| Local Supercluster | |
|---|---|
 Distances from theLocal Group for selected groups and clusters within the Local Supercluster[citation needed] | |
| Observation data (EpochJ2000) | |
| Constellation(s) | Virgo &Coma Berenices (Virgo Cluster) |
| Right ascension | 12h 31m[1] |
| Declination | +12° 24′[1] |
| Number of galaxies | 47,000+ |
| Parent structure | Laniakea Supercluster |
| Major axis | 147 Mly (45 Mpc)[2] |
| Minor axis | ≈26.1 Mly (8 Mpc)[3] |
| Redshift | Doppler shift[citation needed] |
| Distance | 55.62 ± 8.395 Mly (17.053 ± 2.574 Mpc) (Virgo Cluster)[4] |
| Binding mass | ~1.48×1015[5] M☉ |
| Luminosity (specify) | 3×1012 L☉[5] (total) |
| Other designations | |
| Local Supercluster, Virgo Supercluster, LSC, LS[1] | |
TheLocal Supercluster (LSC orLS) is asupercluster ofgalaxies containing theVirgo Cluster andLocal Group. The latter contains theMilky Way andAndromeda galaxies, among others. Sometimes referred to asVirgo Supercluster, the Local Supercluster is roughly centered on the Virgo Cluster, with the Local Group located near one edge and revolving around its center.[6]
At least 100galaxy groups andclusters[7] are located within the supercluster diameter of 45megaparsecs (147 millionlight-years; 1.39×1021kilometres).[2] The Local Supercluster is one of about 10 million superclusters in theobservable universe, with the main body of the supercluster, the Virgo Strand, connecting theHydra-Centaurus and thePerseus–Pisces Superclusters.[8] It is part of thePisces–Cetus Supercluster Complex, avery largegalaxy filament.[9][10]
A 2014 study indicated that the Local Supercluster is only a part of an even greater supercluster centered on theGreat Attractor,Laniakea Supercluster.[11] This thus would subsume the former as a component under Laniakea as the newly defined local supercluster based on the definition for a supercluster as basins of attraction rather than large high-density regions as traditionally accepted. Basins of attraction such as Laniakea were later proposed to be calledsupercluster cocoons to distinguish them from smaller and traditional superclusters, such as Virgo, as high-density regions of thecosmic web.[12]
Beginning with the first large sample ofnebulae published byWilliam andJohn Herschel in 1863, it was known that there is a marked excess of nebular fields in the constellationVirgo, near the northgalactic pole. In the 1950s, French–American astronomerGérard de Vaucouleurs was the first to argue that this excess represented a large-scale galaxy-like structure, coining the term "Local Supergalaxy" in 1953, which he changed to "Local Supercluster" (LSC[13]) in 1958.Harlow Shapley, in his 1959 bookOf Stars and Men, suggested the termMetagalaxy.[14]
Debate went on during the 1960s and 1970s as to whether the Local Supercluster (LS) was actually a structure or a chance alignment of galaxies.[15] The issue was resolved with the large redshift surveys of the late 1970s and early 1980s, which convincingly showed the flattened concentration of galaxies along the supergalactic plane.[2]
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In 1982,R. Brent Tully presented the conclusions of his research concerning the basic structure of the LS. It consists of two components: an appreciably flattened disk containing two-thirds of the supercluster's luminous galaxies, and a roughly spherical halo containing the remaining third.[16] The disk itself is a thin (~1 Mpc) ellipsoid with a long axis / short axis ratio of at least 6 to 1, and possibly as high as 9 to 1.[17] Data released in June 2003 from the 5-yearTwo-degree-Field Galaxy Redshift Survey (2dF) has allowed astronomers to compare the LS to other superclusters. The LS represents a typical poor (that is, lacking a high density core) supercluster of rather small size. It has one rich galaxy cluster in the center, surrounded by filaments of galaxies and poor groups.[5]
TheLocal Group is located on the outskirts of the LS in a small filament extending from theFornax Cluster to theVirgo Cluster.[2] The Virgo Supercluster's volume is roughly 7,000 times that of the Local Group, or 100 billion times that of the Milky Way.
The main body of the Virgo Supercluster, the flattened disk of galaxies is simply part of a largergalaxy filament known as theVirgo Strand orCentaurus–Virgo–PP Filament.[18][8] This filament emanates from theCentaurus Cluster through theVirgo Cluster and continues through theUrsa Major Cluster all the way to thePerseus–Pisces Supercluster.[8] TheVirgo Strand consists of two branches, an upper branch consisting of the main body of the supercluster though theVirgo Southern Extension, theVirgo and theUrsa Major Cluster, and a lower branch consisting of theCrater andLeo Clouds.[18] The rest of remaining third of the galaxies in Virgo Supercluster, including the Milky Way, lie outside the main body of the Supercluster which is theVirgo Strand.[17][18]
Thenumber density of galaxies in the LS falls off with the square of the distance from its center near theVirgo Cluster, suggesting that this cluster is not randomly located. Overall, the vast majority of the luminous galaxies (less thanabsolute magnitude −13) are concentrated in a small number ofclouds (groups ofgalaxy clusters). Ninety-eight percent can be found in the following 11 clouds, given in decreasing order of number of luminous galaxies:Canes Venatici, Virgo Cluster,Virgo II (southern extension),Leo II,Virgo III, Crater (NGC 3672),Leo I, Leo Minor (NGC 2841), Draco (NGC 5907), Antlia (NGC 2997), andNGC 5643.[17]
Of the luminous galaxies located in the disk, one-third are in the Virgo Cluster, with the other two-thirds located outside of the cluster.[17]
The luminous galaxies in the halo are concentrated in a small number of clouds (94% in 7 clouds). This distribution indicates that "most of the volume of the supergalactic plane is a great void."[17] A helpful analogy that matches the observed distribution is that of soap bubbles. Flattish clusters andsuperclusters are found at the intersection of bubbles, which are large, roughly spherical (on the order of 20–60Mpc in diameter) voids in space.[19] Long filamentary structures seem to predominate. An example of this is theHydra–Centaurus Supercluster, the nearest supercluster to the Virgo Supercluster, which starts at a distance of roughly 30 Mpc and extends to 60 Mpc.[20]
Below is a table of known supercluster members.
| Cluster name | Brightest member |
|---|---|
| Local Group | - |
| Virgo Cluster | Messier 49 |
| Sculptor Group | NGC 253 |
| IC 342/Maffei Group | IC 342/Dwingeloo 1 |
| M 81 Group | M 81 |
| Canes I Group | M 94 |
| Canes II Group | M 106 |
| NGC 5128 Group | Centaurus A[21] |
| Leo I Group | M 96 |
| Leo II Groups | - |
Since the late 1980s it has been apparent that not only theLocal Group, but all matter out to a distance of at least 50Mpc is experiencing a bulk flow on the order of 600 km/s in the direction of theNorma Cluster (Abell 3627).[22]Lynden-Bell et al. (1988) dubbed the cause of this the "Great Attractor". The Great Attractor is now understood to be the center of mass of an even larger structure of galaxy clusters and basin of attraction (BoA), dubbed "Laniakea", which includes the Virgo Supercluster (including the Local Group) as well as the Hydra-Centaurus, Pavo-Indus, and Southern Superclusters. Laniakea has therefore been proposed to be called asupercluster cocoon instead to distinguish the structure from smaller embedded superclusters traditionally defined as high-density regions.[12]
The Great Attractor, together with the entire Laniakea, is found to be moving towardShapley Supercluster, with center ofShapley Attractor,[23] and may be itself potentially part of this even greater concentration.[24][25]
The LS has a total massM ≈1015 M☉ and a total optical luminosityL ≈3×1012 L☉.[5] This yields amass-to-light ratio of about 300 times that of the solar ratio (M☉/L☉ = 1), a figure that is consistent with results obtained for other superclusters.[26][27]By comparison, themass-to-light ratio for theMilky Way is 63.8 assuming a solarabsolute magnitude of 4.83,[28] a Milky Way absolute magnitude of −20.9,[29]and a Milky Way mass of1.25×1012 M☉.[30] These ratios are one of the main arguments in favor of the presence of large amounts ofdark matter in the universe; if dark matter did not exist, much smaller mass-to-light ratios would be expected.
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{{cite web}}:Missing or empty|title= (help)| Local Sheet | | |
|---|---|---|
| Others | ||
| Included | Earth →Solar System →Local Interstellar Cloud →Local Bubble →Gould Belt →Orion Arm →Milky Way →Milky Way subgroup →Local Group→Local Sheet→Local Volume→Virgo Supercluster→Laniakea Supercluster →Pisces–Cetus Supercluster Complex →Local Hole →Observable universe →Universe Each arrow (→) may be read as "within" or "part of". |
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| Related | |
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