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124-555: The supercluster includes four large galaxy clusters in the Centaurus part, also known as the "4 clusters'' filament, or '' 4 clusters strand '': The filament which also includes the major cluster Abell S753 and exends up to around 260  Mly (80  Mpc ) to reach the rich galaxy cluster Abell 3581 . The Antlia Wall , also known as the Antlia Strand , Hydra Wall , Hydra-Antlia wall , Hydra-Antlia extension , and

248-414: A − 3 {\displaystyle \rho \propto a^{-3}} , where a {\displaystyle a} is the scale factor . For ultrarelativistic particles ("radiation"), the energy density drops more sharply, as ρ ∝ a − 4 {\displaystyle \rho \propto a^{-4}} . This is because in addition to the volume dilution of

372-548: A linear relationship between distance to galaxies and their recessional velocity . Edwin Hubble observationally confirmed Lundmark's and Lemaître's findings in 1929. Assuming the cosmological principle , these findings would imply that all galaxies are moving away from each other. Astronomer Walter Baade recalculated the size of the known universe in the 1940s, doubling the previous calculation made by Hubble in 1929. He announced this finding to considerable astonishment at

496-500: A concentration of mass equivalent to tens of thousands of galaxies. The Great Attractor, discovered in 1986, lies at a distance of between 150 million and 250 million light-years in the direction of the Hydra and Centaurus constellations . In its vicinity there is a preponderance of large old galaxies, many of which are colliding with their neighbours, or radiating large amounts of radio waves. In 1987, astronomer R. Brent Tully of

620-464: A distance ct in a time t , as the red worldline illustrates. While it always moves locally at  c , its time in transit (about 13 billion years) is not related to the distance traveled in any simple way, since the universe expands as the light beam traverses space and time. The distance traveled is thus inherently ambiguous because of the changing scale of the universe. Nevertheless, there are two distances that appear to be physically meaningful:

744-404: A finite distance. The comoving distance that such particles can have covered over the age of the universe is known as the particle horizon , and the region of the universe that lies within our particle horizon is known as the observable universe . If the dark energy that is inferred to dominate the universe today is a cosmological constant, then the particle horizon converges to a finite value in

868-550: A given comoving distance is defined to lie within the "observable universe" if we can receive signals emitted by the galaxy at any age in its history, say, a signal sent from the galaxy only 500 million years after the Big Bang. Because of the universe's expansion, there may be some later age at which a signal sent from the same galaxy can never reach the Earth at any point in the infinite future, so, for example, we might never see what

992-400: A higher-dimensional analogue of the 2D surface of a sphere that is finite in area but has no edge. It is plausible that the galaxies within the observable universe represent only a minuscule fraction of the galaxies in the universe. According to the theory of cosmic inflation initially introduced by Alan Guth and D. Kazanas , if it is assumed that inflation began about 10 seconds after

1116-435: A non-zero Riemann curvature tensor in curvature of Riemannian manifolds . Euclidean "geometrically flat" space has a Riemann curvature tensor of zero. "Geometrically flat" space has three dimensions and is consistent with Euclidean space. However, spacetime has four dimensions; it is not flat according to Einstein's general theory of relativity. Einstein's theory postulates that "matter and energy curve spacetime, and there

1240-490: A phenomenon that has been referred to as the End of Greatness . The organization of structure arguably begins at the stellar level, though most cosmologists rarely address astrophysics on that scale. Stars are organized into galaxies , which in turn form galaxy groups , galaxy clusters , superclusters , sheets, walls and filaments , which are separated by immense voids , creating a vast foam-like structure sometimes called

1364-433: A priori constraints) on how the space in which we live is connected or whether it wraps around on itself as a compact space . Though certain cosmological models such as Gödel's universe even permit bizarre worldlines that intersect with themselves, ultimately the question as to whether we are in something like a " Pac-Man universe", where if traveling far enough in one direction would allow one to simply end up back in

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1488-559: Is 4.8% of the total critical density or 4.08 × 10  kg/m . To convert this density to mass we must multiply by volume, a value based on the radius of the "observable universe". Since the universe has been expanding for 13.8 billion years, the comoving distance (radius) is now about 46.6 billion light-years. Thus, volume ( ⁠ 4 / 3 ⁠ πr ) equals 3.58 × 10  m and the mass of ordinary matter equals density ( 4.08 × 10  kg/m ) times volume ( 3.58 × 10  m ) or 1.46 × 10  kg . Sky surveys and mappings of

1612-458: Is a disagreement between this measurement and the supernova-based measurements, known as the Hubble tension . A third option proposed recently is to use information from gravitational wave events (especially those involving the merger of neutron stars , like GW170817 ), to measure the expansion rate. Such measurements do not yet have the precision to resolve the Hubble tension. In principle,

1736-503: Is a key feature of Big Bang cosmology. It can be modeled mathematically with the Friedmann–Lemaître–Robertson–Walker metric (FLRW), where it corresponds to an increase in the scale of the spatial part of the universe's spacetime metric tensor (which governs the size and geometry of spacetime). Within this framework, the separation of objects over time is associated with the expansion of space itself. However, this

1860-406: Is a maximum distance, called the particle horizon , beyond which nothing can be detected, as the signals could not have reached us yet. Sometimes astrophysicists distinguish between the observable universe and the visible universe. The former includes signals since the end of the inflationary epoch , while the latter includes only signals emitted since recombination . According to calculations,

1984-540: Is accelerating in the present epoch. By assuming a cosmological model, e.g. the Lambda-CDM model , another possibility is to infer the present-day expansion rate from the sizes of the largest fluctuations seen in the cosmic microwave background . A higher expansion rate would imply a smaller characteristic size of CMB fluctuations, and vice versa. The Planck collaboration measured the expansion rate this way and determined H 0 = 67.4 ± 0.5 (km/s)/Mpc . There

2108-469: Is also the density for which the expansion of the universe is poised between continued expansion and collapse. From the Friedmann equations , the value for ρ c {\displaystyle \rho _{\text{c}}} critical density, is: where G is the gravitational constant and H = H 0 is the present value of the Hubble constant . The value for H 0 , as given by

2232-422: Is apparent. The superclusters and filaments seen in smaller surveys are randomized to the extent that the smooth distribution of the universe is visually apparent. It was not until the redshift surveys of the 1990s were completed that this scale could accurately be observed. Another indicator of large-scale structure is the ' Lyman-alpha forest '. This is a collection of absorption lines that appear in

2356-443: Is enough matter and energy to provide for curvature." In part to accommodate such different geometries, the expansion of the universe is inherently general-relativistic. It cannot be modeled with special relativity alone: Though such models exist, they may be at fundamental odds with the observed interaction between matter and spacetime seen in the universe. The images to the right show two views of spacetime diagrams that show

2480-442: Is essentially pressureless, with | p | ≪ ρ c 2 {\displaystyle |p|\ll \rho c^{2}} , while a gas of ultrarelativistic particles (such as a photon gas ) has positive pressure p = ρ c 2 / 3 {\displaystyle p=\rho c^{2}/3} . Negative-pressure fluids, like dark energy, are not experimentally confirmed, but

2604-414: Is exactly equal to the reachable limit (16 billion light-years) added to the current visibility limit (46 billion light-years). Both popular and professional research articles in cosmology often use the term "universe" to mean "observable universe". This can be justified on the grounds that we can never know anything by direct observation about any part of the universe that is causally disconnected from

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2728-424: Is expanding. The words ' space ' and ' universe ', sometimes used interchangeably, have distinct meanings in this context. Here 'space' is a mathematical concept that stands for the three-dimensional manifold into which our respective positions are embedded, while 'universe' refers to everything that exists, including the matter and energy in space, the extra dimensions that may be wrapped up in various strings , and

2852-534: Is known. The object's distance can then be inferred from the observed apparent brightness . Meanwhile, the recession speed is measured through the redshift. Hubble used this approach for his original measurement of the expansion rate, by measuring the brightness of Cepheid variable stars and the redshifts of their host galaxies. More recently, using Type Ia supernovae , the expansion rate was measured to be H 0   =   73.24 ± 1.74 (km/s)/Mpc . This means that for every million parsecs of distance from

2976-443: Is not a generally covariant description but rather only a choice of coordinates . Contrary to common misconception, it is equally valid to adopt a description in which space does not expand and objects simply move apart while under the influence of their mutual gravity. Although cosmic expansion is often framed as a consequence of general relativity , it is also predicted by Newtonian gravity . According to inflation theory ,

3100-475: Is required in describing structures on a cosmic scale because they are often different from how they appear. Gravitational lensing can make an image appear to originate in a different direction from its real source, when foreground objects curve surrounding spacetime (as predicted by general relativity ) and deflect passing light rays. Rather usefully, strong gravitational lensing can sometimes magnify distant galaxies, making them easier to detect. Weak lensing by

3224-400: Is smaller in the past and larger in the future. Extrapolating back in time with certain cosmological models will yield a moment when the scale factor was zero; our current understanding of cosmology sets this time at 13.787 ± 0.020 billion years ago . If the universe continues to expand forever, the scale factor will approach infinity in the future. It is also possible in principle for

3348-584: Is the equation of state parameter . The energy density of such a fluid drops as Nonrelativistic matter has w = 0 {\displaystyle w=0} while radiation has w = 1 / 3 {\displaystyle w=1/3} . For an exotic fluid with negative pressure, like dark energy, the energy density drops more slowly; if w = − 1 {\displaystyle w=-1} it remains constant in time. If w < − 1 {\displaystyle w<-1} , corresponding to phantom energy ,

3472-417: Is the gravitational constant , ρ {\displaystyle \rho } is the energy density within the universe, p {\displaystyle p} is the pressure , c {\displaystyle c} is the speed of light , and Λ {\displaystyle \Lambda } is the cosmological constant. A positive energy density leads to deceleration of

3596-443: Is therefore estimated to be about 46.5 billion light-years. Using the critical density and the diameter of the observable universe, the total mass of ordinary matter in the universe can be calculated to be about 1.5 × 10  kg . In November 2018, astronomers reported that extragalactic background light (EBL) amounted to 4 × 10 photons. As the universe's expansion is accelerating, all currently observable objects, outside

3720-527: Is unknown, and it may be infinite in extent. Some parts of the universe are too far away for the light emitted since the Big Bang to have had enough time to reach Earth or space-based instruments, and therefore lie outside the observable universe. In the future, light from distant galaxies will have had more time to travel, so one might expect that additional regions will become observable. Regions distant from observers (such as us) are expanding away faster than

3844-749: The Hydra-Antlia filament , is a filament that emeges from the Centaurus Cluster , passes under the Zone of Avoidance (ZOA) as the " Puppis filament ", to link up the Lepus Cloud . This filament then passes though a region containing the NGC 1600 Group before crossing the boundary where the gravitional flows of galaxies between the Laniakea and Perseus–Pisces superclusters diverge to link up with

Hydra–Centaurus Supercluster - Misplaced Pages Continue

3968-621: The University of Hawaii 's Institute of Astronomy identified what he called the Pisces–Cetus Supercluster Complex , a structure one billion light-years long and 150 million light-years across in which, he claimed, the Local Supercluster is embedded. The most distant astronomical object identified (as of August of 2024) is a galaxy classified as JADES-GS-z14-0 . In 2009, a gamma ray burst , GRB 090423 ,

4092-440: The equivalence principle of general relativity, the rules of special relativity are locally valid in small regions of spacetime that are approximately flat. In particular, light always travels locally at the speed  c ; in the diagram, this means, according to the convention of constructing spacetime diagrams, that light beams always make an angle of 45° with the local grid lines. It does not follow, however, that light travels

4216-474: The grains of beach sand on planet Earth . Other estimates are in the hundreds of billions rather than trillions. The estimated total number of stars in an inflationary universe (observed and unobserved) is 10 . Assuming the mass of ordinary matter is about 1.45 × 10  kg as discussed above, and assuming all atoms are hydrogen atoms (which are about 74% of all atoms in the Milky Way by mass),

4340-415: The intergalactic medium (IGM). However, it excludes dark matter and dark energy . This quoted value for the mass of ordinary matter in the universe can be estimated based on critical density. The calculations are for the observable universe only as the volume of the whole is unknown and may be infinite. Critical density is the energy density for which the universe is flat. If there is no dark energy, it

4464-418: The large-scale structure of the universe . Around 3 billion years ago, at a time of about 11 billion years, dark energy is believed to have begun to dominate the energy density of the universe. This transition came about because dark energy does not dilute as the universe expands, instead maintaining a constant energy density. Similarly to inflation, dark energy drives accelerated expansion, such that

4588-466: The " proper distance " used in both Hubble's law and in defining the size of the observable universe. Cosmologist Ned Wright argues against using this measure. The proper distance for a redshift of 8.2 would be about 9.2 Gpc , or about 30 billion light-years. The limit of observability in the universe is set by cosmological horizons which limit—based on various physical constraints—the extent to which information can be obtained about various events in

4712-484: The "cosmic web". Prior to 1989, it was commonly assumed that virialized galaxy clusters were the largest structures in existence, and that they were distributed more or less uniformly throughout the universe in every direction. However, since the early 1980s, more and more structures have been discovered. In 1983, Adrian Webster identified the Webster LQG , a large quasar group consisting of 5 quasars. The discovery

4836-660: The 1952 meeting of the International Astronomical Union in Rome. For most of the second half of the 20th century, the value of the Hubble constant was estimated to be between 50 and 90 km⋅s ⋅ Mpc . On 13 January 1994, NASA formally announced a completion of its repairs related to the main mirror of the Hubble Space Telescope , allowing for sharper images and, consequently, more accurate analyses of its observations. Shortly after

4960-439: The Big Bang (4 billion years ago) it began to gradually expand more quickly , and is still doing so. Physicists have postulated the existence of dark energy , appearing as a cosmological constant in the simplest gravitational models, as a way to explain this late-time acceleration. According to the simplest extrapolation of the currently favored cosmological model, the Lambda-CDM model , this acceleration becomes dominant in

5084-557: The Big Bang and that the pre-inflation size of the universe was approximately equal to the speed of light times its age, that would suggest that at present the entire universe's size is at least 1.5 × 10 light-years—at least 3 × 10 times the radius of the observable universe. If the universe is finite but unbounded, it is also possible that the universe is smaller than the observable universe. In this case, what we take to be very distant galaxies may actually be duplicate images of nearby galaxies, formed by light that has circumnavigated

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5208-419: The Big Bang. During the matter-dominated epoch, cosmic expansion also decelerated, with the scale factor growing as the 2/3 power of the time ( a ∝ t 2 / 3 {\displaystyle a\propto t^{2/3}} ). Also, gravitational structure formation is most efficient when nonrelativistic matter dominates, and this epoch is responsible for the formation of galaxies and

5332-754: The Centaurus Supercluster (Hydra–Centaurus) is just a lobe in a greater supercluster, Laniakea , that is centered on the Great Attractor . That supercluster would include the Virgo Supercluster, therefore including the Milky Way where Earth resides. Groups and clusters of galaxies The observable universe is a spherical region of the universe consisting of all matter that can be observed from Earth or its space-based telescopes and exploratory probes at

5456-449: The Earth if the event is less than 16 billion light-years away, but the signal will never reach the Earth if the event is further away. The space before this cosmic event horizon can be called "reachable universe", that is all galaxies closer than that could be reached if we left for them today, at the speed of light; all galaxies beyond that are unreachable. Simple observation will show the future visibility limit (62 billion light-years)

5580-426: The Earth, although many credible theories require a total universe much larger than the observable universe. No evidence exists to suggest that the boundary of the observable universe constitutes a boundary on the universe as a whole, nor do any of the mainstream cosmological models propose that the universe has any physical boundary in the first place. However, some models propose it could be finite but unbounded, like

5704-669: The European Space Agency's Planck Telescope, is H 0 = 67.15 kilometres per second per megaparsec. This gives a critical density of 0.85 × 10  kg/m , or about 5 hydrogen atoms per cubic metre. This density includes four significant types of energy/mass: ordinary matter (4.8%), neutrinos (0.1%), cold dark matter (26.8%), and dark energy (68.3%). Although neutrinos are Standard Model particles, they are listed separately because they are ultra-relativistic and hence behave like radiation rather than like matter. The density of ordinary matter, as measured by Planck,

5828-620: The Giant Void mentioned above. Another large-scale structure is the SSA22 Protocluster , a collection of galaxies and enormous gas bubbles that measures about 200 million light-years across. In 2011, a large quasar group was discovered, U1.11 , measuring about 2.5 billion light-years across. On January 11, 2013, another large quasar group, the Huge-LQG , was discovered, which was measured to be four billion light-years across,

5952-401: The Hubble horizon are not dynamical, because gravitational influences do not have time to propagate across them, while perturbations much smaller than the Hubble horizon are straightforwardly governed by Newtonian gravitational dynamics . An object's peculiar velocity is its velocity with respect to the comoving coordinate grid, i.e., with respect to the average expansion-associated motion of

6076-418: The Hubble rate H {\displaystyle H} quantifies the rate of expansion. H {\displaystyle H} is a function of cosmic time . The expansion of the universe can be understood as a consequence of an initial impulse (possibly due to inflation ), which sent the contents of the universe flying apart. The mutual gravitational attraction of the matter and radiation within

6200-904: The Lepus Cloud are part of a substantial filament known as the Centaurus–Puppis–PP Filament that extends around 420  Mly (130  Mpc ) from the Centaurus Cluster all the way to the Perseus–Pisces supercluster. The Centaurus–Puppis–PP Filament along with the Southern Supercluster Strand which contains the Eridanus-Fornax-Dorado Filament and the Telescopium−Grus Cloud , are part of wall that makes up

6324-489: The NASA/IPAC Extragalactic Database of Galaxy Distances, "Lundmark's extragalactic distance estimates were far more accurate than Hubble's, consistent with an expansion rate (Hubble constant) that was within 1% of the best measurements today." In 1927, Georges Lemaître independently reached a similar conclusion to Friedmann on a theoretical basis, and also presented observational evidence for

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6448-601: The Perseus–Pisces supercluster at a distance of around 420  Mly (130  Mpc ) from the Centaurus Cluster. The filament contains two major clusters: In 2014, it was revealed that the Antlia Wall along with the rest of the Hydra–Centaurus supercluster is connected to the Perseus–Pisces Supercluster. Later in 2017, Pomarède et.al identified based on the flow of galaxies that the Antlia Wall along with

6572-679: The U.K., of light from the brightest part of this web, surrounding and illuminated by a cluster of forming galaxies, acting as cosmic flashlights for intercluster medium hydrogen fluorescence via Lyman-alpha emissions. In 2021, an international team, headed by Roland Bacon from the Centre de Recherche Astrophysique de Lyon (France), reported the first observation of diffuse extended Lyman-alpha emission from redshift 3.1 to 4.5 that traced several cosmic web filaments on scales of 2.5−4  cMpc (comoving mega-parsecs), in filamentary environments outside massive structures typical of web nodes. Some caution

6696-563: The central clusters, which are 150 to 200 million light years away, several smaller clusters belong to the group. Within the proximity of this supercluster lies the Great Attractor , dominated by the Norma Cluster (Abell 3627). This massive cluster of galaxies exerts a large gravitational force, causing all matter within 50 Mpc to experience a bulk flow of 600 km/s toward the Norma Cluster. A 2014 announcement says that

6820-479: The centre of the Hydra–Centaurus Supercluster , a gravitational anomaly called the Great Attractor affects the motion of galaxies over a region hundreds of millions of light-years across. These galaxies are all redshifted , in accordance with Hubble's law . This indicates that they are receding from us and from each other, but the variations in their redshift are sufficient to reveal the existence of

6944-489: The constellation Boötes from observations captured by the Sloan Digital Sky Survey . The End of Greatness is an observational scale discovered at roughly 100  Mpc (roughly 300 million light-years) where the lumpiness seen in the large-scale structure of the universe is homogenized and isotropized in accordance with the cosmological principle . At this scale, no pseudo-random fractalness

7068-457: The cosmic scale factor grew exponentially in time. In order to solve the horizon and flatness problems, inflation must have lasted long enough that the scale factor grew by at least a factor of e (about 10 ). The history of the universe after inflation but before a time of about 1 second is largely unknown. However, the universe is known to have been dominated by ultrarelativistic Standard Model particles, conventionally called radiation , by

7192-513: The cosmic expansion history can also be measured by studying how redshifts, distances, fluxes, angular positions, and angular sizes of astronomical objects change over the course of the time that they are being observed. These effects are too small to have yet been detected. However, changes in redshift or flux could be observed by the Square Kilometre Array or Extremely Large Telescope in the mid-2030s. At cosmological scales,

7316-421: The current comoving distance to particles from which the cosmic microwave background radiation (CMBR) was emitted, which represents the radius of the visible universe, is about 14.0 billion parsecs (about 45.7 billion light-years). The comoving distance to the edge of the observable universe is about 14.3 billion parsecs (about 46.6 billion light-years), about 2% larger. The radius of the observable universe

7440-456: The decay of particles' peculiar momenta, as discussed above. It can also be understood as adiabatic cooling . The temperature of ultrarelativistic fluids, often called "radiation" and including the cosmic microwave background , scales inversely with the scale factor (i.e. T ∝ a − 1 {\displaystyle T\propto a^{-1}} ). The temperature of nonrelativistic matter drops more sharply, scaling as

7564-528: The distance between Earth and the quasar when the light was emitted, and the distance between them in the present era (taking a slice of the cone along the dimension defined as the spatial dimension). The former distance is about 4 billion light-years, much smaller than ct , whereas the latter distance (shown by the orange line) is about 28 billion light-years, much larger than  ct . In other words, if space were not expanding today, it would take 28 billion years for light to travel between Earth and

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7688-509: The distance to that matter at the time the light was emitted, we may first note that according to the Friedmann–Lemaître–Robertson–Walker metric , which is used to model the expanding universe, if we receive light with a redshift of z , then the scale factor at the time the light was originally emitted is given by a ( t ) = 1 1 + z {\displaystyle a(t)={\frac {1}{1+z}}} . WMAP nine-year results combined with other measurements give

7812-545: The edge of the observable universe is about 14.26 giga parsecs (46.5 billion light-years or 4.40 × 10  m) in any direction. The observable universe is thus a sphere with a diameter of about 28.5 gigaparsecs (93 billion light-years or 8.8 × 10  m). Assuming that space is roughly flat (in the sense of being a Euclidean space ), this size corresponds to a comoving volume of about 1.22 × 10  Gpc ( 4.22 × 10  Gly or 3.57 × 10  m ). These are distances now (in cosmological time ), not distances at

7936-635: The edge of the observable universe is the age of the universe times the speed of light , 13.8 billion light years. This is the distance that a photon emitted shortly after the Big Bang, such as one from the cosmic microwave background , has traveled to reach observers on Earth. Because spacetime is curved, corresponding to the expansion of space , this distance does not correspond to the true distance at any moment in time. The observable universe contains as many as an estimated 2 trillion galaxies and, overall, as many as an estimated 10 stars – more stars (and, potentially, Earth-like planets) than all

8060-416: The energy density grows as the universe expands. Inflation is a period of accelerated expansion hypothesized to have occurred at a time of around 10 seconds. It would have been driven by the inflaton , a field that has a positive-energy false vacuum state. Inflation was originally proposed to explain the absence of exotic relics predicted by grand unified theories , such as magnetic monopoles , because

8184-415: The environment of the cluster looks somewhat pinched if using redshifts to measure distance. The opposite effect is observed on galaxies already within a cluster: the galaxies have some random motion around the cluster center, and when these random motions are converted to redshifts, the cluster appears elongated. This creates a " finger of God "—the illusion of a long chain of galaxies pointed at Earth. At

8308-467: The estimated total number of atoms in the observable universe is obtained by dividing the mass of ordinary matter by the mass of a hydrogen atom. The result is approximately 10 hydrogen atoms, also known as the Eddington number . The mass of the observable universe is often quoted as 10  kg. In this context, mass refers to ordinary (baryonic) matter and includes the interstellar medium (ISM) and

8432-405: The evidence that leads to the inflationary model of the early universe also implies that the "total universe" is much larger than the observable universe. Thus any edges or exotic geometries or topologies would not be directly observable, since light has not reached scales on which such aspects of the universe, if they exist, are still allowed. For all intents and purposes, it is safe to assume that

8556-506: The existence of dark energy is inferred from astronomical observations. In an expanding universe, it is often useful to study the evolution of structure with the expansion of the universe factored out. This motivates the use of comoving coordinates , which are defined to grow proportionally with the scale factor. If an object is moving only with the Hubble flow of the expanding universe, with no other motion, then it remains stationary in comoving coordinates. The comoving coordinates are

8680-469: The expansion, a ¨ < 0 {\displaystyle {\ddot {a}}<0} , and a positive pressure further decelerates expansion. On the other hand, sufficiently negative pressure with p < − ρ c 2 / 3 {\displaystyle p<-\rho c^{2}/3} leads to accelerated expansion, and the cosmological constant also accelerates expansion. Nonrelativistic matter

8804-401: The first few billion years of its travel time, also indicating that the expansion of space between Earth and the quasar at the early time was faster than the speed of light. None of this behavior originates from a special property of metric expansion, but rather from local principles of special relativity integrated over a curved surface. Over time, the space that makes up the universe

8928-510: The first year observations of the Wilkinson Microwave Anisotropy Probe satellite (WMAP) further agreed with the estimated expansion rates for local galaxies, 72 ± 5 km⋅s ⋅Mpc . The universe at the largest scales is observed to be homogeneous (the same everywhere) and isotropic (the same in all directions), consistent with the cosmological principle . These constraints demand that any expansion of

9052-622: The front boundary of the Sculptor Void . Before 2017, it was not known that the Antlia Wall and the Lepus Cloud were part of the same structure, the Centaurus–Puppis–PP Filament. This is because the Centaurus–Puppis–PP Filament goes under the ZOA of the Milky Way , which caused parts of the filament to be obscured by the disk of the galaxy on the sky, resulting in the naming of the different visible pieces of filament. Apart from

9176-425: The future because light emitted by objects outside that limit could never reach the Earth. Note that, because the Hubble parameter is decreasing with time, there can be cases where a galaxy that is receding from Earth only slightly faster than light emits a signal that eventually reaches Earth. This future visibility limit is calculated at a comoving distance of 19 billion parsecs (62 billion light-years), assuming

9300-420: The future" over long distances. However, within general relativity , the shape of these comoving synchronous spatial surfaces is affected by gravity. Current observations are consistent with these spatial surfaces being geometrically flat (so that, for example, the angles of a triangle add up to 180 degrees). An expanding universe typically has a finite age. Light, and other particles, can have propagated only

9424-502: The future. In 1912–1914, Vesto Slipher discovered that light from remote galaxies was redshifted , a phenomenon later interpreted as galaxies receding from the Earth. In 1922, Alexander Friedmann used the Einstein field equations to provide theoretical evidence that the universe is expanding. Swedish astronomer Knut Lundmark was the first person to find observational evidence for expansion, in 1924. According to Ian Steer of

9548-429: The galaxy looked like 10 billion years after the Big Bang, even though it remains at the same comoving distance less than that of the observable universe. This can be used to define a type of cosmic event horizon whose distance from the Earth changes over time. For example, the current distance to this horizon is about 16 billion light-years, meaning that a signal from an event happening at present can eventually reach

9672-418: The infinite extent of the expanse. All that is certain is that the manifold of space in which we live simply has the property that the distances between objects are getting larger as time goes on. This only implies the simple observational consequences associated with the metric expansion explored below. No "outside" or embedding in hyperspace is required for an expansion to occur. The visualizations often seen of

9796-432: The infinite future. This implies that the amount of the universe that we will ever be able to observe is limited. Many systems exist whose light can never reach us, because there is a cosmic event horizon induced by the repulsive gravity of the dark energy. Within the study of the evolution of structure within the universe, a natural scale emerges, known as the Hubble horizon . Cosmological perturbations much larger than

9920-433: The intervening universe in general also subtly changes the observed large-scale structure. The large-scale structure of the universe also looks different if only redshift is used to measure distances to galaxies. For example, galaxies behind a galaxy cluster are attracted to it and fall towards it, and so are blueshifted (compared to how they would be if there were no cluster). On the near side, objects are redshifted. Thus,

10044-413: The inverse square of the scale factor (i.e. T ∝ a − 2 {\displaystyle T\propto a^{-2}} ). The contents of the universe dilute as it expands. The number of particles within a comoving volume remains fixed (on average), while the volume expands. For nonrelativistic matter, this implies that the energy density drops as ρ ∝

10168-409: The large-scale geometry of the universe according to the ΛCDM cosmological model. Two of the dimensions of space are omitted, leaving one dimension of space (the dimension that grows as the cone gets larger) and one of time (the dimension that proceeds "up" the cone's surface). The narrow circular end of the diagram corresponds to a cosmological time of 700 million years after the Big Bang, while

10292-689: The largest known structure in the universe at that time. In November 2013, astronomers discovered the Hercules–Corona Borealis Great Wall , an even bigger structure twice as large as the former. It was defined by the mapping of gamma-ray bursts . In 2021, the American Astronomical Society announced the detection of the Giant Arc ; a crescent-shaped string of galaxies that span 3.3 billion light years in length, located 9.2 billion light years from Earth in

10416-436: The local supercluster , will eventually appear to freeze in time, while emitting progressively redder and fainter light. For instance, objects with the current redshift z from 5 to 10 will only be observable up to an age of 4–6 billion years. In addition, light emitted by objects currently situated beyond a certain comoving distance (currently about 19 gigaparsecs (62 Gly)) will never reach Earth. The universe's size

10540-550: The observer, recessional velocity of objects at that distance increases by about 73 kilometres per second (160,000 mph). Supernovae are observable at such great distances that the light travel time therefrom can approach the age of the universe. Consequently, they can be used to measure not only the present-day expansion rate but also the expansion history. In work that was awarded the 2011 Nobel Prize in Physics , supernova observations were used to determine that cosmic expansion

10664-423: The particle count, the energy of each particle (including the rest mass energy ) also drops significantly due to the decay of peculiar momenta. In general, we can consider a perfect fluid with pressure p = w ρ {\displaystyle p=w\rho } , where ρ {\displaystyle \rho } is the energy density. The parameter w {\displaystyle w}

10788-534: The position of galaxies in three dimensions, which involves combining location information about the galaxies with distance information from redshifts . Two years later, astronomers Roger G. Clowes and Luis E. Campusano discovered the Clowes–Campusano LQG , a large quasar group measuring two billion light-years at its widest point, which was the largest known structure in the universe at the time of its announcement. In April 2003, another large-scale structure

10912-435: The present era (less in the past and more in the future). The circular curling of the surface is an artifact of the embedding with no physical significance and is done for illustrative purposes; a flat universe does not curl back onto itself. (A similar effect can be seen in the tubular shape of the pseudosphere .) The brown line on the diagram is the worldline of Earth (or more precisely its location in space, even before it

11036-468: The present time; the electromagnetic radiation from these objects has had time to reach the Solar System and Earth since the beginning of the cosmological expansion . Assuming the universe is isotropic , the distance to the edge of the observable universe is roughly the same in every direction. That is, the observable universe is a spherical region centered on the observer. Every location in

11160-416: The present universe conforms to Euclidean space , what cosmologists describe as geometrically flat , to within experimental error. Consequently, the rules of Euclidean geometry associated with Euclid's fifth postulate hold in the present universe in 3D space. It is, however, possible that the geometry of past 3D space could have been highly curved. The curvature of space is often modeled using

11284-418: The quasar, while if the expansion had stopped at the earlier time, it would have taken only 4 billion years. The light took much longer than 4 billion years to reach us though it was emitted from only 4 billion light-years away. In fact, the light emitted towards Earth was actually moving away from Earth when it was first emitted; the metric distance to Earth increased with cosmological time for

11408-416: The rapid expansion would have diluted such relics. It was subsequently realized that the accelerated expansion would also solve the horizon problem and the flatness problem . Additionally, quantum fluctuations during inflation would have created initial variations in the density of the universe, which gravity later amplified to yield the observed spectrum of matter density variations . During inflation,

11532-421: The redshift of photon decoupling as z  =  1 091 .64 ± 0.47 , which implies that the scale factor at the time of photon decoupling would be 1 ⁄ 1092.64 . So if the matter that originally emitted the oldest CMBR photons has a present distance of 46 billion light-years, then the distance would have been only about 42 million light-years at the time of decoupling. The light-travel distance to

11656-465: The repairs were made, Wendy Freedman 's 1994 Key Project analyzed the recession velocity of M100 from the core of the Virgo Cluster , offering a Hubble constant measurement of 80 ± 17 km⋅s ⋅Mpc . Later the same year, Adam Riess et al. used an empirical method of visual-band light-curve shapes to more finely estimate the luminosity of Type Ia supernovae . This further minimized

11780-567: The same place like going all the way around the surface of a balloon (or a planet like the Earth), is an observational question that is constrained as measurable or non-measurable by the universe's global geometry . At present, observations are consistent with the universe having infinite extent and being a simply connected space , though cosmological horizons limit our ability to distinguish between simple and more complicated proposals. The universe could be infinite in extent or it could be finite; but

11904-527: The same velocity as its own. More generally, the peculiar momenta of both relativistic and nonrelativistic particles decay in inverse proportion with the scale factor. For photons, this leads to the cosmological redshift . While the cosmological redshift is often explained as the stretching of photon wavelengths due to "expansion of space", it is more naturally viewed as a consequence of the Doppler effect . The universe cools as it expands. This follows from

12028-424: The scale factor grows exponentially in time. The most direct way to measure the expansion rate is to independently measure the recession velocities and the distances of distant objects, such as galaxies. The ratio between these quantities gives the Hubble rate, in accordance with Hubble's law. Typically, the distance is measured using a standard candle , which is an object or event for which the intrinsic brightness

12152-620: The spatial coordinates in the FLRW metric . The universe is a four-dimensional spacetime, but within a universe that obeys the cosmological principle, there is a natural choice of three-dimensional spatial surface. These are the surfaces on which observers who are stationary in comoving coordinates agree on the age of the universe . In a universe governed by special relativity , such surfaces would be hyperboloids , because relativistic time dilation means that rapidly receding distant observers' clocks are slowed, so that spatial surfaces must bend "into

12276-563: The spectra of light from quasars , which are interpreted as indicating the existence of huge thin sheets of intergalactic (mostly hydrogen ) gas. These sheets appear to collapse into filaments, which can feed galaxies as they grow where filaments either cross or are dense. An early direct evidence for this cosmic web of gas was the 2019 detection, by astronomers from the RIKEN Cluster for Pioneering Research in Japan and Durham University in

12400-414: The speed of light, at rates estimated by Hubble's law . The expansion rate appears to be accelerating , which dark energy was proposed to explain. Assuming dark energy remains constant (an unchanging cosmological constant ) so that the expansion rate of the universe continues to accelerate, there is a "future visibility limit" beyond which objects will never enter the observable universe at any time in

12524-404: The surface of last scattering for neutrinos and gravitational waves . Metric expansion of space The expansion of the universe is the increase in distance between gravitationally unbound parts of the observable universe with time. It is an intrinsic expansion, so it does not mean that the universe expands "into" anything or that space exists "outside" it. To any observer in

12648-474: The surrounding material. It is a measure of how a particle's motion deviates from the Hubble flow of the expanding universe. The peculiar velocities of nonrelativistic particles decay as the universe expands, in inverse proportion with the cosmic scale factor . This can be understood as a self-sorting effect. A particle that is moving in some direction gradually overtakes the Hubble flow of cosmic expansion in that direction, asymptotically approaching material with

12772-426: The systematic measurement errors of the Hubble constant, to 67 ± 7 km⋅s ⋅Mpc . Reiss's measurements on the recession velocity of the nearby Virgo Cluster more closely agree with subsequent and independent analyses of Cepheid variable calibrations of Type Ia supernova , which estimates a Hubble constant of 73 ± 7 km⋅s ⋅Mpc . In 2003, David Spergel 's analysis of the cosmic microwave background during

12896-413: The time of neutrino decoupling at about 1 second. During radiation domination, cosmic expansion decelerated, with the scale factor growing proportionally with the square root of the time. Since radiation redshifts as the universe expands, eventually nonrelativistic matter came to dominate the energy density of the universe. This transition happened at a time of about 50 thousand years after

13020-476: The time the light was emitted. For example, the cosmic microwave background radiation that we see right now was emitted at the time of photon decoupling , estimated to have occurred about 380,000 years after the Big Bang, which occurred around 13.8 billion years ago. This radiation was emitted by matter that has, in the intervening time, mostly condensed into galaxies, and those galaxies are now calculated to be about 46 billion light-years from Earth. To estimate

13144-413: The time through which various events take place. The expansion of space is in reference to this 3D manifold only; that is, the description involves no structures such as extra dimensions or an exterior universe. The ultimate topology of space is a posteriori – something that in principle must be observed – as there are no constraints that can simply be reasoned out (in other words there cannot be any

13268-414: The universe accord with Hubble's law , in which objects recede from each observer with velocities proportional to their positions with respect to that observer. That is, recession velocities v → {\displaystyle {\vec {v}}} scale with (observer-centered) positions x → {\displaystyle {\vec {x}}} according to where

13392-415: The universe gradually slows this expansion over time, but expansion nevertheless continues due to momentum left over from the initial impulse. Also, certain exotic relativistic fluids , such as dark energy and inflation, exert gravitational repulsion in the cosmological context, which accelerates the expansion of the universe. A cosmological constant also has this effect. Mathematically, the expansion of

13516-422: The universe has its own observable universe, which may or may not overlap with the one centered on Earth. The word observable in this sense does not refer to the capability of modern technology to detect light or other information from an object, or whether there is anything to be detected. It refers to the physical limit created by the speed of light itself. No signal can travel faster than light, hence there

13640-462: The universe is infinite in spatial extent, without edge or strange connectedness. Regardless of the overall shape of the universe, the question of what the universe is expanding into is one that does not require an answer, according to the theories that describe the expansion; the way we define space in our universe in no way requires additional exterior space into which it can expand, since an expansion of an infinite expanse can happen without changing

13764-402: The universe is quantified by the scale factor , a {\displaystyle a} , which is proportional to the average separation between objects, such as galaxies. The scale factor is a function of time and is conventionally set to be a = 1 {\displaystyle a=1} at the present time. Because the universe is expanding, a {\displaystyle a}

13888-646: The universe suddenly expanded during the inflationary epoch (about 10 of a second after the Big Bang), and its volume increased by a factor of at least 10 (an expansion of distance by a factor of at least 10 in each of the three dimensions). This would be equivalent to expanding an object 1  nanometer across ( 10  m , about half the width of a molecule of DNA ) to one approximately 10.6  light-years across (about 10  m , or 62 trillion miles). Cosmic expansion subsequently decelerated to much slower rates, until around 9.8 billion years after

14012-424: The universe to stop expanding and begin to contract, which corresponds to the scale factor decreasing in time. The scale factor a {\displaystyle a} is a parameter of the FLRW metric , and its time evolution is governed by the Friedmann equations . The second Friedmann equation, shows how the contents of the universe influence its expansion rate. Here, G {\displaystyle G}

14136-509: The universe will keep expanding forever, which implies the number of galaxies that can ever be theoretically observed in the infinite future is only larger than the number currently observable by a factor of 2.36 (ignoring redshift effects). In principle, more galaxies will become observable in the future; in practice, an increasing number of galaxies will become extremely redshifted due to ongoing expansion, so much so that they will seem to disappear from view and become invisible. A galaxy at

14260-408: The universe, it appears that all but the nearest galaxies (which are bound to each other by gravity) move away at speeds that are proportional to their distance from the observer , on average. While objects cannot move faster than light , this limitation applies only with respect to local reference frames and does not limit the recession rates of cosmologically distant objects. Cosmic expansion

14384-537: The universe. It is difficult to test this hypothesis experimentally because different images of a galaxy would show different eras in its history, and consequently might appear quite different. Bielewicz et al. claim to establish a lower bound of 27.9 gigaparsecs (91 billion light-years) on the diameter of the last scattering surface. This value is based on matching-circle analysis of the WMAP 7-year data. This approach has been disputed. The comoving distance from Earth to

14508-403: The universe. The most famous horizon is the particle horizon which sets a limit on the precise distance that can be seen due to the finite age of the universe . Additional horizons are associated with the possible future extent of observations, larger than the particle horizon owing to the expansion of space , an "optical horizon" at the surface of last scattering , and associated horizons with

14632-431: The various wavelength bands of electromagnetic radiation (in particular 21-cm emission ) have yielded much information on the content and character of the universe 's structure. The organization of structure appears to follow a hierarchical model with organization up to the scale of superclusters and filaments . Larger than this (at scales between 30 and 200 megaparsecs), there seems to be no continued structure,

14756-412: The wide end is a cosmological time of 18 billion years, where one can see the beginning of the accelerating expansion as a splaying outward of the spacetime, a feature that eventually dominates in this model. The purple grid lines mark cosmological time at intervals of one billion years from the Big Bang. The cyan grid lines mark comoving distance at intervals of one billion light-years in

14880-469: Was discovered, the Giant Void , which measures 1.3 billion light-years across. Based on redshift survey data, in 1989 Margaret Geller and John Huchra discovered the " Great Wall ", a sheet of galaxies more than 500 million light-years long and 200 million light-years wide, but only 15 million light-years thick. The existence of this structure escaped notice for so long because it requires locating

15004-486: Was discovered, the Sloan Great Wall . In August 2007, a possible supervoid was detected in the constellation Eridanus . It coincides with the ' CMB cold spot ', a cold region in the microwave sky that is highly improbable under the currently favored cosmological model. This supervoid could cause the cold spot, but to do so it would have to be improbably big, possibly a billion light-years across, almost as big as

15128-443: Was formed). The yellow line is the worldline of the most distant known quasar . The red line is the path of a light beam emitted by the quasar about 13 billion years ago and reaching Earth at the present day. The orange line shows the present-day distance between the quasar and Earth, about 28 billion light-years, which is a larger distance than the age of the universe multiplied by the speed of light,  ct . According to

15252-450: Was found to have a redshift of 8.2, which indicates that the collapsing star that caused it exploded when the universe was only 630 million years old. The burst happened approximately 13 billion years ago, so a distance of about 13 billion light-years was widely quoted in the media, or sometimes a more precise figure of 13.035 billion light-years. This would be the "light travel distance" (see Distance measures (cosmology) ) rather than

15376-417: Was the first identification of a large-scale structure, and has expanded the information about the known grouping of matter in the universe. In 1987, Robert Brent Tully identified the Pisces–Cetus Supercluster Complex , the galaxy filament in which the Milky Way resides. It is about 1 billion light-years across. That same year, an unusually large region with a much lower than average distribution of galaxies

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