Professor Lynn Cominsky

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Astronomy 350Cosmology

• Professor Lynn Cominsky
• Department of Physics and Astronomy
• Offices Darwin 329A and NASA EPO
• [phone]
• Best way to reach me lynnc_at_charmian.sonoma.edu

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Group 8

• Robert Angeli
• Jacy Maka
• Ryan McDaniel
• Rena Morabe

Let's hear it for Group 8!
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Composition of the Cosmos
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Keplers Third Law movie

• P2 is proportional to a3

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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.
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Virial Theorem

• Stable galaxies should obey this law 2K -U
• where K½mV2 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 MV2r/aG.
• Measure M, r and V2 from observations of the
  galaxies then use M and r to calculate Vvirial
• Compare Vmeasured to Vvirial
• Vmeasured gt Vvirial which implies M was too small

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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

v2GM/r where M is mass within a radius r Since
v flattens out, M must increase with increasing r!
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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

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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!

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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)

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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

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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
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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!

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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

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Baryonic - Brown Dwarfs

• Mass 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, lt 6
  of mass of galaxy halo

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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

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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!

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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

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Gravitational Microlensing

• Scale not large enough to form two separate images

movie
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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 galaxys central region

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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..

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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
• Einsteins rings can be formed for the correct
  alignment

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Strong Gravitational Lensing

• Spherical lens
• Perfect alignment
• Note formation of Einsteins rings

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Strong Gravitational Lensing

• Elliptical lens
• Einsteins rings break up into arcs if you can
  only see the brightest parts

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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

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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

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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

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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

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Baryonic dust

• Dust is made of elements heavier than Helium,
  which were previously produced by stars (lt2 of
  total)
• Dust absorbs and reradiates background light

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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 balance

electron
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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
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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

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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

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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 lt 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

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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

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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/

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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 dont move very fast and clump to
  form small structures first bottom up

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CDM models vs. density

• CDM models as a function of z (look-back time)

Largest structures are now just forming
Critical density
Low density
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Dark Matter and Dark Energy

• Assume that Wtotal 1, then for
• Ho 65 km s-1 Mpc-1, we measure
• Wb 0.04 (/- 0.001) (baryons)
• Wm 0.4 (/- 0.2) (all matter)
• 0.001 lt Wnlt 0.1 (hot dark matter)
• WL 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 Primacks 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.na
  sa.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/d
  arkmatter.html

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Web Resources

• Jonathan Dursis 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/MystDarkMa
  tter.html
• Pete Newburys Gravitational Lens movies
  http//www.iam.ubc.ca/newbury/lenses/research.htm
  l

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Web Resources

• Alex Gary Markowitz Dark Matter Tutorial
  http//www.astro.ucla.edu/agm/darkmtr.html
• Martin Whites 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