July 28, 2004

Part I: Dark Matter and Dark Energy

Part II: Beyond Einstein

July 28, 2004

July 28, 2004

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

KPNO image of the Coma cluster of galaxies - almost every object in this picture is a galaxy! Coma is 300 million light years away.

July 28, 2004

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!

July 28, 2004

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!

July 28, 2004

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

July 28, 2004

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)

July 28, 2004

Standard Candles

• If you have two light sources that you know are the same brightness

• The apparent brightness of the distant source will allow you to calculate its distance, compared to the nearby source

• This is because the brightness decreases like 1/(distance)2

movie

July 28, 2004

Type 1a Supernovae

• Type Ia supernovae are “standard candles”• Occur in a binary system in which a white dwarf

star accretes beyond the 1.4 Mo Chandrasekhar limit and collapses and explodes

• Decay time of light curve is correlated to absolute luminosity

• Luminosity comes from the radioactive decay of Cobalt and Nickel into Iron

• Some Type Ia supernovae are in galaxies with Cepheid variables

• Good to 20% as a distance measure

July 28, 2004

Recall Geometry

= density of the universe / critical density

hyperbolic geometry

flat or Euclidean

spherical geometry

July 28, 2004

The fate of the Universe

• As the universe expands, the matter spreads out, with its density decreasing in inverse proportion to the volume. (V = 4r3/3 for a sphere)

• The strength of the curvature effect decreases less rapidly, as the inverse of the surface area. (A = 4r2 for a sphere)

• So, in the standard picture of cosmology, geometry (curvature) ultimately gains control of the expansion of the universe.

July 28, 2004

Cosmological parameters

• In order to find the matter density of the Universe, you must measure its total amount of matter and radiant energy (since E=mc2), including:– All the matter we see– All the dark matter that we don’t see but we feel– All the energy from starlight, background radiation, etc.

• The part of the total density/critical density that could be due to matter and/or energy = M

• Current measurements : M< 0.3• In the pre-1998 picture, this meant an open

universe

July 28, 2004 0 0.2 10.80.60.4

Supernovae & Cosmology

M = matter

= dark energy

Redshift

July 28, 2004

(total)M +

This plot shows the allowed values of the densities of matter (including dark matter and light) vs. dark energy

Critical density

Perlmutter et al.

WMAP results

Matter results

July 28, 2004

Accelerating Universe

• A combination of supernova data from Perlmutter et al. (and a second group Schmidt et al.) strongly suggest that if =

0.3 and WMAP results indicate that total = 1

There is some type of dark energy which is

causing the expansion of the Universe to accelerate

July 28, 2004

Views of the Universe

July 28, 2004

Geometry is not Destiny

• One type of dark energy could be the cosmological constant () – added to Einstein’s GR equations to counter the predicted expansion of the Universe – Einstein called his “biggest blunder”

• Another popular theory is Quintessence• If dark energy plays a significant role in the

evolution of the universe, then in all likelihood the universe will continue to expand forever.

July 28, 2004

Composition of the Cosmos

July 28, 2004

Educational Learning Experience

• Each group will investigate what is known about a proposed type of either Dark Matter or Dark Energy

• What is the evidence for this type?

• What experiments have been done and/or are planned to detect it?

• How would you teach this to your class?

July 28, 2004

Presentations and Debrief

• Presentations by EAs

• Debrief slides follow

July 28, 2004

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

July 28, 2004

Baryonic - Brown Dwarfs

• Mass around 0.08 Mo

• Do not undergo nuclear burning in cores

• First brown dwarf star Gliese 229B

July 28, 2004

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!

July 28, 2004

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)

July 28, 2004

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

July 28, 2004

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

July 28, 2004

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…..

July 28, 2004

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

July 28, 2004

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

July 28, 2004

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

July 28, 2004

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

July 28, 2004

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

July 28, 2004

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

July 28, 2004

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

July 28, 2004

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

July 28, 2004

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

July 28, 2004

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/

July 28, 2004

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

July 28, 2004

Vacuum Energy

• The cosmological constant is related to the “zero-point energy” of the Universe which comes from the quantum fluctuations of the vacuum.

• However, the vacuum energy density is 10120 too high to allow structure formation to occur

• Something must be canceling almost all of the vacuum energy in order for us to be here

• And that something must have arranged for the exact 70% of critical density to be left over at our current time, 13.7 billion years later

July 28, 2004

Quintessence

• Quintessence is another theory for dark energy that involves a dynamic, time-evolving and spatially dependent form of energy.

• It makes slightly different predictions for the acceleration

• It’s name refers to a “fifth essence” or force

July 28, 2004

Gravity and pressure

RelativisticG = +3PP = /3 G = 4> 0

Non-relativistic

G = +3P

P = 0

G = > 0

QuintessenceG = +3P P = -2/3 < 0

G = -

G = +3P P = -< 0

G = - 2

July 28, 2004

Going Beyond Einstein

• Show video here

July 28, 2004

Going Beyond Einstein

• NASA is beginning a new program to test predictions of Einstein’s theories:– What happens at the edge of a black hole?– What powered the Big Bang?– What is the mysterious Dark Energy that is

pulling the Universe apart?

• Do Einstein’s theories completely describe our Universe?

July 28, 2004

BE Great Observatories

Constellation X LISA

Four X-ray telescopes flying in formation

Three satellites, each with 2 lasers and 2 test masses

July 28, 2004

Constellation X

• Four X-ray satellites that point at the same place

• Launched two at a time• High resolution x-ray spectra• Large collecting area• Delayed until at least 2013

July 28, 2004

Measuring spin

Constellation X will be able to tell spinning (Kerr) black holes from non-spinning (Schwarzschild) black holes

Comparison of Line Profiles from Constellation-X

Energy (keV)

July 28, 2004

Gravitational Radiation

The strongest signal comes from two orbiting black holes

Black hole mergers in distant galaxies will test General Relativity in the extreme

• General Relativity predicts the existence of gravitational radiation waves of gravity that travel at the speed of light

July 28, 2004

Measuring Black Holes• Mass and spin of black hole can be measured

from the gravitational radiation patterns emitted in different situations

Distorted Schwarzschild black hole

Distorted Kerr black hole

July 28, 2004

Colliding Black Holes• Spiral waveform can be calculated reliably• Ringdown after merger tells you the mass• Larger computers needed to predict the actual

collision waveforms

July 28, 2004

Colliding Black Holes

• Movie shows the event horizons merging as two black holes collide to form one larger black hole

movie

July 28, 2004

Colliding Black Holes

• Movie shows the blue and yellow gravitational waves emitted as the green event horizons of two black holes collide to form one larger black hole

movie

July 28, 2004

Laser Interferometer Space Antenna (LISA)

• BH binaries• BH collisions• Galactic binaries

Launch 2013+

July 28, 2004

Beyond Einstein Probes

Census of hidden

Black Holes

Dark Energy InflationBlack Hole Finder

Measure expansion

history

Polarization of CMB

July 28, 2004

BE Mission Concept Studies

• Black Hole Finder:– EXIST: Energetic X-ray Imaging Survey

Telescope – SSU is leading E/PO

• Dark Energy Probe:– Leading concept is SNAP: Supernova

Acceleration Probe– NASA and DOE have signed agreement

for “Joint Dark Energy Mission”

July 28, 2004

Beyond Einstein Vision Missions

Big Bang Observer Black Hole Imager

Direct detection of gravitational waves from Big Bang

Resolved image of the Event Horizon

July 28, 2004

Dark Universe Observatory

• SSU is leading E/PO for DUO

• Studies x-rays from galaxy clusters to map out dark matter and trace dark energy evolution as a function of time

• http://epo.sonoma.edu/duo

• Currently in Phase A Concept Study Review – site visits in September

July 28, 2004

NuSTAR

• SSU is also leading E/PO for NuSTAR – Nuclear Spectroscopic Telescope Array

• Studies hard x-rays from black holes, nuclear lines and supernovae

• http://epo.sonoma.edu/nustar• Results of the competition will be known

in November (there are also 3 other Sun-Earth Connection missions)

July 28, 2004

Some last words from Einstein

• “The most incomprehensible thing about the Universe is that it is comprehensible”

July 28, 2004

Reflection and Debrief

July 28, 2004

Reflection and Debrief(Evaluate)

• Now what do we know?

• What are the big ideas here?

• What do our students need to know?

• Is there anything else we need to know?

• Misconceptions

(take notes)

July 28, 2004

Reflection and Debrief (Evaluate)

• What are some of the effective ways to teaching these topics?

• Standards???

(take notes)

July 28, 2004

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

July 28, 2004

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

July 28, 2004

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