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The Wilkinson Microwave Anisotropy Probe (WMAP), originally known as the Microwave Anisotropy Probe (MAP and Explorer 80), was a
NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...
spacecraft operating from 2001 to 2010 which measured temperature differences across the sky in the
cosmic microwave background In Big Bang cosmology the cosmic microwave background (CMB, CMBR) is electromagnetic radiation that is a remnant from an early stage of the universe, also known as "relic radiation". The CMB is faint cosmic background radiation filling all spac ...
(CMB) – the radiant heat remaining from the
Big Bang The Big Bang event is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological models of the Big Bang explain the evolution of the observable universe from the ...
. Headed by Professor Charles L. Bennett of
Johns Hopkins University Johns Hopkins University (Johns Hopkins, Hopkins, or JHU) is a private research university in Baltimore, Maryland. Founded in 1876, Johns Hopkins is the oldest research university in the United States and in the western hemisphere. It consi ...
, the mission was developed in a joint partnership between the NASA
Goddard Space Flight Center The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory located approximately northeast of Washington, D.C. in Greenbelt, Maryland, United States. Established on May 1, 1959 as NASA's first space flight center, GSFC empl ...
and
Princeton University Princeton University is a private research university in Princeton, New Jersey. Founded in 1746 in Elizabeth as the College of New Jersey, Princeton is the fourth-oldest institution of higher education in the United States and one of the ...
. The WMAP spacecraft was launched on 30 June 2001 from
Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and ...
. The WMAP mission succeeded the COBE space mission and was the second medium-class (MIDEX) spacecraft in the NASA Explorer program. In 2003, MAP was renamed WMAP in honor of cosmologist David Todd Wilkinson (1935–2002), 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
European Space Agency , owners = , headquarters = Paris, Île-de-France, France , coordinates = , spaceport = Guiana Space Centre , seal = File:ESA emblem seal.png , seal_size = 130px , image = Views in the Main Control Room (120 ...
(ESA) in 2009. WMAP's measurements played a key role in establishing the current Standard Model of Cosmology: the
Lambda-CDM model The ΛCDM (Lambda cold dark matter) or Lambda-CDM model is a parameterization of the Big Bang cosmological model in which the universe contains three major components: first, a cosmological constant denoted by Lambda ( Greek Λ) associated ...
. The WMAP data are very well fit by a universe that is dominated by
dark energy In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales. The first observational evidence for its existence came from measurements of supernovas, which showed that the univ ...
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 billion years. The WMAP mission's determination of the age of the universe is to better than 1% precision. The current expansion rate of the universe is (see
Hubble constant Hubble's law, also known as the Hubble–Lemaître law, is the observation in physical cosmology that galaxies are moving away from Earth at speeds proportional to their distance. In other words, the farther they are, the faster they are moving ...
) . The content of the universe currently consists of ordinary
baryonic matter In particle physics, a baryon is a type of composite subatomic particle which contains an odd number of valence quarks (at least 3). Baryons belong to the hadron family of particles; hadrons are composed of quarks. Baryons are also classifie ...
;
cold dark matter In cosmology and physics, cold dark matter (CDM) is a hypothetical type of dark matter. According to the current standard model of cosmology, Lambda-CDM model, approximately 27% of the universe is dark matter and 68% is dark energy, with only a sm ...
(CDM) that neither emits nor absorbs light; and of
dark energy In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales. The first observational evidence for its existence came from measurements of supernovas, which showed that the univ ...
in the form of a cosmological constant that accelerates the
expansion of the universe The expansion of the universe is the increase in distance between any two given gravitationally unbound parts of the observable universe with time. It is an intrinsic expansion whereby the scale of space itself changes. The universe does not ex ...
. 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 The cosmic neutrino background (CNB or CB) is the universe's background particle radiation composed of neutrinos. They are sometimes known as relic neutrinos. The CB is a relic of the Big Bang; while the cosmic microwave background radiation ( ...
Hinshaw et al. (2009) with an effective number of neutrino species of . The contents point to a Euclidean flat geometry, with curvature (\Omega_) of . The WMAP measurements also support the
cosmic inflation In physical cosmology, cosmic inflation, cosmological inflation, or just inflation, is a theory of exponential expansion of space in the early universe. The inflationary epoch lasted from  seconds after the conjectured Big Bang singular ...
paradigm in several ways, including the flatness measurement. The mission has won various awards: according to ''Science'' magazine, the WMAP was the ''Breakthrough of the Year for 2003''.Seife (2003) This mission's results papers were first and second in the "Super Hot Papers in Science Since 2003" list. Of the all-time most referenced papers in physics and astronomy in the
INSPIRE-HEP 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 19 ...
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 The Shaw Prize is an annual award presented by the Shaw Prize Foundation. Established in 2002 in Hong Kong, it honours "individuals who are currently active in their respective fields and who have recently achieved distinguished and signifi ...
in astronomy for their work on WMAP. Bennett and the WMAP science team were awarded the 2012 Gruber Prize in cosmology. The 2018
Breakthrough Prize in Fundamental Physics The Breakthrough Prize in Fundamental Physics is one of the Breakthrough Prizes, awarded by the Breakthrough Prize Board. Initially named Fundamental Physics Prize, it was founded in July 2012 by Russia-born Israeli entrepreneur, venture c ...
was awarded to Bennett, Gary Hinshaw, Norman Jarosik, Page, Spergel, and the WMAP science team. In October 2010, the WMAP spacecraft was derelict in a
heliocentric Heliocentrism (also known as the Heliocentric model) is the astronomical model in which the Earth and planets revolve around the Sun at the center of the universe. Historically, heliocentrism was opposed to geocentrism, which placed the Earth ...
graveyard orbit after completing 9 years of operations. 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. Some aspects of the data are statistically unusual for the Standard Model of Cosmology. For example, the largest angular-scale measurement, the
quadrupole moment A quadrupole or quadrapole is one of a sequence of configurations of things like electric charge or current, or gravitational mass that can exist in ideal form, but it is usually just part of a multipole expansion of a more complex structure ref ...
, is somewhat smaller than the Model would predict, but this discrepancy is not highly significant. A large cold spot and other features of the data are more statistically significant, and research continues into these.


Objectives

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 Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
; and to test the
Big Bang The Big Bang event is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological models of the Big Bang explain the evolution of the observable universe from the ...
model, and the
cosmic inflation In physical cosmology, cosmic inflation, cosmological inflation, or just inflation, is a theory of exponential expansion of space in the early universe. The inflationary epoch lasted from  seconds after the conjectured Big Bang singular ...
theory. For that, the mission created a full-sky map of the CMB, with a 13
arcminutes A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The n ...
resolution via multi-frequency observation. The map required the fewest
systematic error Observational error (or measurement error) is the difference between a measured value of a quantity and its true value.Dodge, Y. (2003) ''The Oxford Dictionary of Statistical Terms'', OUP. In statistics, an error is not necessarily a " mistak ...
s, no correlated pixel noise, and accurate calibration, to ensure angular-scale accuracy greater than its resolution.Bennett et al. (2003a) The map contains 3,145,728 pixels, and uses the
HEALPix HEALPix (sometimes written as Healpix), an acronym for Hierarchical Equal Area isoLatitude Pixelisation of a 2-sphere, is an algorithm for pixelisation of the 2-sphere and the associated class of map projections. The pixelisation algorithm was de ...
scheme to pixelize the sphere.Bennett et al. (2003b) The telescope also measured the CMB's E-mode polarization, and foreground polarization. Its service life was 27 months; 3 to reach the position, and 2 years of observation.


Development

The MAP mission was proposed to NASA in 1995, selected for definition study in 1996, and approved for development in 1997. 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.Limon et al. (2008) 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.


Spacecraft

The telescope's primary reflecting mirrors are a pair of Gregorian dishes (facing opposite directions), that focus the signal onto a pair of secondary reflecting mirrors. They are shaped for optimal performance: a carbon fibre shell upon a Korex core, thinly-coated with aluminium and
silicon oxide Silicon oxide may refer to either of the following: * Silicon dioxide or quartz, SiO2, very well characterized *Silicon monoxide Silicon monoxide is the chemical compound with the formula SiO where silicon is present in the oxidation state +2. In ...
. The secondary reflectors transmit the signals to the corrugated feedhorns that sit on a
focal plane In Gaussian optics, the cardinal points consist of three pairs of points located on the optical axis of a rotationally symmetric, focal, optical system. These are the '' focal points'', the principal points, and the nodal points. For ''ideal'' ...
array box beneath the primary reflectors. The receivers are polarization-sensitive differential
radiometer A radiometer or roentgenometer is a device for measuring the radiant flux (power) of electromagnetic radiation. Generally, a radiometer is an infrared radiation detector or an ultraviolet detector. Microwave radiometers operate in the microwave ...
s measuring the difference between two telescope beams. The signal is amplified with High-electron-mobility transistor (HEMT)
low-noise amplifier A low-noise amplifier (LNA) is an electronic amplifier that amplifies a very low-power signal without significantly degrading its signal-to-noise ratio. An amplifier will increase the power of both the signal and the noise present at its input, ...
s, built by the
National Radio Astronomy Observatory The National Radio Astronomy Observatory (NRAO) is a federally funded research and development center of the United States National Science Foundation operated under cooperative agreement by Associated Universities, Inc. for the purpose of radio a ...
(NRAO). 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 An azimuth (; from ar, اَلسُّمُوت, as-sumūt, the directions) is an angular measurement in a spherical coordinate system. More specifically, it is the horizontal angle from a cardinal direction, most commonly north. Mathematical ...
is 180°; the total angle is 141°. To improve subtraction of foreground signals from our
Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. ...
galaxy, the WMAP used five discrete radio frequency bands, from 23 GHz to 94 GHz. The WMAP's base is a -diameter
solar panel A solar cell panel, solar electric panel, photo-voltaic (PV) module, PV panel or solar panel is an assembly of photovoltaic solar cells mounted in a (usually rectangular) frame, and a neatly organised collection of PV panels is called a photo ...
array that keeps the instruments in shadow during CMB observations, (by keeping the craft constantly angled at 22°, 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, -long thermal isolation shell atop the deck. Passive thermal radiators cool the WMAP to approximately ; they are connected to the
low-noise amplifier A low-noise amplifier (LNA) is an electronic amplifier that amplifies a very low-power signal without significantly degrading its signal-to-noise ratio. An amplifier will increase the power of both the signal and the noise present at its input, ...
s. 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. The WMAP's calibration is effected with the CMB dipole and measurements of
Jupiter Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousand ...
; the beam patterns are measured against Jupiter. The telescope's data are relayed daily via a 2-GHz transponder providing a 667 kbit/s downlink to a Deep Space Network station. The spacecraft has two transponders, one a redundant backup; they are minimally active – about 40 minutes daily – to minimize radio frequency interference. The telescope's position is maintained, in its three axes, with three
reaction wheel A reaction wheel (RW) is used primarily by spacecraft for three-axis attitude control, and does not require rockets or external applicators of torque. They provide a high pointing accuracy, and are particularly useful when the spacecraft must be ...
s,
gyroscope A gyroscope (from Ancient Greek γῦρος ''gŷros'', "round" and σκοπέω ''skopéō'', "to look") is a device used for measuring or maintaining orientation and angular velocity. It is a spinning wheel or disc in which the axis of rot ...
s, two star trackers and sun sensors, and is steered with eight
hydrazine Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...
thrusters.


Launch, trajectory, and orbit

The WMAP spacecraft arrived at the
Kennedy Space Center The John F. Kennedy Space Center (KSC, originally known as the NASA Launch Operations Center), located on Merritt Island, Florida, is one of the National Aeronautics and Space Administration's (NASA) ten field centers. Since December 196 ...
on 20 April 2001. After being tested for two months, it was launched via
Delta II Delta II was an expendable launch system, originally designed and built by McDonnell Douglas. Delta II was part of the Delta rocket family and entered service in 1989. Delta II vehicles included the Delta 6000, and the two later Delta 7000 va ...
7425 launch vehicle on 30 June 2001. 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 2 July 2001, it began working, first with in-flight testing (from launching until 17 August 2001), then began constant, formal work. Afterwards, it effected three Earth-Moon phase loops, measuring its
sidelobe In antenna engineering, sidelobes are the lobes (local maxima) of the far field radiation pattern of an antenna or other radiation source, that are not the '' main lobe''. The radiation pattern of most antennas shows a pattern of "''lobe ...
s, then flew by the Moon on 30 July 2001, en route to the Sun-Earth
Lagrange point In celestial mechanics, the Lagrange points (; also Lagrangian points or libration points) are points of equilibrium for small-mass objects under the influence of two massive orbiting bodies. Mathematically, this involves the solution of t ...
, arriving there on 1 October 2001, becoming the first CMB observation mission posted there. Locating the spacecraft at Lagrange 2, ( 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 in a
Lissajous orbit In orbital mechanics, a Lissajous orbit (), named after Jules Antoine Lissajous, is a quasi-periodic orbital trajectory that an object can follow around a Lagrangian point of a three-body system without requiring any propulsion. Lyapunov orbi ...
ca. 1.0° to 10°, with a 6-month period. The telescope rotates once every 2 minutes 9 seconds (0.464 rpm) and precesses at the rate of 1 revolution per hour. WMAP measured the entire sky every six months, and completed its first, full-sky observation in April 2002. File:WMAP launch.jpg, WMAP launches from
Kennedy Space Center The John F. Kennedy Space Center (KSC, originally known as the NASA Launch Operations Center), located on Merritt Island, Florida, is one of the National Aeronautics and Space Administration's (NASA) ten field centers. Since December 196 ...
, 30 June 2001 File:WMAP trajectory and orbit.jpg, The WMAP's trajectory and orbit File:WMAP orbit.jpg, WMAP's orbit and sky scan strategy


Experiment


Pseudo-Correlation Radiometer

The WMAP instrument consists of pseudo-correlation differential radiometers fed by two back-to-back primary Gregorian reflectors. This instrument uses five frequency bands from 22 GHz to 90 GHz to facilitate rejection of foreground signals from our own Galaxy. The WMAP instrument has a 3.5° x 3.5°
field of view The field of view (FoV) is the extent of the observable world that is seen at any given moment. In the case of optical instruments or sensors it is a solid angle through which a detector is sensitive to electromagnetic radiation. Human ...
(FoV).


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 Synchrotron radiation (also known as magnetobremsstrahlung radiation) is the electromagnetic radiation emitted when relativistic charged particles are subject to an acceleration perpendicular to their velocity (). It is produced artificially in ...
and
free-free emission ''Bremsstrahlung'' (), from "to brake" and "radiation"; i.e., "braking radiation" or "deceleration radiation", is electromagnetic radiation produced by the deceleration of a charged particle when deflected by another charged particle, typica ...
(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. 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.


Measurements and discoveries


One-year data release

On 11 February 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. Based upon the
Lambda-CDM model The ΛCDM (Lambda cold dark matter) or Lambda-CDM model is a parameterization of the Big Bang cosmological model in which the universe contains three major components: first, a cosmological constant denoted by Lambda ( Greek Λ) associated ...
, 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 In astronomy, the 2dF Galaxy Redshift Survey (Two-degree-Field Galaxy Redshift Survey), 2dF or 2dFGRS is a redshift survey conducted by the Australian Astronomical Observatory (AAO) with the 3.9m Anglo-Australian Telescope between 1997 and 11 A ...
and Lyman alpha forest measurements. There are degenerations among the parameters, the most significant is between n_s and \tau; the errors given are at 68% confidence. Using the best-fit data and theoretical models, the WMAP team determined the times of important universal events, including the redshift of reionization, ; the redshift of decoupling, (and the universe's age at decoupling, ); and the redshift of matter/radiation equality, . They determined the thickness of the surface of last scattering to be in redshift, or . They determined the current density of
baryon In particle physics, a baryon is a type of composite subatomic particle which contains an odd number of valence quarks (at least 3). Baryons belong to the hadron family of particles; hadrons are composed of quarks. Baryons are also classifie ...
s, , and the ratio of baryons to photons, . The WMAP's detection of an early reionization excluded
warm dark matter Warm dark matter (WDM) is a hypothesized form of dark matter that has properties intermediate between those of hot dark matter and cold dark matter, causing structure formation to occur bottom-up from above their free-streaming scale, and top-down ...
. The team also examined Milky Way emissions at the WMAP frequencies, producing a 208- point source catalogue.


Three-year data release

The three-year WMAP data were released on 17 March 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 In economics, inflation is an increase in the general price level of goods and services in an economy. When the general price level rises, each unit of currency buys fewer goods and services; consequently, inflation corresponds to a reduct ...
. The 3-year WMAP data alone shows that the universe must have
dark matter Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not ...
. Results were computed both only using WMAP data, and also with a mix of parameter constraints from other instruments, including other CMB experiments (
Arcminute Cosmology Bolometer Array Receiver ACBAR was an experiment to measure the anisotropy of the Cosmic microwave background. It was active 2000-2008. The ACBAR 145 GHz measurements were the most precise high multipole measurements of the CMB at the time. See also * Cosmic microw ...
(ACBAR),
Cosmic Background Imager The Cosmic Background Imager (or CBI) was a 13-element interferometer perched at an elevation of 5,080 metres (16,700 feet) at Llano de Chajnantor Observatory in the Chilean Andes. It started operations in 1999 to study the cosmic microwave bac ...
(CBI) and BOOMERANG),
Sloan Digital Sky Survey The Sloan Digital Sky Survey or SDSS is a major multi-spectral imaging and spectroscopic redshift survey using a dedicated 2.5-m wide-angle optical telescope at Apache Point Observatory in New Mexico, United States. The project began in 2000 ...
(SDSS), the
2dF Galaxy Redshift Survey In astronomy, the 2dF Galaxy Redshift Survey (Two-degree-Field Galaxy Redshift Survey), 2dF or 2dFGRS is a redshift survey conducted by the Australian Astronomical Observatory (AAO) with the 3.9m Anglo-Australian Telescope between 1997 and 11 A ...
, the
Supernova Legacy Survey The Supernova Legacy Survey Program is a project designed to investigate dark energy, by detecting and monitoring approximately 2000 high-redshift supernovae between 2003 and 2008, using MegaPrime, a large CCD mosaic at the Canada-France-Hawaii ...
and constraints on the
Hubble constant Hubble's law, also known as the Hubble–Lemaître law, is the observation in physical cosmology that galaxies are moving away from Earth at speeds proportional to their distance. In other words, the farther they are, the faster they are moving ...
from the
Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most vers ...
. Optical depth to reionization improved due to polarization measurements.Hinshaw et al. (2007)
<0.30 when combined with SDSS data. No indication of non-gaussianity.


Five-year data release

The five-year WMAP data were released on 28 February 2008. The data included new evidence for the
cosmic neutrino background The cosmic neutrino background (CNB or CB) is the universe's background particle radiation composed of neutrinos. They are sometimes known as relic neutrinos. The CB is a relic of the Big Bang; while the cosmic microwave background radiation ( ...
, evidence that it took over half billion years for the first stars to reionize the universe, and new constraints on
cosmic inflation In physical cosmology, cosmic inflation, cosmological inflation, or just inflation, is a theory of exponential expansion of space in the early universe. The inflationary epoch lasted from  seconds after the conjectured Big Bang singular ...
. The improvement in the results came from both having an extra 2 years of measurements (the data set runs between midnight on 10 August 2001 to midnight of 9 August 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. Improvements to the spectra were in the 3rd acoustic peak, and the polarization spectra. 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 In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales. The first observational evidence for its existence came from measurements of supernovas, which showed that the univ ...
at the time was negligible. It also constrained the content of the present-day universe; 4.6% atoms, 23% dark matter and 72% dark energy. The WMAP five-year data was combined with measurements from
Type Ia supernova A Type Ia supernova (read: "type one-A") is a type of supernova that occurs in binary systems (two stars orbiting one another) in which one of the stars is a white dwarf. The other star can be anything from a giant star to an even smaller white ...
(SNe) and
Baryon acoustic oscillations In cosmology, baryon acoustic oscillations (BAO) are fluctuations in the density of the visible baryonic matter (normal matter) of the universe, caused by acoustic density waves in the primordial plasma of the early universe. In the same way t ...
(BAO). The elliptical shape of the WMAP skymap is the result of a Mollweide projection.WMAP 1-year Paper Figures
Bennett, et al.
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 , the redshift of decoupling, (as well as age of universe at decoupling, ) and the redshift of matter/radiation equality, . The extragalactic source catalogue was expanded to include 390 sources, and variability was detected in the emission from
Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...
and
Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...
.


Seven-year data release

The seven-year WMAP data were released on 26 January 2010. As part of this release, claims for inconsistencies with the standard model were investigated. 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%).


Nine-year data release

On 29 December 2012, the nine-year WMAP data and related images were released. billion-year-old temperature fluctuations and a temperature range of ± 200 micro
kelvin The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based engineer and ...
s are shown in the image. In addition, the study found that 95% of the early universe is composed of
dark matter Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not ...
and
dark energy In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales. The first observational evidence for its existence came from measurements of supernovas, which showed that the univ ...
, the curvature of space is less than 0.4% of "flat" and the universe emerged from the cosmic Dark Ages "about 400 million years" after the
Big Bang The Big Bang event is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological models of the Big Bang explain the evolution of the observable universe from the ...
.Hinshaw, et al., 2013
/ref>


Main result

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 In physics, Planck's law describes the spectral density of electromagnetic radiation emitted by a black body in thermal equilibrium at a given temperature , when there is no net flow of matter or energy between the body and its environment. At ...
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 The Big Bang event is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological models of the Big Bang explain the evolution of the observable universe from the ...
, 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 ). 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 and in October 2010 the spacecraft was moved to a heliocentric "graveyard" orbit. 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
The E and B Experiment The E and B Experiment (EBEX) will measure the cosmic microwave background radiation of a part of the sky during two sub-orbital (high-altitude) balloon flights. It is an experiment to make large, high-fidelity images of the CMB polarization aniso ...
(EBEX),
Spider Spiders (order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species ...
, BICEP and Keck Array (BICEP2), Keck, QUIET, Cosmology Large Angular Scale Surveyor (CLASS),
South Pole Telescope The South Pole Telescope (SPT) is a diameter telescope located at the Amundsen–Scott South Pole Station, Antarctica. The telescope is designed for observations in the microwave, millimeter-wave, and submillimeter-wave regions of the electroma ...
(SPTpol) and others. On 21 March 2013, the European-led research team behind the Planck spacecraft released the mission's all-sky map of the cosmic microwave background. The map suggests the
universe The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development of the univers ...
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 Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not ...
. Based on the 2013 data, the universe contains 4.9% ordinary matter, 26.8%
dark matter Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not ...
and 68.3%
dark energy In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales. The first observational evidence for its existence came from measurements of supernovas, which showed that the univ ...
. 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 and the Hubble constant is 67.74 ± 0.46 (km/s)/Mpc.


See also

* Explorer program * Illustris project * List of cosmic microwave background experiments * List of cosmological computation software *
S150 Galactic X-Ray Mapping Skylab 3 (also SL-3 and SLM-2) was the second crewed mission to the first American space station, Skylab. The mission began on July 28, 1973, with the launch of NASA astronauts Alan Bean, Owen Garriott, and Jack Lousma in the Apollo command an ...


References


Primary sources

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Further reading

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External links


Sizing up the universe

Big Bang glow hints at funnel-shaped Universe
New Scientist ''New Scientist'' is a magazine covering all aspects of science and technology. Based in London, it publishes weekly English-language editions in the United Kingdom, the United States and Australia. An editorially separate organisation publish ...
, 15 April 2004
NASA 16 March 2006 WMAP inflation related press release
* {{Authority control Articles containing video clips Artificial satellites at Earth-Sun Lagrange points Cosmic microwave background experiments Derelict satellites in heliocentric orbit Explorers Program NASA space probes Space probes launched in 2001 Space telescopes Spacecraft launched by Delta II rockets Spacecraft using Lissajous orbits