Wilkinson Microwave Anisotropy Probe

Last updated

Wilkinson Microwave Anisotropy Probe
WMAP spacecraft.jpg
Artist's impression of WMAP
Explorer 80
Mission type CMBR Astronomy
Operator NASA
COSPAR ID 2001-027A
SATCAT no. 26859
Website map.gsfc.nasa.gov
Mission duration9 years, 1 month, 2 days (from launch to end collection of science data) [1]
Spacecraft properties
Manufacturer NASA  / NRAO
Launch mass835 kg (1,841 lb) [2]
Dry mass763 kg (1,682 lb)
Dimensions3.6 m × 5.1 m (12 ft × 17 ft)
Power419 W
Start of mission
Launch date19:46:46,June 30, 2001(UTC) (2001-06-30T19:46:46Z) [3]
Rocket Delta II 7425-10
Launch site Cape Canaveral SLC-17
End of mission
DeactivatedReceived last command October 20, 2010 (2010-10-20); transmitted last data 19 August 2010 [4]
Orbital parameters
Reference system L2 point
Regime Lissajous
Main telescope
Type Gregorian
Diameter1.4 m × 1.6 m (4.6 ft × 5.2 ft)
Wavelengths23 GHz to 94 GHz
WMAP collage.jpg
NASA collage of WMAP-related imagery (spacecraft, CMB spectrum and background image)

The Wilkinson Microwave Anisotropy Probe (WMAP), originally known as the Microwave Anisotropy Probe (MAP), was a spacecraft operating from 2001 to 2010 which measured temperature differences across the sky in the cosmic microwave background  (CMB) – the radiant heat remaining from the Big Bang. [5] [6] Headed by Professor Charles L. Bennett of Johns Hopkins University, the mission was developed in a joint partnership between the NASA Goddard Space Flight Center and Princeton University. [7] The WMAP spacecraft was launched on June 30, 2001 from Florida. The WMAP mission succeeded the COBE space mission and was the second medium-class (MIDEX) spacecraft in the NASA Explorers program. In 2003, MAP was renamed WMAP in honor of cosmologist David Todd Wilkinson (1935–2002), [7] who had been a member of the mission's science team. After nine years of operations, WMAP was switched off in 2010, following the launch of the more advanced Planck spacecraft by ESA in 2009.

Spacecraft Manned vehicle or unmanned machine designed to fly in outer space

A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, planetary exploration, and transportation of humans and cargo. All spacecraft except single-stage-to-orbit vehicles cannot get into space on their own, and require a launch vehicle.

Cosmic microwave background Universe events since the Big Bang 13.8 billion years ago

The cosmic microwave background, in Big Bang cosmology, is electromagnetic radiation as a remnant from an early stage of the universe, also known as "relic radiation". The CMB is faint cosmic background radiation filling all space. It is an important source of data on the early universe because it is the oldest electromagnetic radiation in the universe, dating to the epoch of recombination. With a traditional optical telescope, the space between stars and galaxies is completely dark. However, a sufficiently sensitive radio telescope shows a faint background noise, or glow, almost isotropic, that is not associated with any star, galaxy, or other object. This glow is strongest in the microwave region of the radio spectrum. The accidental discovery of the CMB in 1964 by American radio astronomers Arno Penzias and Robert Wilson was the culmination of work initiated in the 1940s, and earned the discoverers the 1978 Nobel Prize in Physics.

Big Bang The prevailing cosmological model for the observable universe

The Big Bang theory is the prevailing cosmological model for the observable universe from the earliest known periods through its subsequent large-scale evolution. The model describes how the universe expanded from a very high-density and high-temperature state, and offers a comprehensive explanation for a broad range of phenomena, including the abundance of light elements, the cosmic microwave background (CMB), large-scale structure and Hubble's law. If the observed conditions are extrapolated backwards in time using the known laws of physics, the prediction is that just before a period of very high density there was a singularity which is typically associated with the Big Bang. Current knowledge is insufficient to determine if the singularity was primordial.


WMAP's measurements played a key role in establishing the current Standard Model of Cosmology: the Lambda-CDM model. The WMAP data are very well fit by a universe that is dominated by dark energy in the form of a cosmological constant. Other cosmological data are also consistent, and together tightly constrain the Model. In the Lambda-CDM model of the universe, the age of the universe is 13.772±0.059 billion years. The WMAP mission's determination of the age of the universe is to better than 1% precision. [8] The current expansion rate of the universe is (see Hubble constant) 69.32±0.80 km·s−1·Mpc−1. The content of the universe currently consists of 4.628%±0.093% ordinary baryonic matter; 24.02%+0.88%
cold dark matter (CDM) that neither emits nor absorbs light; and 71.35%+0.95%
of dark energy in the form of a cosmological constant that accelerates the expansion of the universe. [9] Less than 1% of the current content of the universe is in neutrinos, but WMAP's measurements have found, for the first time in 2008, that the data prefer the existence of a cosmic neutrino background [10] with an effective number of neutrino species of 3.26±0.35. The contents point to a Euclidean flat geometry, with curvature () of −0.0027+0.0039
. The WMAP measurements also support the cosmic inflation paradigm in several ways, including the flatness measurement.

Lambda-CDM model Model of big-bang cosmology

The ΛCDM or Lambda-CDM model is a parametrization of the Big Bang cosmological model in which the universe contains three major components: first, a cosmological constant denoted by Lambda and associated with dark energy; second, the postulated cold dark matter ; and third, ordinary matter. It is frequently referred to as the standard model of Big Bang cosmology because it is the simplest model that provides a reasonably good account of the following properties of the cosmos:

Dark energy unknown property in cosmology that causes the expansion of the universe to accelerate.

In physical cosmology and astronomy, dark energy is an unknown form of energy which is hypothesized to permeate all of space, tending to accelerate the expansion of the universe. Dark energy is the most accepted hypothesis to explain the observations since the 1990s indicating that the universe is expanding at an accelerating rate.

Cosmological constant constant representing stress-energy density of the vacuum in Einsteins equation

In cosmology, the cosmological constant is the energy density of space, or vacuum energy, that arises in Albert Einstein's field equations of general relativity. It is closely associated to the concepts of dark energy and quintessence.

The mission has won various awards: according to Science magazine, the WMAP was the Breakthrough of the Year for 2003. [11] This mission's results papers were first and second in the "Super Hot Papers in Science Since 2003" list. [12] Of the all-time most referenced papers in physics and astronomy in the INSPIRE-HEP database, only three have been published since 2000, and all three are WMAP publications. Bennett, Lyman A. Page, Jr., and David N. Spergel, the latter both of Princeton University, shared the 2010 Shaw Prize in astronomy for their work on WMAP. [13] Bennett and the WMAP science team were awarded the 2012 Gruber Prize in cosmology. The 2018 Breakthrough Prize in Fundamental Physics was awarded to Bennett, Gary Hinshaw, Norman Jarosik, Page, Spergel and the WMAP science team.

INSPIRE-HEP is an open access digital library for the field of high energy physics (HEP). It is the successor of the Stanford Physics Information Retrieval System (SPIRES) database, the main literature database for high energy physics since the 1970s.

Lyman Page American astronomer

Lyman Alexander Page, Jr. is the James S. McDonnell Distinguished University Professor of Physics at Princeton University. He is an expert in observational cosmology and one of the original co-investigators for the WMAP probe that made precise observations of the cosmic background radiation, an electromagnetic echo of the Universe's Big Bang phase.

Shaw Prize award

The Shaw Prize is an annual award first presented by the Shaw Prize Foundation in 2004. Established in 2002 in Hong Kong, it honours

"individuals who are currently active in their respective fields and who have recently achieved distinguished and significant advances, who have made outstanding contributions in academic and scientific research or applications, or who in other domains have achieved excellence. The award is dedicated to furthering societal progress, enhancing quality of life, and enriching humanity's spiritual civilization."

As of October 2010, the WMAP spacecraft is derelict in a heliocentric graveyard orbit after 9 years of operations. [14] All WMAP data are released to the public and have been subject to careful scrutiny. The final official data release was the nine-year release in 2012. [15] [16]

Heliocentric orbit orbit around the barycenter of the Sun

A heliocentric orbit is an orbit around the barycenter of the Solar System, which is usually located within or very near the surface of the Sun. All planets, comets, and asteroids in the Solar System, and the Sun itself are in such orbits, as are many artificial probes and pieces of debris. The moons of planets in the Solar System, by contrast, are not in heliocentric orbits, as they orbit their respective planet.

Graveyard orbit supersynchronous orbit where spacecraft are intentionally placed at the end of their operational life

A graveyard orbit, also called a junk orbit or disposal orbit, is an orbit that lies away from common operational orbits. One significant graveyard orbit is a supersynchronous orbit well above geosynchronous orbit. Satellites are typically moved into such orbits at the end of their operational life to reduce the probability of colliding with operational spacecraft and generating space debris.

Some aspects of the data are statistically unusual for the Standard Model of Cosmology. For example, the largest angular-scale measurement, the quadrupole moment, is somewhat smaller than the Model would predict, but this discrepancy is not highly significant. [17] A large cold spot and other features of the data are more statistically significant, and research continues into these.


The universe's timeline, from the Big Bang to the WMAP CMB Timeline75.jpg
The universe's timeline, from the Big Bang to the WMAP

The WMAP objective was to measure the temperature differences in the Cosmic Microwave Background (CMB) radiation. The anisotropies then were used to measure the universe's geometry, content, and evolution; and to test the Big Bang model, and the cosmic inflation theory. [18] For that, the mission created a full-sky map of the CMB, with a 13 arcminute resolution via multi-frequency observation. The map required the fewest systematic errors, no correlated pixel noise, and accurate calibration, to ensure angular-scale accuracy greater than its resolution. [18] The map contains 3,145,728 pixels, and uses the HEALPix scheme to pixelize the sphere. [19] The telescope also measured the CMB's E-mode polarization, [18] and foreground polarization. [10] Its service life was 27 months; 3 to reach the L2 position, 2 years of observation. [18]

Geometry Branch of mathematics that studies the shape, size and position of objects

Geometry is a branch of mathematics concerned with questions of shape, size, relative position of figures, and the properties of space. A mathematician who works in the field of geometry is called a geometer.

HEALPix general class of spherical projections

HEALPix, an acronym for Hierarchical Equal Area isoLatitude Pixelisation of a 2-sphere, refers to either an algorithm for pixelisation of the 2-sphere or to the associated class of map projections. The pixelisation algorithm was devised in 1997 by Krzysztof M. Górski at the Theoretical Astrophysics Center in Copenhagen, Denmark, and first published as a preprint in 1998.

A comparison of the sensitivity of WMAP with COBE and Penzias and Wilson's telescope. Simulated data. BigBangNoise.jpg
A comparison of the sensitivity of WMAP with COBE and Penzias and Wilson's telescope. Simulated data.


The MAP mission was proposed to NASA in 1995, selected for definition study in 1996, and approved for development in 1997. [20] [21]

The WMAP was preceded by two missions to observe the CMB; (i) the Soviet RELIKT-1 that reported the upper-limit measurements of CMB anisotropies, and (ii) the U.S. COBE satellite that first reported large-scale CMB fluctuations. The WMAP was 45 times more sensitive, with 33 times the angular resolution of its COBE satellite predecessor. [22] The successor European Planck mission (operational 2009–2013) had a higher resolution and higher sensitivity than WMAP and observed in 9 frequency bands rather than WMAP's 5, allowing improved astrophysical foreground models.


WMAP spacecraft diagram WMAP spacecraft diagram.jpg
WMAP spacecraft diagram

The telescope's primary reflecting mirrors are a pair of Gregorian 1.4m × 1.6m dishes (facing opposite directions), that focus the signal onto a pair of 0.9m × 1.0m secondary reflecting mirrors. They are shaped for optimal performance: a carbon fibre shell upon a Korex core, thinly-coated with aluminium and silicon oxide. The secondary reflectors transmit the signals to the corrugated feedhorns that sit on a focal plane array box beneath the primary reflectors. [18]

Illustration of WMAP's receivers WMAP receivers.png
Illustration of WMAP's receivers

The receivers are polarization-sensitive differential radiometers measuring the difference between two telescope beams. The signal is amplified with HEMT low-noise amplifiers, built by the National Radio Astronomy Observatory. There are 20 feeds, 10 in each direction, from which a radiometer collects a signal; the measure is the difference in the sky signal from opposite directions. The directional separation azimuth is 180 degrees; the total angle is 141 degrees. [18] To improve subtraction of foreground signals from our Milky Way galaxy, the WMAP used five discrete radio frequency bands, from 23 GHz to 94 GHz. [18]

Properties of WMAP at different frequencies [18]
Central wavelength (mm)
Central frequency (GHz)2333416194
Bandwidth (GHz)
Beam size (arcminutes)52.839.630.62113.2
Number of radiometers22448
System temperature (K)29395992145
Sensitivity (mK s)

The WMAP's base is a 5.0m-diameter solar panel array that keeps the instruments in shadow during CMB observations, (by keeping the craft constantly angled at 22 degrees, relative to the Sun). Upon the array sit a bottom deck (supporting the warm components) and a top deck. The telescope's cold components: the focal-plane array and the mirrors, are separated from the warm components with a cylindrical, 33 cm-long thermal isolation shell atop the deck. [18]

Passive thermal radiators cool the WMAP to ca. 90 degrees K; they are connected to the low-noise amplifiers. The telescope consumes 419 W of power. The available telescope heaters are emergency-survival heaters, and there is a transmitter heater, used to warm them when off. The WMAP spacecraft's temperature is monitored with platinum resistance thermometers. [18]

The WMAP's calibration is effected with the CMB dipole and measurements of Jupiter; the beam patterns are measured against Jupiter. The telescope's data are relayed daily via a 2 GHz transponder providing a 667kbit/s downlink to a 70m Deep Space Network telescope. The spacecraft has two transponders, one a redundant back-up; they are minimally active – ca. 40 minutes daily – to minimize radio frequency interference. The telescope's position is maintained, in its three axes, with three reaction wheels, gyroscopes, two star trackers and sun sensors, and is steered with eight hydrazine thrusters. [18]

Launch, trajectory, and orbit

Animation of WMAP's trajectory
Animation of Wilkinson Microwave Anisotropy Probe trajectory.gif
Oblique view
Animation of Wilkinson Microwave Anisotropy Probe trajectory - Viewd from Earth.gif
Viewed from Earth
   Earth ·  WMAP

The WMAP spacecraft arrived at the Kennedy Space Center on April 20, 2001. After being tested for two months, it was launched via Delta II 7425 rocket on June 30, 2001. [20] [22] It began operating on its internal power five minutes before its launching, and continued so operating until the solar panel array deployed. The WMAP was activated and monitored while it cooled. On July 2, it began working, first with in-flight testing (from launching until August 17), then began constant, formal work. [22] Afterwards, it effected three Earth-Moon phase loops, measuring its sidelobes, then flew by the Moon on July 30, en route to the Sun-Earth L2 Lagrangian point, arriving there on October 1, 2001, becoming the first CMB observation mission posted there. [20]

Locating the spacecraft at Lagrange 2, (1.5 million kilometers from Earth) thermally stabilizes it and minimizes the contaminating solar, terrestrial, and lunar emissions registered. To view the entire sky, without looking to the Sun, the WMAP traces a path around L2 in a Lissajous orbit ca. 1.0 degree to 10 degrees, [18] with a 6-month period. [20] The telescope rotates once every 2 minutes, 9 seconds" (0.464 rpm) and precesses at the rate of 1 revolution per hour. [18] WMAP measured the entire sky every six months, and completed its first, full-sky observation in April 2002. [21]

Foreground radiation subtraction

The WMAP observed in five frequencies, permitting the measurement and subtraction of foreground contamination (from the Milky Way and extra-galactic sources) of the CMB. The main emission mechanisms are synchrotron radiation and free-free emission (dominating the lower frequencies), and astrophysical dust emissions (dominating the higher frequencies). The spectral properties of these emissions contribute different amounts to the five frequencies, thus permitting their identification and subtraction. [18]

Foreground contamination is removed in several ways. First, subtract extant emission maps from the WMAP's measurements; second, use the components' known spectral values to identify them; third, simultaneously fit the position and spectra data of the foreground emission, using extra data sets. Foreground contamination was reduced by using only the full-sky map portions with the least foreground contamination, while masking the remaining map portions. [18]

The five-year models of foreground emission, at different frequencies. Red = Synchrotron; Green = free-free; Blue = thermal dust.
WMAP 2008 23GHz foregrounds.png WMAP 2008 33GHz foregrounds.png WMAP 2008 41GHz foregrounds.png WMAP 2008 61GHz foregrounds.png WMAP 2008 94GHz foregrounds.png
23 GHz33 GHz41 GHz61 GHz94 GHz

Measurements and discoveries

One-year data release

1 year WMAP image of background cosmic radiation (2003). Baby Universe.jpg
1 year WMAP image of background cosmic radiation (2003).

On February 11, 2003, NASA published the first-year's worth of WMAP data. The latest calculated age and composition of the early universe were presented. In addition, an image of the early universe, that "contains such stunning detail, that it may be one of the most important scientific results of recent years" was presented. The newly released data surpass previous CMB measurements. [7]

Based upon the Lambda-CDM model, the WMAP team produced cosmological parameters from the WMAP's first-year results. Three sets are given below; the first and second sets are WMAP data; the difference is the addition of spectral indices, predictions of some inflationary models. The third data set combines the WMAP constraints with those from other CMB experiments (ACBAR and CBI), and constraints from the 2dF Galaxy Redshift Survey and Lyman alpha forest measurements. There are degenerations among the parameters, the most significant is between and ; the errors given are at 68% confidence. [23]

Best-fit cosmological parameters from WMAP one-year results [23]
ParameterSymbolBest fit (WMAP only)Best fit (WMAP, extra parameter)Best fit (all data)
Age of the universe (Ga)13.4±0.313.7±0.2
Hubble's constant ( km Mpc·s )72±570±571+4
Baryonic content0.024±0.0010.023±0.0020.0224±0.0009
Matter content0.14±0.020.14±0.020.135+0.008
Optical depth to reionization 0.166+0.076
Scalar spectral index0.99±0.040.93±0.070.93±0.03
Running of spectral index−0.047±0.04−0.031+0.016
Fluctuation amplitude at 8h−1 Mpc0.9±0.10.84±0.04
Total density of the universe1.02±0.02

Using the best-fit data and theoretical models, the WMAP team determined the times of important universal events, including the redshift of reionization, 17±4; the redshift of decoupling, 1089±1 (and the universe's age at decoupling, 379+8
); and the redshift of matter/radiation equality, 3233+194
. They determined the thickness of the surface of last scattering to be 195±2 in redshift, or 118+3
. They determined the current density of baryons, (2.5±0.1)×10−7 cm−1, and the ratio of baryons to photons, 6.1+0.3
. The WMAP's detection of an early reionization excluded warm dark matter. [23]

The team also examined Milky Way emissions at the WMAP frequencies, producing a 208-point source catalogue.

Three-year data release

3-year WMAP image of background cosmic radiation (2006). Microwave Sky polarization.png
3-year WMAP image of background cosmic radiation (2006).

The three-year WMAP data were released on March 17, 2006. The data included temperature and polarization measurements of the CMB, which provided further confirmation of the standard flat Lambda-CDM model and new evidence in support of inflation.

The 3-year WMAP data alone shows that the universe must have dark matter. Results were computed both only using WMAP data, and also with a mix of parameter constraints from other instruments, including other CMB experiments (ACBAR, CBI and BOOMERANG), SDSS, the 2dF Galaxy Redshift Survey, the Supernova Legacy Survey and constraints on the Hubble constant from the Hubble Space Telescope. [24]

Best-fit cosmological parameters from WMAP three-year results [24]
ParameterSymbolBest fit (WMAP only)
Age of the universe (Ga)13.73+0.16
Hubble's constant ( kmMpc·s )73.2+3.1
Baryonic content0.0229±0.00073
Matter content0.1277+0.0080
Optical depth to reionization [a] 0.089±0.030
Scalar spectral index0.958±0.016
Fluctuation amplitude at 8h−1 Mpc0.761+0.049
Tensor-to-scalar ratio [b] r< 0.65

[a] ^ Optical depth to reionization improved due to polarization measurements. [25]
[b] ^ < 0.30 when combined with SDSS data. No indication of non-gaussianity. [24]

Five-year data release

5-year WMAP image of background cosmic radiation (2008). WMAP 2008.png
5-year WMAP image of background cosmic radiation (2008).

The five-year WMAP data were released on February 28, 2008. The data included new evidence for the cosmic neutrino background, evidence that it took over half billion years for the first stars to reionize the universe, and new constraints on cosmic inflation. [26]

WMAP 2008 TT and TE spectra.png
The five-year total-intensity and polarization spectra from WMAP
WMAP 2008 universe content.png
Matter/energy content in the current universe (top) and at the time of photon decoupling in the recombination epoch 380,000 years after the Big Bang (bottom)

The improvement in the results came from both having an extra 2 years of measurements (the data set runs between midnight on August 10, 2001 to midnight of August 9, 2006), as well as using improved data processing techniques and a better characterization of the instrument, most notably of the beam shapes. They also make use of the 33 GHz observations for estimating cosmological parameters; previously only the 41 GHz and 61 GHz channels had been used.

Improved masks were used to remove foregrounds. [10] Improvements to the spectra were in the 3rd acoustic peak, and the polarization spectra. [10]

The measurements put constraints on the content of the universe at the time that the CMB was emitted; at the time 10% of the universe was made up of neutrinos, 12% of atoms, 15% of photons and 63% dark matter. The contribution of dark energy at the time was negligible. [26] It also constrained the content of the present-day universe; 4.6% atoms, 23% dark matter and 72% dark energy. [10]

The WMAP five-year data was combined with measurements from Type Ia supernova (SNe) and Baryon acoustic oscillations (BAO). [10]

The elliptical shape of the WMAP skymap is the result of a Mollweide projection. [27]

Best-fit cosmological parameters from WMAP five-year results [10]
ParameterSymbolBest fit (WMAP only)Best fit (WMAP + SNe + BAO)
Age of the universe (Ga)13.69±0.1313.72±0.12
Hubble's constant ( kmMpc·s )71.9+2.6
Baryonic content0.02273±0.000620.02267+0.00058
Cold dark matter content0.1099±0.00620.1131±0.0034
Dark energy content0.742±0.0300.726±0.015
Optical depth to reionization 0.087±0.0170.084±0.016
Scalar spectral index0.963+0.014
Running of spectral index−0.037±0.028−0.028±0.020
Fluctuation amplitude at 8h−1 Mpc0.796±0.0360.812±0.026
Total density of the universe1.099+0.100
Tensor-to-scalar ratior< 0.43< 0.22

The data puts limits on the value of the tensor-to-scalar ratio, r < 0.22 (95% certainty), which determines the level at which gravitational waves affect the polarization of the CMB, and also puts limits on the amount of primordial non-gaussianity. Improved constraints were put on the redshift of reionization, which is 10.9±1.4, the redshift of decoupling, 1090.88±0.72 (as well as age of universe at decoupling, 376.971+3.162
) and the redshift of matter/radiation equality, 3253+89
. [10]

The extragalactic source catalogue was expanded to include 390 sources, and variability was detected in the emission from Mars and Saturn. [10]

The five-year maps at different frequencies from WMAP with foregrounds (the red band)
WMAP 2008 23GHz.png WMAP 2008 33GHz.png WMAP 2008 41GHz.png WMAP 2008 61GHz.png WMAP 2008 94GHz.png
23 GHz33 GHz41 GHz61 GHz94 GHz

Seven-year data release

7-year WMAP image of background cosmic radiation (2010). WMAP 2010.png
7-year WMAP image of background cosmic radiation (2010).

The seven-year WMAP data were released on January 26, 2010. As part of this release, claims for inconsistencies with the standard model were investigated. [28] Most were shown not to be statistically significant, and likely due to a posteriori selection (where one sees a weird deviation, but fails to consider properly how hard one has been looking; a deviation with 1:1000 likelihood will typically be found if one tries one thousand times). For the deviations that do remain, there are no alternative cosmological ideas (for instance, there seem to be correlations with the ecliptic pole). It seems most likely these are due to other effects, with the report mentioning uncertainties in the precise beam shape and other possible small remaining instrumental and analysis issues.

The other confirmation of major significance is of the total amount of matter/energy in the universe in the form of dark energy – 72.8% (within 1.6%) as non 'particle' background, and dark matter – 22.7% (within 1.4%) of non baryonic (sub atomic) 'particle' energy. This leaves matter, or baryonic particles (atoms) at only 4.56% (within 0.16%).

Best-fit cosmological parameters from WMAP seven-year results [29]
ParameterSymbolBest fit (WMAP only)Best fit (WMAP + BAO [30] + H0 [31] )
Age of the universe (Ga)13.75±0.1313.75±0.11
Hubble's constant ( kmMpc·s )71.0±2.570.4+1.3
Baryon density0.0449±0.00280.0456±0.0016
Physical baryon density0.02258+0.00057
Dark matter density0.222±0.0260.227±0.014
Physical dark matter density0.1109±0.00560.1123±0.0035
Dark energy density0.734±0.0290.728+0.015
Fluctuation amplitude at 8h−1 Mpc0.801±0.0300.809±0.024
Scalar spectral index0.963±0.0140.963±0.012
Reionization optical depth 0.088±0.0150.087±0.014
*Total density of the universe1.080+0.093
*Tensor-to-scalar ratio, k0 = 0.002 Mpc−1r< 0.36 (95% CL)< 0.24 (95% CL)
*Running of spectral index, k0 = 0.002 Mpc−1−0.034±0.026−0.022±0.020
Note: * = Parameters for extended models
(parameters place limits on deviations
from the Lambda-CDM model) [29]
The Seven-year maps at different frequencies from WMAP with foregrounds (the red band)
WMAP 2010 23GHz.png WMAP 2010 33GHz.png WMAP 2010 41GHz.png WMAP 2010 61GHz.png WMAP 2010 94GHz.png
23 GHz33 GHz41 GHz61 GHz94 GHz

Nine-year data release

9-year WMAP image of background cosmic radiation (2012). Ilc 9yr moll4096.png
9-year WMAP image of background cosmic radiation (2012).

On December 20, 2012, the nine-year WMAP data and related images were released. 13.772±0.059 billion-year-old temperature fluctuations and a temperature range of ± 200 microkelvins are shown in the image. In addition, the study found that 95% of the early universe is composed of dark matter and dark energy, the curvature of space is less than 0.4 percent of "flat" and the universe emerged from the cosmic Dark Ages "about 400 million years" after the Big Bang. [15] [16] [32]

Best-fit cosmological parameters from WMAP nine-year results [16]
ParameterSymbolBest fit (WMAP only)Best fit (WMAP + eCMB + BAO + H0)
Age of the universe (Ga)13.74±0.1113.772±0.059
Hubble's constant ( kmMpc·s )70.0±2.269.32±0.80
Baryon density0.0463±0.00240.04628±0.00093
Physical baryon density0.02264±0.000500.02223±0.00033
Cold dark matter density0.233±0.0230.2402+0.0088
Physical cold dark matter density0.1138±0.00450.1153±0.0019
Dark energy density0.721±0.0250.7135+0.0095
Density fluctuations at 8h−1 Mpc0.821±0.0230.820+0.013
Scalar spectral index0.972±0.0130.9608±0.0080
Reionization optical depth 0.089±0.0140.081±0.012
Curvature1 −0.037+0.044
Tensor-to-scalar ratio (k0 = 0.002 Mpc−1)r< 0.38 (95% CL)< 0.13 (95% CL)
Running scalar spectral index−0.019±0.025−0.023±0.011

Main result

Interviews with Charles Bennett and Lyman Page about WMAP.

The main result of the mission is contained in the various oval maps of the CMB temperature differences. These oval images present the temperature distribution derived by the WMAP team from the observations by the telescope during the mission. Measured is the temperature obtained from a Planck's law interpretation of the microwave background. The oval map covers the whole sky. The results are a snapshot of the universe around 375,000 years after the Big Bang, which happened about 13.8 billion years ago. The microwave background is very homogeneous in temperature (the relative variations from the mean, which presently is still 2.7 kelvins, are only of the order of 5×10−5). The temperature variations corresponding to the local directions are presented through different colors (the "red" directions are hotter, the "blue" directions cooler than the average).

Follow-on missions and future measurements

The original timeline for WMAP gave it two years of observations; these were completed by September 2003. Mission extensions were granted in 2002, 2004, 2006, and 2008 giving the spacecraft a total of 9 observing years, which ended August 2010 [20] and in October 2010 the spacecraft was moved to a heliocentric "graveyard" orbit [14] outside L2, in which it orbits the Sun 14 times every 15 years.[ citation needed ]

Comparison of CMB results from COBE, WMAP and Planck - March 21, 2013. PIA16874-CobeWmapPlanckComparison-20130321.jpg
Comparison of CMB results from COBE, WMAP and Planck – March 21, 2013.

The Planck spacecraft, also measured the CMB from 2009 to 2013 and aims to refine the measurements made by WMAP, both in total intensity and polarization. Various ground- and balloon-based instruments have also made CMB contributions, and others are being constructed to do so. Many are aimed at searching for the B-mode polarization expected from the simplest models of inflation, including EBEX, Spider, BICEP2, Keck, QUIET, CLASS, SPTpol and others.

On 21 March 2013, the European-led research team behind the Planck cosmology probe released the mission's all-sky map of the cosmic microwave background. [33] [34] The map suggests the universe is slightly older than previously thought. According to the map, subtle fluctuations in temperature were imprinted on the deep sky when the cosmos was about 370,000 years old. The imprint reflects ripples that arose as early, in the existence of the universe, as the first nonillionth (10−30) of a second. Apparently, these ripples gave rise to the present vast cosmic web of galaxy clusters and dark matter. Based on the 2013 data, the universe contains 4.9% ordinary matter, 26.8% dark matter and 68.3% dark energy. On 5 February 2015, new data was released by the Planck mission, according to which the age of the universe is 13.799 ± 0.021 billion years old and the Hubble constant was measured to be 67.74 ± 0.46 (km/s)/Mpc. [35]

See also

Further reading

Related Research Articles

Cosmic Background Explorer space observatory

The Cosmic Background Explorer, also referred to as Explorer 66, was a satellite dedicated to cosmology, which operated from 1989 to 1993. Its goals were to investigate the cosmic microwave background radiation (CMB) of the universe and provide measurements that would help shape our understanding of the cosmos.

Reionization Universe events since the Big Bang 13.8 billion years ago

In the field of Big Bang theory, and cosmology, reionization is the process that caused the matter in the universe to reionize after the lapse of the "dark ages".

Observational cosmology

Observational cosmology is the study of the structure, the evolution and the origin of the universe through observation, using instruments such as telescopes and cosmic ray detectors.

Age of the universe Universe events since the Big Bang 13.8 billion years ago

In physical cosmology, the age of the universe is the time elapsed since the Big Bang. The current measurement of the age of the universe is 13.787±0.020 billion (109) years within the Lambda-CDM concordance model.The uncertainty has been narrowed down to 20 million years, based on a number of studies which all gave extremely similar figures for the age. These include studies of the microwave background radiation, and measurements by the Planck spacecraft, the Wilkinson Microwave Anisotropy Probe and other probes. Measurements of the cosmic background radiation give the cooling time of the universe since the Big Bang, and measurements of the expansion rate of the universe can be used to calculate its approximate age by extrapolating backwards in time.

In astronomical spectroscopy, the Gunn–Peterson trough is a feature of the spectra of quasars due to the presence of neutral hydrogen in the Intergalactic Medium (IGM). The trough is characterized by suppression of electromagnetic emission from the quasar at wavelengths less than that of the Lyman-alpha line at the redshift of the emitted light. This effect was originally predicted in 1965 by James E. Gunn and Bruce Peterson.

BOOMERanG experiment

In astronomy and observational cosmology, The BOOMERanG experiment was an experiment which measured the cosmic microwave background radiation of a part of the sky during three sub-orbital (high-altitude) balloon flights. It was the first experiment to make large, high-fidelity images of the CMB temperature anisotropies, and is best known for the discovery in 2000 that the geometry of the universe is close to flat, with similar results from the competing MAXIMA experiment.

<i>Planck</i> (spacecraft) Third medium mission of Horizon 2000; cosmic microwave background observatory for cosmology

Planck was a space observatory operated by the European Space Agency (ESA) from 2009 to 2013, which mapped the anisotropies of the cosmic microwave background (CMB) at microwave and infra-red frequencies, with high sensitivity and small angular resolution. The mission substantially improved upon observations made by the NASA Wilkinson Microwave Anisotropy Probe (WMAP). Planck provided a major source of information relevant to several cosmological and astrophysical issues, such as testing theories of the early Universe and the origin of cosmic structure. Since the end of its mission, Planck has defined the most precise measurements of several key cosmological parameters, including the average density of ordinary matter and dark matter in the Universe and the age of the universe.

Cosmic neutrino background

The cosmic neutrino background is the universe's background particle radiation composed of neutrinos. They are sometimes known as relic neutrinos.

Atacama Cosmology Telescope telescope in Chile

The Atacama Cosmology Telescope (ACT) is a six-metre telescope on Cerro Toco in the Atacama Desert in the north of Chile, near the Llano de Chajnantor Observatory. It is designed to make high-resolution, microwave-wavelength surveys of the sky in order to study the cosmic microwave background radiation (CMB). At an altitude of 5,190 metres (17,030 ft), it is one of the highest permanent, ground-based telescopes in the world.

Charles L. Bennett American astronomer

Charles L. Bennett is an American observational astrophysicist. He is a Bloomberg Distinguished Professor, the Alumni Centennial Professor of Physics and Astronomy and a Gilman Scholar at Johns Hopkins University. He is the Principal Investigator of NASA's highly successful Wilkinson Microwave Anisotropy Probe (WMAP).

Degree Angular Scale Interferometer

The Degree Angular Scale Interferometer (DASI) was a telescope installed at the U.S. National Science Foundation's Amundsen–Scott South Pole Station in Antarctica. It was a 13-element interferometer operating between 26 and 36 GHz in ten bands. The instrument is similar in design to the Cosmic Background Imager (CBI) and the Very Small Array (VSA). In 2001 The DASI team announced the most detailed measurements of the temperature, or power spectrum of the Cosmic microwave background (CMB). These results contained the first detection of the 2nd and 3rd acoustic peaks in the CMB, which were important evidence for inflation theory. This announcement was done in conjunction with the BOOMERanG and MAXIMA experiment. In 2002 the team reported the first detection of polarization anisotropies in the CMB.

CMB cold spot

The CMB Cold Spot or WMAP Cold Spot is a region of the sky seen in microwaves that has been found to be unusually large and cold relative to the expected properties of the cosmic microwave background radiation (CMBR). The "Cold Spot" is approximately 70 µK colder than the average CMB temperature, whereas the root mean square of typical temperature variations is only 18 µK. At some points, the "cold spot" deviates 140 µK colder than the average CMB temperature.

Dark flow A possible non-random component of the peculiar velocity of galaxy clusters

In astrophysics, dark flow is a theoretical non-random component of the peculiar velocity of galaxy clusters. The actual measured velocity is the sum of the velocity predicted by Hubble's Law plus a possible small and unexplained velocity flowing in a common direction.

Baryon acoustic oscillations fluctuations in the density of the visible baryonic matter of the universe, caused by acoustic density waves in the primordial plasma of the early universe

In cosmology, baryon acoustic oscillations (BAO) are fluctuations in the density of the visible baryonic matter of the universe, caused by acoustic density waves in the primordial plasma of the early universe. In the same way that supernovae provide a "standard candle" for astronomical observations, BAO matter clustering provides a "standard ruler" for length scale in cosmology. The length of this standard ruler is given by the maximum distance the acoustic waves could travel in the primordial plasma before the plasma cooled to the point where it became neutral atoms, which stopped the expansion of the plasma density waves, "freezing" them into place. The length of this standard ruler can be measured by looking at the large scale structure of matter using astronomical surveys. BAO measurements help cosmologists understand more about the nature of dark energy by constraining cosmological parameters.

The "Axis of Evil" is a name given to an anomaly in astronomical observations of the Cosmic Microwave Background (CMB). The anomaly appears to give the plane of the Solar System and hence the location of Earth a greater significance than might be expected by chance – a result which runs counter to expectations from the Copernican principle.

Michele Limon is an Italian research associate and assistant professor of Physics and Astronomy at Columbia University in the City of New York. Dr. Limon studied physics at the Università degli Studi di Milano in Milan, Italy and completed his post-doctoral work at the University of California, Berkeley. He has been conducting research for more than 20 years and has experience in the design of ground, balloon and space-based instrumentation. His academic specialties include Astrophysics, Cosmology, Instrumentation Development, and Cryogenics.

Jo Dunkley Professor of Physics and Astrophysical Sciences at Princeton University

Joanna Dunkley is a British astrophysicist and Professor of Physics at Princeton University. She works on the origin of the Universe and the Cosmic microwave background (CMB) using the Atacama Cosmology Telescope, the Simons Observatory and the Large Synoptic Survey Telescope (LSST).


  1. "WMAP News: Events Timeline".
  2. Citrin, L. "WMAP: The Wilkinson Microwave Anisotropy Probe" (PDF). Retrieved October 28, 2016.
  3. "WMAP News: Events Timeline". NASA. December 27, 2010. Retrieved July 8, 2015.
  4. https://map.gsfc.nasa.gov/news/events.html
  5. "Wilkinson Microwave Anisotropy Probe: Overview". Goddard Space Flight Center. August 4, 2009. Retrieved September 24, 2009. The WMAP (Wilkinson Microwave Anisotropy Probe) mission is designed to determine the geometry, content, and evolution of the universe via a 13 arcminute FWHM resolution full sky map of the temperature anisotropy of the cosmic microwave background radiation.
  6. "Tests of Big Bang: The CMB". Goddard Space Flight Center. July 2009. Retrieved September 24, 2009. Only with very sensitive instruments, such as COBE and WMAP, can cosmologists detect fluctuations in the cosmic microwave background temperature. By studying these fluctuations, cosmologists can learn about the origin of galaxies and large-scale structures of galaxies, and they can measure the basic parameters of the Big Bang theory.
  7. 1 2 3 "New image of infant universe reveals era of first stars, age of cosmos, and more". NASA / WMAP team. February 11, 2003. Archived from the original on February 27, 2008. Retrieved April 27, 2008.
  8. Glenday, C., ed. (2010). Guinness World Records 2010: Thousands of new records in The Book of the Decade! . Bantam. p. 7. ISBN   978-0553593372.
  9. Beringer, J.; et al. (Particle Data Group) (2013). "Astrophysics and Cosmology". Review of Particle Physics .
  10. 1 2 3 4 5 6 7 8 9 Hinshaw et al. (2009)
  11. Seife (2003)
  12. ""Super Hot" Papers in Science". in-cites. October 2005. Retrieved April 26, 2008.
  13. "Announcement of the Shaw Laureates 2010". Archived from the original on June 4, 2010.Cite uses deprecated parameter |deadurl= (help)
  14. 1 2 O'Neill, I. (October 7, 2010). "Mission Complete! WMAP Fires Its Thrusters For The Last Time". Discovery News . Retrieved January 27, 2013.
  15. 1 2 Gannon, M. (December 21, 2012). "New 'Baby Picture' of Universe Unveiled". Space.com . Retrieved December 21, 2012.
  16. 1 2 3 Bennett, C. L.; et al. (2013). "Nine-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Final Maps and Results". Astrophysical Journal Supplement . 208 (2): 20. arXiv: 1212.5225 . Bibcode:2013ApJS..208...20B. doi:10.1088/0067-0049/208/2/20.
  17. O'Dwyer, I. J.; et al. (2004). "Bayesian Power Spectrum Analysis of the First-Year Wilkinson Microwave Anisotropy Probe Data". Astrophysical Journal Letters . 617 (2): L99–L102. arXiv: astro-ph/0407027 . Bibcode:2004ApJ...617L..99O. doi:10.1086/427386.
  18. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Bennett et al. (2003a)
  19. Bennett et al. (2003b)
  20. 1 2 3 4 5 "WMAP News: Facts". NASA. April 22, 2008. Retrieved April 27, 2008.
  21. 1 2 "WMAP News: Events". NASA. April 17, 2008. Retrieved April 27, 2008.
  22. 1 2 3 Limon et al. (2008)
  23. 1 2 3 Spergel et al. (2003)
  24. 1 2 3 Spergel et al. (2007)
  25. Hinshaw et al. (2007)
  26. 1 2 "WMAP Press Release — WMAP reveals neutrinos, end of dark ages, first second of universe". NASA / WMAP team. March 7, 2008. Retrieved April 27, 2008.
  27. WMAP 1-year Paper Figures, Bennett, et al.
  28. Bennett, C. L.; et al. (2011). "Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Are There Cosmic Microwave Background Anomalies?". Astrophysical Journal Supplement Series . 192 (2): 17. arXiv: 1001.4758 . Bibcode:2011ApJS..192...17B. doi:10.1088/0067-0049/192/2/17.
  29. 1 2 Table 8 on p. 39 of Jarosik, N.; et al. "Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Sky Maps, Systematic Errors, and Basic Results" (PDF). WMAP Collaboration. nasa.gov. Retrieved December 4, 2010. (from NASA's WMAP Documents page)
  30. Percival, Will J.; et al. (February 2010). "Baryon Acoustic Oscillations in the Sloan Digital Sky Survey Data Release 7 Galaxy Sample". Monthly Notices of the Royal Astronomical Society . 401 (4): 2148–2168. arXiv: 0907.1660 . Bibcode:2010MNRAS.401.2148P. doi:10.1111/j.1365-2966.2009.15812.x.
  31. Riess, Adam G.; et al. "A Redetermination of the Hubble Constant with the Hubble Space Telescope from a Differential Distance Ladder" (PDF). hubblesite.org. Retrieved December 4, 2010.
  32. Hinshaw et al., 2013
  33. Clavin, Whitney; Harrington, J.D. (March 21, 2013). "Planck Mission Brings Universe Into Sharp Focus". NASA . Retrieved March 21, 2013.
  34. Staff (March 21, 2013). "Mapping the Early Universe". New York Times . Retrieved March 23, 2013.
  35. Ade, P. A.; et al. (2016). "Planck 2015 results. XIII. Cosmological parameters". Astronomy & Astrophysics . 594: A13. arXiv: 1502.01589 . Bibcode:2016A&A...594A..13P. doi:10.1051/0004-6361/201525830.

Primary sources