WMAP

The Wilkinson Microwave Anisotropy Probe was designed to measure the CMB. –Launched in 2001 –Ended 2010 Microwave antenna includes five frequency bands. –22 to 90 GHz –High angular and frequency resolution

L2 Orbit WMAP uses the stable L2 point in the sun-earth system. –About 4 times lunar orbit –Always faces away from the sun –Complete sweep every 6 months WMAP orbits L2 in an elliptical orbit. –Onboard propulsion to correct orbit

Anisotropy Spatial anisotropy is very small. – K fluctuations Absolute temperature measurement includes statistical and systematic error. Coherent errors are the same for all points. –Remove error by measuring differences not absolutes

Precision Instrument WMAP combines precise frequency and spatial resolution. –20 uK statistical –5 uK systematics –0.3° spatial pixel Back-to-back telescopes provide differential measurements. –140° separation

Differential Signal Processing

Shape of Space Space can be flat or curved. –3D not just 2D The Riemann curvature parameter determines the direction and extent of curvature. –Positive curvature closed –Negative curvature open

Collapsing Universe Matter contributes to gravitation. –Pulls the universe together The orange line represents a universe dominated by high density matter. –Few billion years old –Eventual collapse

Critical Density At critical density the matter is sufficient for a flat universe. –Asymptotically reaches maximum size –Green curve At lower density gravity cannot stop expansion. –Expansion slows but continues –Blue curve

Dark Energy Dark energy represents energy tied in space itself. This energy drives expansion. –Effectively opposes gravity –Fraction sets the rate The red curve has a large fraction of the matter as dark energy.

Initial Appearance The initial appearance of matter is called the Big Bang. –Not really an explosion –High density matter and energy Since space is expanding there is no central point. Cooling radiation become the cosmic microwave background.

One Second The temperature decreases as the universe expands. –One second = K At this point protons and neutrons can fuse into light nuclei. –Proton + neutron = deuterium –Deuterium + deuterium = helium 4 –Also helium 3 and lithium

Nucleosynthesis The density of ordinary matter determines the likely mix of light nuclei. WMAP measures ordinary matter at 4.6% of the total. –Predicted mix matches other observations

Hot Radiation For 300,000 years it was too hot for atoms to form. The plasma and free electrons were opaque. When the temperature fell to 3000 K, atoms formed. The universe was transparent, with a burst of light everywhere.

Blackbody Radiation The CMB spectrum is consistent with radiation at K. The peak is in the microwave region. –Fluctuations are an order of magnitude smaller

Solar Motion Solar motion can be seen in low resolution anisotropy. –Blue K –Red K Central line is the galactic plane.

CMB Anisotropy After subtraction the residual anisotropy represents the CMB. –Blue K –Red K Central line is the galactic plane.

Matter Fractions The anisotropy points at the fraction of matter of different types. –Ordinary matter 4.6% –Cold dark matter 23% –Dark energy 72%

Shape and Age The mix of matter is consistent with a flat universe (2%). –Determine H to within 5% –73.5 (km/s)/Mpc The Hubble constant along with matter mixture sets the age. –Low matter density –1/H 0 = 13.7 billion years (1%)