves past background during 500 million years
March 25, 2003 Lynn Cominsky - Cosmology A350
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Gravitational Lens Movie #2
Dark matter is distributed more smoothly around the cluster galaxies
Background galaxies are white and blue
Movie shows evolution of distortion as cluster moves past background during 500 million years
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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
March 25, 2003 Lynn Cominsky - Cosmology A350
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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
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Non-baryonic - neutrinos
Start with a decaying neutron at rest This reaction does not conserve energy because the
proton and electron together do not weigh as much as the neutron
The reaction also does not conserve momentum, as nothing is moving to the left
The anti-neutrino makes it all balanceproton
electronneutronanti-electron
neutrino
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Neutrino mysteries
Neutrinos are believed to have zero mass and therefore can travel at the speed of light
Neutrinos interact very weakly with other particles
There are about 100 million neutrinos per cubic meter
There are three types of neutrinos (and anti-neutrinos): electron, muon and tau
More (or less) types of neutrinos would lead to more (or less) primordial Helium than we see
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Neutrino mysteries
Not enough neutrinos are detected from the nuclear reactions in the Sun (“Solar neutrino problem”)
Oscillations between different types of neutrinos would solve the Solar neutrino problem
Oscillations also imply that neutrinos have a small amount of mass
electron neutrino
muon neutrino
March 25, 2003 Lynn Cominsky - Cosmology A350
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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
March 25, 2003 Lynn Cominsky - Cosmology A350
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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
March 25, 2003 Lynn Cominsky - Cosmology A350
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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
March 25, 2003 Lynn Cominsky - Cosmology A350
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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
March 25, 2003 Lynn Cominsky - Cosmology A350
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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 http://www.lngs.infn.it/
March 25, 2003 Lynn Cominsky - Cosmology A350
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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
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CDM models vs. density CDM models as a function of z (look-back time)
NowZ=0.5Z=1.0
Critical density
Low density
Largest structures are now just forming
March 25, 2003 Lynn Cominsky - Cosmology A350
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Dark Matter and Dark Energy
Assume that total = 1, then for
Ho = 65 km s-1 Mpc-1, we measure: b = 0.04 (+/- 0.001) (baryons)m = 0.4 (+/- 0.2) (all matter)0.001 << 0.1 (hot dark matter)= 0.6 – 0.7 (dark energy)
This makes the age of the Universe around 15 billion years
http://www.physics.ucla.edu/dm20/talks/1a.pdf
(Joel Primack’s talk at DM2000)
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Dark Matter Activity #2 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
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Web Resources
Astronomy picture of the Day http://antwrp.gsfc.nasa.gov/apod/astropix.html
Imagine the Universe http://imagine.gsfc.nasa.gov
Dark Matter 2000 (conference at UCLA) http://www.physics.ucla.edu/dm20/
Center for Particle Astrophysics http://cfpa.berkeley.edu/
Dark Matter telescope http://www.dmtelescope.org/darkmatter.html
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Web Resources
Jonathan Dursi’s Dark Matter Tutorials & Java applets
http://www.astro.queensu.ca/~dursi/dm-tutorial/dm0.html
MACHO project http://wwwmacho.mcmaster.ca/ National Center for Supercomputing
Applications http://www.ncsa.uiuc.edu/Cyberia/Cosmos/MystDarkMatter.html
Pete Newbury’s Gravitational Lens movies http://www.iam.ubc.ca/~newbury/lenses/research.html
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Web Resources
Alex Gary Markowitz’ Dark Matter Tutorial http://www.astro.ucla.edu/~agm/darkmtr.html
Martin White’s Dark Matter Models http://cfa-www.harvard.edu/~mwhite/modelcmp.html
Livermore Laboratory axion search http://www-phys.llnl.gov/N_Div/Axion/axion.html
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