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the great attractor

• mia kumagai
• astr007.301
• 4.21.06

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what is the great attractor?

• a gravitational anomaly in intergalactic space at
  the center of the local supercluster which
  reveals the existence of a localized
  concentration of mass equivalent to tens of
  thousands of galaxies
• observable by its effect on the motion of
  galaxies over a region hundreds of millions of
  lightyears across
• these galaxies are all redshifted, in accordance
  with the Hubble Flow, indicating that they are
  receding relative to us and to each other, but
  the variations in their redshift are sufficient
  to reveal the existence of the anomaly

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where is the Great Attractor?

• discovered in 1986, it is located in the
  direction of the Hydra and Centaurus
  constellations
• a group of astronomers known as the "Seven
  Samurai" (David Burstein, Roger Davies, Alan
  Dressler, Sandra Faber, Donald Lynden-Bell,
  Roberto J. Terlevich, and Gary Wegner) found
  that galaxies are very unevenly distributed in
  space, with galactic superclusters separated by
  incredibly huge voids of visible ordinary matter

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what is the Great Attractor?

• the Great Attractor is one such structure, a
  diffuse concentration of matter some 400 million
  light-years in size located around 250 million
  light-years away in the direction of the southern
  Constellation Centaurus, about seven degrees off
  the plane of the Milky Way -- at a
  redshift-distance of 4,350 kilometers (or around
  2,700 miles) per second
• a diffuse mass concentration 250 million
  light-years away but so large it pulls our own
  Milky Way Galaxy along with millions of others
  towards it

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observing the Great Attractor

• calculations indicate that 1016 solar masses
  concentrated 65 Mpc away in the direction of
  Centaurus would account for this
• detailed investigation of that region of the sky
  10 times too little visible matter to account for
  this flow, again implying a dominant
  gravitational role for unseen or dark matter
• thus the Great Attractor is certainly there
  (because we see its gravitational influence), but
  the major portion of the mass that must be there
  cannot be seen in our telescopes
• attempts to further study the Great Attractor and
  other phenomena are hampered due to the line of
  sight obstruction by its location in the zone of
  avoidance (the part of the night sky obscured by
  the Milky Way galaxy)

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the Great Attractor in fiction

• the Great Attractor is an element of Stephen
  Baxter's Xeelee Sequence of novels
• In the motion picture Men In Black, J (Will
  Smith) accidentally sends a small, shiny object
  flying and bouncing around MIB headquarters,
  causing a commotion. K (Tommy Lee Jones) explains
  to him that it was a gift from the Great
  Attractor, who thought it was "funny as hell.
• In Terry Pratchetts Discworld series, Azrael,
  the cosmic representation of the Death of
  Universes, is known as the Great Attractor.

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summary

• the Great Attractor is far bigger than a galaxy
• the Great Attractor is a supercluster, or
  something even bigger
• the gravity of the Great Attractor has been
  pulling the Milky Way in its direction - the
  motion of local galaxies indicated there was
  something massive out there that are pulling the
  Milky Way, the Andromeda Galaxy, and other nearby
  galaxies towards it
• for a while, nobody could see what it was,
  because it lies behind the plane of our galaxy,
  meaning the gas and dust in our Galaxy obscures
  the light from the Great Attractor, and it is
  outshone by the stars and other objects in our
  Galaxy
• x-ray observations with the ROSAT satellite then
  revealed that Abell 3627, a previously known
  cluster of galaxies, was much more massive than
  originally suspected, containing many more
  galaxies
• optical astronomers had missed a great number of
  galaxies, because of the obscuration, but with
  hindsight (and with better observations), could
  spot many more galaxies. It is now thought that
  the Great Attractor is probably a supercluster,
  with Abell 3627 near its center

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sites referenced

• http//archive.ncsa.uiuc.edu/Cyberia/Cosmos/GtAtt
  ractor.html
• http//csep10.phys.utk.edu/astr162/lect/gclusters
  /attractor.html
• http//en.wikipedia.org/wiki/Great_Attractor
• http//www.solstation.com/x-objects/greatatt.htm
  
• http//cow.physics.wisc.edu/ogelman/guide/gr8a/