March 25, 2003Lynn Cominsky - Cosmology A3501 Professor Lynn Cominsky Department of Physics and...

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: [email protected]

Astronomy 350Cosmology


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Group 8

Robert Angeli Jacy Maka Ryan McDaniel Rena Morabe


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Composition of the Cosmos


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Kepler’s Third Law movieP2 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 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


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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!


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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 = (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


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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!


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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!

Mt. Stromlo Observatory in Australia (in better days)


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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 galaxy’s 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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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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Spherical lens Perfect alignment Note formation of

Einstein’s rings

movie


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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


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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


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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


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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


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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 < 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

Cryostat holds T= 0.01 K

CDMS Lab 35 feet under Stanford


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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 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


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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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March 25, 2003Lynn Cominsky - Cosmology A3501 Professor Lynn Cominsky Department of Physics and...

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