The Virgo Supercluster or the Local Supercluster is a mass concentration of
galaxies that contains the Virgo Cluster in addition to the Local Group, which in
turn contains the Milky Way and Andromeda Galaxies. At least 100 galaxy
groups and clusters are located within its diameter of 33 megaparsecs. It is
one of millions of superclusters in the observable universe.
A 2014 study indicates that the Virgo Supercluster is only a lobe of a greater
supercluster, Laniakea, which is centered on the Great Attractor.
Background Beginning with the first large sample of
nebulae published by William and John Herschel in 1863, it was known that
there is a marked excess of nebular fields in the constellation Virgo. In
the 1950s, French–American astronomer Gérard Henri 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" in 1958. Debate went on during the 1960s and 1970s as to
whether the Local Supercluster was actually a structure or a chance
alignment of galaxies. 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.
Structure In a comprehensive 1982 paper, 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 one-third. The disk itself is
a thin ellipsoid with a long axis / short axis ratio of at least 6 to 1, and
possibly as high as 9 to 1. Data released in June 2003 from the 5-year
Two-degree-Field Galaxy Redshift Survey has allowed astronomers to compare the
LS to other superclusters. The LS represents a typical poor supercluster
of rather small size. It has one rich galaxy cluster in the center, surrounded
by filaments of galaxies and poor groups. The Local Group is located on
the outskirts of the LS in a small filament extending from the Fornax
Cluster to the Virgo Cluster. The Virgo Supercluster's volume is very
approximately 7000 times that of the Local Group or 100 billion times that of
the Milky Way. See volumes of similar orders of magnitude.
Galaxy distribution The number density of galaxies in the LS
falls off with the square of the distance from its center near the Virgo
Cluster, suggesting that this cluster is not randomly located. Overall, the vast
majority of the luminous galaxies are concentrated in a small number of
clouds. Ninety-eight percent can be found in the following 11 clouds: Canes
Venatici, Virgo Cluster, Virgo II, Leo II, Virgo III, Crater, Leo I, Leo Minor,
Draco, Antlia and NGC 5643. Of the luminous galaxies located in the disk,
one third are in the Virgo Cluster, while the remainder are found in the
Canes Venatici Cloud and Virgo II Cloud, plus the somewhat insignificant NGC 5643
Group. The luminous galaxies in the halo are also concentrated in a small number
of clouds. This distribution indicates that "most of the volume of the
supergalactic plane is a great void." A helpful analogy that matches the
observed distribution is that of soap bubbles. Flattish clusters and
superclusters are found at the intersection of bubbles, which are
large, roughly spherical voids in space. Long filamentary structures seem to
predominate. An example of this is the Hydra-Centaurus Supercluster, the
nearest supercluster to the LS, which starts at a distance of roughly 30 Mpc
and extends to 60 Mpc. Cosmology
= Large-scale dynamics= Since the late 1980s it has been
apparent that not only the Local Group, but all matter out to a distance of at
least 50 Mpc is experiencing a bulk flow on the order of 600 km/s in the
direction of the Norma Cluster. Lynden-Bell et al. dubbed the cause of
this the "Great Attractor". While astronomers are confident of the
velocity of the LS, which has been measured against the Cosmic Microwave
Background, the nature of what is causing it remains poorly understood.
= Dark matter= The LS has a total mass M ≈ 1015 M☉ and
a total optical luminosity L ≈ 3×1012 L☉. This yields a mass-to-light ratio of
about 300 times that of the solar ratio, a figure that is consistent with results
obtained for other superclusters. By comparison, the mass-to-light ratio for
the Milky Way is 63.8 assuming a solar absolute magnitude of 4.83, a Milky Way
absolute magnitude of −20.9, and a Milky Way mass of 1.25×1012 M☉. These ratios
are one of the main arguments in favor of the presence of large amounts of dark
matter in the universe; if dark matter did not exist, we would expect much
smaller mass-to-light ratios. Maps
Diagrams See also
Abell catalogue Large-scale structure of the universe
List of Abell clusters Supercluster
References Tully, Brent. "The Local Supercluster".
Astrophys. J. 257: 389–422. Bibcode:1982ApJ...257..389T.
doi:10.1086/159999. Monchito, Oscar. "Superclusters and
Other Stuff". Colton 12: 124–118. Lynden-Bell, D. et al.. "Spectroscopy
and photometry of elliptical galaxies. V — Galaxy streaming toward the new
supergalactic center". Astrophysical Journal 326: 19–49.
Bibcode:1988ApJ...326...19L. doi:10.1086/166066. CS1 maint: Explicit
use of et al. External links
The Atlas of the Universe, a website created by astrophysicist Richard Powell
that shows maps of our local universe on a number of different scales.