wmap. the wilkinson microwave anisotropy probe was designed to measure the cmb. –launched in 2001...
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![Page 1: WMAP. The Wilkinson Microwave Anisotropy Probe was designed to measure the CMB. –Launched in 2001 –Ended 2010 Microwave antenna includes five frequency](https://reader030.vdocument.in/reader030/viewer/2022032703/56649d375503460f94a0fbf7/html5/thumbnails/1.jpg)
WMAP
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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
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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
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Anisotropy
• Spatial anisotropy is very small.
– 0.0002 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
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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
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Differential Signal Processing
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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
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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
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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
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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.
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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.
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One Second
• The temperature decreases as the universe expands.
– One second = 1010 K
• At this point protons and neutrons can fuse into light nuclei.
– Proton + neutron = deuterium
– Deuterium + deuterium = helium 4
– Also helium 3 and lithium
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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
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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.
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Blackbody Radiation
• The CMB spectrum is consistent with radiation at 2.725 K.
• The peak is in the microwave region.
– Fluctuations are an order of magnitude smaller
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Solar Motion
• Solar motion can be seen in low resolution anisotropy.
– Blue 2.721 K
– Red 2.729 K
• Central line is the galactic plane.
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CMB Anisotropy
• After subtraction the residual anisotropy represents the CMB.
– Blue 2.7249 K
– Red 2.7251 K
• Central line is the galactic plane.
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Matter Fractions
• The anisotropy points at the fraction of matter of different types.
– Ordinary matter 4.6%
– Cold dark matter 23%
– Dark energy 72%
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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/H0 = 13.7 billion years (1%)