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97-652: The Local Void is a vast, empty region of space , lying adjacent to the Local Group . Discovered by Brent Tully and Rick Fisher in 1987, the Local Void is now known to be composed of three separate sectors, separated by bridges of "wispy filaments ". The precise extent of the void is unknown, but it is at least 45  Mpc (150 million light-years ) across, and possibly 150 to 300 Mpc. The Local Void appears to have significantly fewer galaxies than expected from standard cosmology . Voids are affected by

194-587: A Dicke radiometer that they intended to use for radio astronomy and satellite communication experiments. The antenna was constructed in 1959 to support Project Echo —the National Aeronautics and Space Administration's passive communications satellites, which used large earth orbiting aluminized plastic balloons as reflectors to bounce radio signals from one point on the Earth to another. On 20 May 1964 they made their first measurement clearly showing

291-515: A brief paper by Soviet astrophysicists A. G. Doroshkevich and Igor Novikov , in the spring of 1964. In 1964, David Todd Wilkinson and Peter Roll, Dicke's colleagues at Princeton University , began constructing a Dicke radiometer to measure the cosmic microwave background. In 1964, Arno Penzias and Robert Woodrow Wilson at the Crawford Hill location of Bell Telephone Laboratories in nearby Holmdel Township, New Jersey had built

388-412: A factor of 10 less strong than the temperature anisotropy; it supplements the temperature data as they are correlated. The B-mode signal is even weaker but may contain additional cosmological data. The anisotropy is related to physical origin of the polarization. Excitation of an electron by linear polarized light generates polarized light at 90 degrees to the incident direction. If the incoming radiation

485-605: A heterogeneous plasma. E-modes were first seen in 2002 by the Degree Angular Scale Interferometer (DASI). B-modes are expected to be an order of magnitude weaker than the E-modes. The former are not produced by standard scalar type perturbations, but are generated by gravitational waves during cosmic inflation shortly after the big bang. However, gravitational lensing of the stronger E-modes can also produce B-mode polarization. Detecting

582-432: A larger void where matter is rushing away. The Local Void is surrounded uniformly by matter in all directions, except for one sector in which there is nothing, which has the effect of taking more matter away from that sector. The effect on the nearby galaxy is astonishingly large. The Milky Way's velocity away from the Local Void is 970,000 kilometres per hour (600,000 mph). Several void galaxies have been found within

679-578: A magnetic field of strength at least 10 G . The specific large-scale magnetic structure of the universe suggests primordial "magnetogenesis", which in turn could have played a role in the formation of magnetic fields within galaxies, and could also change estimates of the timeline of recombination in the early universe. Cold spots in the cosmic microwave background , such as the WMAP cold spot found by Wilkinson Microwave Anisotropy Probe , could possibly be explained by an extremely large cosmic void that has

776-406: A measured brightness temperature at any wavelength can be converted to a blackbody temperature. The radiation is remarkably uniform across the sky, very unlike the almost point-like structure of stars or clumps of stars in galaxies. The radiation is isotropic to roughly one part in 25,000: the root mean square variations are just over 100 μK, after subtracting a dipole anisotropy from

873-481: A radius of ~120 Mpc, as long as the late integrated Sachs–Wolfe effect was accounted for in the possible solution. Anomalies in CMB screenings are now being potentially explained through the existence of large voids located down the line-of-sight in which the cold spots lie. Although dark energy is currently the most popular explanation for the acceleration in the expansion of the universe , another theory elaborates on

970-515: A series of peaks whose angular scales ( ℓ values of the peaks) are roughly in the ratio 1 : 3 : 5 : ..., while adiabatic density perturbations produce peaks whose locations are in the ratio 1 : 2 : 3 : ... Observations are consistent with the primordial density perturbations being entirely adiabatic, providing key support for inflation, and ruling out many models of structure formation involving, for example, cosmic strings. Collisionless damping

1067-404: A thermal spectrum. The cosmic microwave background was first predicted in 1948 by Ralph Alpher and Robert Herman , in a correction they prepared for a paper by Alpher's PhD advisor George Gamow . Alpher and Herman were able to estimate the temperature of the cosmic microwave background to be 5 K. The first published recognition of the CMB radiation as a detectable phenomenon appeared in

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1164-610: Is flat . A number of ground-based interferometers provided measurements of the fluctuations with higher accuracy over the next three years, including the Very Small Array , Degree Angular Scale Interferometer (DASI), and the Cosmic Background Imager (CBI). DASI made the first detection of the polarization of the CMB and the CBI provided the first E-mode polarization spectrum with compelling evidence that it

1261-412: Is microwave radiation that fills all space in the observable universe . With a standard optical telescope , the background space between stars and galaxies is almost completely dark. However, a sufficiently sensitive radio telescope detects a faint background glow that is almost uniform and is not associated with any star, galaxy, or other object . This glow is strongest in the microwave region of

1358-476: Is an emission of uniform black body thermal energy coming from all directions. Intensity of the CMB is expressed in kelvin (K), the SI unit of temperature. The CMB has a thermal black body spectrum at a temperature of 2.725 48 ± 0.000 57  K . Variations in intensity are expressed as variations in temperature. The blackbody temperature uniquely characterizes the intensity of the radiation at all wavelengths;

1455-525: Is caused by two effects, when the treatment of the primordial plasma as fluid begins to break down: These effects contribute about equally to the suppression of anisotropies at small scales and give rise to the characteristic exponential damping tail seen in the very small angular scale anisotropies. The depth of the LSS refers to the fact that the decoupling of the photons and baryons does not happen instantaneously, but instead requires an appreciable fraction of

1552-405: Is determined by various interactions of matter and photons up to the point of decoupling, which results in a characteristic lumpy pattern that varies with angular scale. The distribution of the anisotropy across the sky has frequency components that can be represented by a power spectrum displaying a sequence of peaks and valleys. The peak values of this spectrum hold important information about

1649-461: Is drastically different from the previous two algorithms listed. The most striking aspect is that it requires a different definition of what it means to be a void. Instead of the general notion that a void is a region of space with a low cosmic mean density; a hole in the distribution of galaxies, it defines voids to be regions in which matter is escaping; which corresponds to the dark energy equation of state, w . Void centers are then considered to be

1746-463: Is in a cosmic void named the KBC Void . Some popular applications are mentioned in detail below. The simultaneous existence of the largest-known voids and galaxy clusters requires about 70% dark energy in the universe today, consistent with the latest data from the cosmic microwave background. Voids act as bubbles in the universe that are sensitive to background cosmological changes. This means that

1843-414: Is isotropic, different incoming directions create polarizations that cancel out. If the incoming radiation has quadrupole anisotropy, residual polarization will be seen. Other than the temperature and polarization anisotropy, the CMB frequency spectrum is expected to feature tiny departures from the black-body law known as spectral distortions . These are also at the focus of an active research effort with

1940-591: Is known quite precisely. The first-year WMAP results put the time at which P ( t ) has a maximum as 372,000 years. This is often taken as the "time" at which the CMB formed. However, to figure out how long it took the photons and baryons to decouple, we need a measure of the width of the PVF. The WMAP team finds that the PVF is greater than half of its maximal value (the "full width at half maximum", or FWHM) over an interval of 115,000 years. By this measure, decoupling took place over roughly 115,000 years, and thus when it

2037-474: Is no single agreed-upon definition of what constitutes a void. The matter density value used for describing the cosmic mean density is usually based on a ratio of the number of galaxies per unit volume rather than the total mass of the matter contained in a unit volume. Study of cosmic voids within the discipline of astrophysics began in the mid-1970s when redshift surveys led two separate teams of astrophysicists in 1978 to identify superclusters and voids in

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2134-466: Is out of phase with the T-mode spectrum. In June 2001, NASA launched a second CMB space mission, WMAP , to make much more precise measurements of the large scale anisotropies over the full sky. WMAP used symmetric, rapid-multi-modulated scanning, rapid switching radiometers at five frequencies to minimize non-sky signal noise. The data from the mission was released in five installments, the last being

2231-467: Is significant in providing physical evidence for dark energy. The structure of the Universe can be broken down into components that can help describe the characteristics of individual regions of the cosmos. These are the main structural components of the cosmic web: Voids have a mean density less than a tenth of the average density of the universe. This serves as a working definition even though there

2328-590: Is similar in design to the Cosmic Background Imager (CBI) and the Very Small Array (VSA). A third space mission, the ESA (European Space Agency) Planck Surveyor , was launched in May 2009 and performed an even more detailed investigation until it was shut down in October 2013. Planck employed both HEMT radiometers and bolometer technology and measured the CMB at a smaller scale than WMAP. Its detectors were trialled in

2425-449: Is still a matter of scientific debate. It may have included starlight from the very first population of stars ( population III stars), supernovae when these first stars reached the end of their lives, or the ionizing radiation produced by the accretion disks of massive black holes. The time following the emission of the cosmic microwave background—and before the observation of the first stars—is semi-humorously referred to by cosmologists as

2522-476: Is that the resulting voids from this method are intrinsically different than those found by other methods, which makes an all-data points inclusive comparison between results of differing algorithms very difficult. Voids have contributed significantly to the modern understanding of the cosmos, with applications ranging from shedding light on the current understanding of dark energy , to refining and constraining cosmological evolution models. The Milky Way Galaxy

2619-402: Is that voids have been shown to contain a significantly higher fraction of starburst galaxies of young, hot stars when compared to samples of galaxies in walls. Voids offer opportunities to study the strength of intergalactic magnetic fields. For example, a 2015 study concluded, based on the deflection of blazar gamma-ray emissions that travel through voids, that intergalactic space contains

2716-576: The Big Bang , collapses of mass followed by implosions of the compressed baryonic matter . Starting from initially small anisotropies from quantum fluctuations in the early universe, the anisotropies grew larger in scale over time. Regions of higher density collapsed more rapidly under gravity, eventually resulting in the large-scale, foam-like structure or "cosmic web" of voids and galaxy filaments seen today. Voids located in high-density environments are smaller than voids situated in low-density spaces of

2813-530: The Dark Age , and is a period which is under intense study by astronomers (see 21 centimeter radiation ). Two other effects which occurred between reionization and our observations of the cosmic microwave background, and which appear to cause anisotropies, are the Sunyaev–Zeldovich effect , where a cloud of high-energy electrons scatters the radiation, transferring some of its energy to the CMB photons, and

2910-502: The Doppler shift of the background radiation. The latter is caused by the peculiar velocity of the Sun relative to the comoving cosmic rest frame as it moves at 369.82 ± 0.11 km/s towards the constellation Crater near its boundary with the constellation Leo The CMB dipole and aberration at higher multipoles have been measured, consistent with galactic motion. Despite

3007-556: The Euclid satellite ) to measure the sum of the masses of all neutrino species by comparing the statistical properties of void samples to theoretical predictions. Cosmic voids contain a mix of galaxies and matter that is slightly different than other regions in the universe. This unique mix supports the biased galaxy formation picture predicted in Gaussian adiabatic cold dark matter models. This phenomenon provides an opportunity to modify

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3104-734: The Sachs–Wolfe effect , which causes photons from the Cosmic Microwave Background to be gravitationally redshifted or blueshifted due to changing gravitational fields. The standard cosmology that includes the Big Bang "enjoys considerable popularity among the practicing cosmologists" However, there are challenges to the standard big bang framework for explaining CMB data. In particular standard cosmology requires fine-tuning of some free parameters, with different values supported by different experimental data. As an example of

3201-519: The cosmological redshift associated with the expansion of the universe . The surface of last scattering refers to a shell at the right distance in space so photons are now received that were originally emitted at the time of decoupling. The CMB is not completely smooth and uniform, showing a faint anisotropy that can be mapped by sensitive detectors. Ground and space-based experiments such as COBE , WMAP and Planck have been used to measure these temperature inhomogeneities. The anisotropy structure

3298-550: The expansion of the universe according to Hubble's law . A summarized timeline of important events in the field of cosmic voids from its beginning to recent times is as follows: There exist a number of ways for finding voids with the results of large-scale surveys of the universe. Of the many different algorithms, virtually all fall into one of three general categories. The first class consists of void finders that try to find empty regions of space based on local galaxy density. The second class are those which try to find voids via

3395-551: The inflaton field that caused the inflation event. Long before the formation of stars and planets, the early universe was more compact, much hotter and, starting 10 seconds after the Big Bang, filled with a uniform glow from its white-hot fog of interacting plasma of photons , electrons , and baryons . As the universe expanded , adiabatic cooling caused the energy density of the plasma to decrease until it became favorable for electrons to combine with protons , forming hydrogen atoms. This recombination event happened when

3492-437: The photon – baryon plasma in the early universe. The pressure of the photons tends to erase anisotropies, whereas the gravitational attraction of the baryons, moving at speeds much slower than light, makes them tend to collapse to form overdensities. These two effects compete to create acoustic oscillations, which give the microwave background its characteristic peak structure. The peaks correspond, roughly, to resonances in which

3589-461: The two decades. The sensitivity of the new experiments improved dramatically, with a reduction in internal noise by three orders of magnitude. The primary goal of these experiments was to measure the scale of the first acoustic peak, which COBE did not have sufficient resolution to resolve. This peak corresponds to large scale density variations in the early universe that are created by gravitational instabilities, resulting in acoustical oscillations in

3686-458: The 1970s numerous studies showed that tiny deviations from isotropy in the CMB could result from events in the early universe. Harrison, Peebles and Yu, and Zel'dovich realized that the early universe would require quantum inhomogeneities that would result in temperature anisotropy at the level of 10 or 10 . Rashid Sunyaev , using the alternative name relic radiation , calculated the observable imprint that these inhomogeneities would have on

3783-454: The 1978 Nobel Prize in Physics for their discovery. The interpretation of the cosmic microwave background was a controversial issue in the late 1960s. Alternative explanations included energy from within the solar system, from galaxies, from intergalactic plasma and from multiple extragalactic radio sources. Two requirements would show that the microwave radiation was truly "cosmic". First,

3880-555: 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 . The cosmic microwave background radiation and the cosmological redshift -distance relation are together regarded as

3977-667: The Antarctic Viper telescope as ACBAR ( Arcminute Cosmology Bolometer Array Receiver ) experiment—which has produced the most precise measurements at small angular scales to date—and in the Archeops balloon telescope. On 21 March 2013, the European-led research team behind the Planck cosmology probe released the mission's all-sky map ( 565x318 jpeg , 3600x1800 jpeg ) of the cosmic microwave background. The map suggests

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4074-409: The CMB as a function of redshift, z , can be shown to be proportional to the color temperature of the CMB as observed in the present day (2.725 K or 0.2348 meV): The high degree of uniformity throughout the observable universe and its faint but measured anisotropy lend strong support for the Big Bang model in general and the ΛCDM ("Lambda Cold Dark Matter") model in particular. Moreover,

4171-462: The Local Void or Local Hole. Some media reports have dubbed it the KBC Void , although this name has not been taken up in other publications. Scientists believe that the Local Void is growing and that the Local Sheet , which makes up one wall of the void, is rushing away from the void's centre at 260 kilometres per second (160 mi/s). Concentrations of matter normally pull together, creating

4268-566: The Local Void. These include: Void (astronomy) Voids typically have a diameter of 10 to 100 megaparsecs (30 to 300 million light-years ); particularly large voids, defined by the absence of rich superclusters , are sometimes called supervoids . They were first discovered in 1978 in a pioneering study by Stephen Gregory and Laird A. Thompson at the Kitt Peak National Observatory . Voids are believed to have been formed by baryon acoustic oscillations in

4365-553: The Nearest Neighbor Approximation to calculate the cosmic density in the region contained in a spherical radius determined by the distance to the third-closest galaxy. El Ad & Piran introduced this method in 1997 to allow a quick and effective method for standardizing the cataloging of voids. Once the spherical cells are mined from all of the structure data, each cell is expanded until the underdensity returns to average expected wall density values. One of

4462-474: The abundance of clusters of galaxies, is a promising method for precision tests of deviations from general relativity on large scales and in low-density regions. The insides of voids often seem to adhere to cosmological parameters which differ from those of the known universe . It is because of this unique feature that cosmic voids are useful laboratories to study the effects that gravitational clustering and growth rates have on local galaxies and structure when

4559-415: The abundance of voids is a promising way to constrain the dark energy equation of state. Neutrinos, due to their very small mass and extremely weak interaction with other matter, will free-stream in and out of voids which are smaller than the mean-free path of neutrinos. This has an effect on the size and depth distribution of voids, and is expected to make it possible with future astronomical surveys (e.g.

4656-417: The age of the universe up to that era. One method of quantifying how long this process took uses the photon visibility function (PVF). This function is defined so that, denoting the PVF by P ( t ), the probability that a CMB photon last scattered between time t and t + dt is given by P ( t )   dt . The maximum of the PVF (the time when it is most likely that a given CMB photon last scattered)

4753-432: The algorithm places a statistical significance on each void it finds. A physical significance parameter can be applied in order to reduce the number of trivial voids by including a minimum density to average density ratio of at least 1:5. Subvoids are also identified using this process which raises more philosophical questions on what qualifies as a void. Void finders such as VIDE are based on ZOBOV. This third-class method

4850-484: The anisotropies in the cosmic microwave background. The CMB spectrum has become the most precisely measured black body spectrum in nature. In the late 1940s Alpher and Herman reasoned that if there was a Big Bang, the expansion of the universe would have stretched the high-energy radiation of the very early universe into the microwave region of the electromagnetic spectrum , and down to a temperature of about 5 K. They were slightly off with their estimate, but they had

4947-408: The background radiation with intervening hot gas or gravitational potentials, which occur between the last scattering surface and the observer. The structure of the cosmic microwave background anisotropies is principally determined by two effects: acoustic oscillations and diffusion damping (also called collisionless damping or Silk damping). The acoustic oscillations arise because of a conflict in

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5044-642: The best available evidence for the Big Bang event. Measurements of the CMB have made the inflationary Big Bang model the Standard Cosmological Model . The discovery of the CMB in the mid-1960s curtailed interest in alternatives such as the steady state theory . In the Big Bang model for the formation of the universe , inflationary cosmology predicts that after about 10 seconds the nascent universe underwent exponential growth that smoothed out nearly all irregularities. The remaining irregularities were caused by quantum fluctuations in

5141-399: The catalog had a minimum radius of 10 Mpc in order to ensure all identified voids were not accidentally cataloged due to sampling errors. This particular second-class algorithm uses a Voronoi tessellation technique and mock border particles in order to categorize regions based on a high-density contrasting border with a very low amount of bias. Neyrinck introduced this algorithm in 2008 with

5238-443: The classification of three distinct types of voids. These three morphological classes are True voids, Pancake voids, and Filament voids. Another notable quality is that even though DIVA also contains selection function bias just as first-class methods do, DIVA is devised such that this bias can be precisely calibrated, leading to much more reliable results. Multiple shortfalls of this Lagrangian-Eulerian hybrid approach exist. One example

5335-439: The color temperature of the background radiation has dropped by an average factor of 1,089 due to the expansion of the universe. As the universe expands, the CMB photons are redshifted , causing them to decrease in energy. The color temperature of this radiation stays inversely proportional to a parameter that describes the relative expansion of the universe over time, known as the scale length . The color temperature T r of

5432-478: The cosmic microwave background. After a lull in the 1970s caused in part by the many experimental difficulties in measuring CMB at high precision, increasingly stringent limits on the anisotropy of the cosmic microwave background were set by ground-based experiments during the 1980s. RELIKT-1 , a Soviet cosmic microwave background anisotropy experiment on board the Prognoz 9 satellite (launched 1 July 1983), gave

5529-679: The cosmological parameters have different values from the outside universe. Due to the observation that larger voids predominantly remain in a linear regime, with most structures within exhibiting spherical symmetry in the underdense environment; that is, the underdensity leads to near-negligible particle-particle gravitational interactions that would otherwise occur in a region of normal galactic density. Testing models for voids can be performed with very high accuracy. The cosmological parameters that differ in these voids are Ω m , Ω Λ , and H 0 . Cosmic microwave background The cosmic microwave background ( CMB , CMBR ), or relic radiation ,

5626-458: The decoupling event is estimated to have occurred and at a point in time such that the photons from that distance have just reached observers. Most of the radiation energy in the universe is in the cosmic microwave background, making up a fraction of roughly 6 × 10 of the total density of the universe. Two of the greatest successes of the Big Bang theory are its prediction of the almost perfect black body spectrum and its detailed prediction of

5723-410: The distribution of galaxies and Abell clusters . The new redshift surveys revolutionized the field of astronomy by adding depth to the two-dimensional maps of cosmological structure, which were often densely packed and overlapping, allowing for the first three-dimensional mapping of the universe. Through redshift surveys, their depth was calculated from the individual redshifts of the galaxies due to

5820-535: The edge of the Local Group . It is believed that the distance from Earth to the centre of the Local Void must be at least 23 megaparsecs (75 Mly). The size of the Local Void was calculated due to an isolated dwarf galaxy known as ESO 461-36 located inside it. The bigger and emptier the void, the weaker its gravity, and the faster the dwarf should be fleeing the void towards concentrations of matter, yet discrepancies give room for competing theories. Dark energy has been suggested as one alternative explanation for

5917-448: The electromagnetic spectrum. The accidental discovery of the CMB in 1965 by American radio astronomers Arno Penzias and Robert Wilson was the culmination of work initiated in the 1940s. The CMB is landmark evidence of the Big Bang theory for the origin of the universe. In the Big Bang cosmological models , during the earliest periods, the universe was filled with an opaque fog of dense, hot plasma of sub-atomic particles . As

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6014-475: The evolution of a void's shape is in part the result of the expansion of the universe. Since this acceleration is believed to be caused by dark energy, studying the changes of a void's shape over a period of time can be used to constrain the standard Λ CDM model, or further refine the Quintessence + Cold Dark Matter ( QCDM ) model and provide a more accurate dark energy equation of state . Additionally

6111-594: The fine-tuning issue, standard cosmology cannot predict the present temperature of the relic radiation, T 0 {\displaystyle T_{0}} . This value of T 0 {\displaystyle T_{0}} is one of the best results of experimental cosmology and the steady state model can predict it. However, alternative models have their own set of problems and they have only made post-facto explanations of existing observations. Nevertheless, these alternatives have played an important historic role in providing ideas for and challenges to

6208-516: The first upper limits on the large-scale anisotropy. The other key event in the 1980s was the proposal by Alan Guth for cosmic inflation . This theory of rapid spatial expansion gave an explanation for large-scale isotropy by allowing causal connection just before the epoch of last scattering. With this and similar theories, detailed prediction encouraged larger and more ambitious experiments. The NASA Cosmic Background Explorer ( COBE ) satellite orbited Earth in 1989–1996 detected and quantified

6305-473: The fluctuations are coherent on angular scales that are larger than the apparent cosmological horizon at recombination. Either such coherence is acausally fine-tuned , or cosmic inflation occurred. The anisotropy , or directional dependency, of the cosmic microwave background is divided into two types: primary anisotropy, due to effects that occur at the surface of last scattering and before; and secondary anisotropy, due to effects such as interactions of

6402-413: The geometrical structures in the dark matter distribution as suggested by the galaxies. The third class is made of those finders which identify structures dynamically by using gravitationally unstable points in the distribution of dark matter. The three most popular methods through the study of cosmic voids are listed below. This first-class method uses each galaxy in a catalog as its target and then uses

6499-543: The helpful features of void regions is that their boundaries are very distinct and defined, with a cosmic mean density that starts at 10% in the body and quickly rises to 20% at the edge and then to 100% in the walls directly outside the edges. The remaining walls and overlapping void regions are then gridded into, respectively, distinct and intertwining zones of filaments, clusters, and near-empty voids. Any overlap of more than 10% with already known voids are considered to be subregions within those known voids. All voids admitted to

6596-411: The hope of a first measurement within the forthcoming decades, as they contain a wealth of information about the primordial universe and the formation of structures at late time. The CMB contains the vast majority of photons in the universe by a factor of 400 to 1; the number density of photons in the CMB is one billion times (10 ) the number density of matter in the universe. Without the expansion of

6693-406: The intensity vs frequency or spectrum needed to be shown to match a thermal or blackbody source. This was accomplished by 1968 in a series of measurements of the radiation temperature at higher and lower wavelengths. Second, the radiation needed be shown to be isotropic, the same from all directions. This was also accomplished by 1970, demonstrating that this radiation was truly cosmic in origin. In

6790-668: The large scale anisotropies at the limit of its detection capabilities. The NASA COBE mission clearly confirmed the primary anisotropy with the Differential Microwave Radiometer instrument, publishing their findings in 1992. The team received the Nobel Prize in physics for 2006 for this discovery. Inspired by the COBE results, a series of ground and balloon-based experiments measured cosmic microwave background anisotropies on smaller angular scales over

6887-460: The leading theory of cosmic structure formation, and suggested cosmic inflation was the right theory. During the 1990s, the first peak was measured with increasing sensitivity and by 2000 the BOOMERanG experiment reported that the highest power fluctuations occur at scales of approximately one degree. Together with other cosmological data, these results implied that the geometry of the universe

6984-421: The maximal source of the displacement field denoted as S ψ . The purpose for this change in definitions was presented by Lavaux and Wandelt in 2009 as a way to yield cosmic voids such that exact analytical calculations can be made on their dynamical and geometrical properties. This allows DIVA to heavily explore the ellipticity of voids and how they evolve in the large-scale structure, subsequently leading to

7081-399: The morphology-density correlation that holds discrepancies with these voids. Such observations like the morphology-density correlation can help uncover new facets about how galaxies form and evolve on the large scale. On a more local scale, galaxies that reside in voids have differing morphological and spectral properties than those that are located in the walls. One feature that has been found

7178-514: The nine year summary. The results are broadly consistent Lambda CDM models based on 6 free parameters and fitting in to Big Bang cosmology with cosmic inflation . 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 ( Ka band ) in ten bands. The instrument

7275-534: The peaks give important information about the nature of the primordial density perturbations. There are two fundamental types of density perturbations called adiabatic and isocurvature . A general density perturbation is a mixture of both, and different theories that purport to explain the primordial density perturbation spectrum predict different mixtures. The CMB spectrum can distinguish between these two because these two types of perturbations produce different peak locations. Isocurvature density perturbations produce

7372-435: The photons decouple when a particular mode is at its peak amplitude. The peaks contain interesting physical signatures. The angular scale of the first peak determines the curvature of the universe (but not the topology of the universe). The next peak—ratio of the odd peaks to the even peaks—determines the reduced baryon density. The third peak can be used to get information about the dark-matter density. The locations of

7469-426: The physical properties of the early universe: the first peak determines the overall curvature of the universe , while the second and third peak detail the density of normal matter and so-called dark matter , respectively. Extracting fine details from the CMB data can be challenging, since the emission has undergone modification by foreground features such as galaxy clusters . The cosmic microwave background radiation

7566-460: The plasma. The first peak in the anisotropy was tentatively detected by the MAT/TOCO experiment and the result was confirmed by the BOOMERanG and MAXIMA experiments. These measurements demonstrated that the geometry of the universe is approximately flat, rather than curved . They ruled out cosmic strings as a major component of cosmic structure formation and suggested cosmic inflation

7663-494: The possibility of our galaxy being part of a very large, not-so-underdense, cosmic void. According to this theory, such an environment could naively lead to the demand for dark energy to solve the problem with the observed acceleration. As more data has been released on this topic the chances of it being a realistic solution in place of the current Λ CDM interpretation has been largely diminished but not all together abandoned. The abundance of voids, particularly when combined with

7760-465: The presence of the microwave background, with their instrument having an excess 4.2K antenna temperature which they could not account for. After receiving a telephone call from Crawford Hill, Dicke said "Boys, we've been scooped." A meeting between the Princeton and Crawford Hill groups determined that the antenna temperature was indeed due to the microwave background. Penzias and Wilson received

7857-413: The purpose of introducing a method that did not contain free parameters or presumed shape tessellations. Therefore, this technique can create more accurately shaped and sized void regions. Although this algorithm has some advantages in shape and size, it has been criticized often for sometimes providing loosely defined results. Since it has no free parameters, it mostly finds small and trivial voids, although

7954-431: The right idea. They predicted the CMB. It took another 15 years for Penzias and Wilson to discover that the microwave background was actually there. According to standard cosmology, the CMB gives a snapshot of the hot early universe at the point in time when the temperature dropped enough to allow electrons and protons to form hydrogen atoms. This event made the universe nearly transparent to radiation because light

8051-511: The speedy expulsion of the dwarf galaxy. An earlier " Hubble Bubble " model, based on measured velocities of Type 1a supernovae , proposed a relative void centred on the Milky Way. Recent analysis of that data, however, suggested that interstellar dust had resulted in misleading measurements. Several authors have shown that the local universe up to 300 Mpc from the Milky Way is less dense than surrounding areas – by 15–50%. This has been called

8148-425: The standard explanation. The cosmic microwave background is polarized at the level of a few microkelvin. There are two types of polarization, called E-mode (or gradient-mode) and B-mode (or curl mode). This is in analogy to electrostatics , in which the electric field ( E -field) has a vanishing curl and the magnetic field ( B -field) has a vanishing divergence . The E-modes arise from Thomson scattering in

8245-444: The temperature was around 3000 K or when the universe was approximately 379,000 years old. As photons did not interact with these electrically neutral atoms, the former began to travel freely through space, resulting in the decoupling of matter and radiation. The color temperature of the ensemble of decoupled photons has continued to diminish ever since; now down to 2.7260 ± 0.0013 K , it will continue to drop as

8342-432: The universe expanded, this plasma cooled to the point where protons and electrons combined to form neutral atoms of mostly hydrogen. Unlike the plasma, these atoms could not scatter thermal radiation by Thomson scattering , and so the universe became transparent. Known as the recombination epoch, this decoupling event released photons to travel freely through space. However, the photons have grown less energetic due to

8439-407: The universe expands. The intensity of the radiation corresponds to black-body radiation at 2.726 K because red-shifted black-body radiation is just like black-body radiation at a lower temperature. According to the Big Bang model, the radiation from the sky we measure today comes from a spherical surface called the surface of last scattering . This represents the set of locations in space at which

8536-441: The universe is slightly older than researchers expected. 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 ) of a second. Apparently, these ripples gave rise to the present vast cosmic web of galaxy clusters and dark matter . Based on

8633-458: The universe to cause the cooling of the CMB, the night sky would shine as brightly as the Sun. The energy density of the CMB is 0.260 eV/cm (4.17 × 10  J/m ), about 411 photons/cm . In 1931, Georges Lemaître speculated that remnants of the early universe may be observable as radiation, but his candidate was cosmic rays . Richard C. Tolman showed in 1934 that expansion of the universe would cool blackbody radiation while maintaining

8730-458: The universe. Voids appear to correlate with the observed temperature of the cosmic microwave background (CMB) because of the Sachs–Wolfe effect . Colder regions correlate with voids, and hotter regions correlate with filaments because of gravitational redshifting . As the Sachs–Wolfe effect is only significant if the universe is dominated by radiation or dark energy , the existence of voids

8827-400: The very small degree of anisotropy in the CMB, many aspects can be measured with high precision and such measurements are critical for cosmological theories. In addition to temperature anisotropy, the CMB should have an angular variation in polarization . The polarization at each direction in the sky has an orientation described in terms of E-mode and B-mode polarization. The E-mode signal is

8924-544: The volume of the intergalactic medium (IGM) consists of ionized material (since there are few absorption lines due to hydrogen atoms). This implies a period of reionization during which some of the material of the universe was broken into hydrogen ions. The CMB photons are scattered by free charges such as electrons that are not bound in atoms. In an ionized universe, such charged particles have been liberated from neutral atoms by ionizing (ultraviolet) radiation. Today these free charges are at sufficiently low density in most of

9021-581: The volume of the universe that they do not measurably affect the CMB. However, if the IGM was ionized at very early times when the universe was still denser, then there are two main effects on the CMB: Both of these effects have been observed by the WMAP spacecraft, providing evidence that the universe was ionized at very early times, at a redshift around 10. The detailed provenance of this early ionizing radiation

9118-529: The way gravity causes matter in the universe to "clump together", herding galaxies into clusters and chains, which are separated by regions mostly devoid of galaxies, yet the exact mechanisms are subject to scientific debate. Astronomers have previously noticed that the Milky Way sits in a large, flat array of galaxies called the Local Sheet , which bounds the Local Void. The Local Void extends approximately 60 megaparsecs (200 Mly), beginning at

9215-470: Was complete, the universe was roughly 487,000 years old. Since the CMB came into existence, it has apparently been modified by several subsequent physical processes, which are collectively referred to as late-time anisotropy, or secondary anisotropy. When the CMB photons became free to travel unimpeded, ordinary matter in the universe was mostly in the form of neutral hydrogen and helium atoms. However, observations of galaxies today seem to indicate that most of

9312-440: Was no longer being scattered off free electrons. When this occurred some 380,000 years after the Big Bang, the temperature of the universe was about 3,000 K. This corresponds to an ambient energy of about 0.26  eV , which is much less than the 13.6 eV ionization energy of hydrogen. This epoch is generally known as the "time of last scattering" or the period of recombination or decoupling . Since decoupling,

9409-475: Was the right theory of structure formation. Inspired by the initial COBE results of an extremely isotropic and homogeneous background, a series of ground- and balloon-based experiments quantified CMB anisotropies on smaller angular scales over the next decade. The primary goal of these experiments was to measure the angular scale of the first acoustic peak, for which COBE did not have sufficient resolution. These measurements were able to rule out cosmic strings as

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