Great Attractor

? © Renée C. Kraan-Korteweg and
Ofer Lahav, Scientific American
(October 1998): pp. 50-57
(Permission being sought)

Larger map.


The Great Attractor is located
in a region of the universe that
is obscured from observers in
the Solar System by the dust of
the Milky Way's disk (more).

The Great Attractor is apparently pulling in millions of galaxies in a region of the universe that includes the Milky Way, the surrounding Local Group of 15 to 16 nearby galaxies and larger Virgo Supercluster, and the nearby Hydra-Centaurus Supercluster, at velocities of around 600 (in the Local Group) to thousands of kilometers (or miles) per second (Lynden-Bell et al, 1988; and Dressler et al, 1987). Based on the observed galactic velocities, the unseen mass inhabiting the voids between the galaxies and clusters of galaxies is estimated to total around 10 times more than the visible matter in this region of the universe and so must be composed of mostly dark matter. Calculations indicate that the Great Attractor has perhaps around 5.4 times 10¹⁶ Solar-masses. Galaxies located on the other side of the Great Attractor are also being pulled in its direction, so that they were being held back very slightly from expanding as fast as rest of the universe, by the gravitational pull of the Great Attractor (Renée C. Kraan-Korteweg, 2000). [More discussion of how the sheets, filaments, and stars of the early universe developed from quantum fluctuations and the gravitational condensation of dark and ordinary matter can be found in First Stars.]

© Renée C. Kraan-Korteweg and Ofer Lahav,
Scientific American (October 1998): pp. 50-57
(Permission being sought)


Larger map.



Millions of galaxies may be moving towards
the Great Attractor, including the Virgo and
the Hydra-Centaurus superclusters of
galaxies (more).

The core of the Great Attractor lies within the so-called "Centaurus Wall" of galaxies. From the perspective of observers in the Solar System, this Great Wall-like structure is viewed edge-on (Woudt and Kraan-Korteweg, 2000). The intersection of the Centaurus Wall and the Great Attractor includes the Norma Cluster or Supercluster -- ACO 3627, Abell 3627, or A3627 (Woudt et al, 2000, 1999a, and 1999b). Indeed, the Milky Way, the Local Group, and the surrounding Virgo Supercluster, as well as the Hydra-Centaurus Supercluster, appear to be part (or at least "appendages") of the sheet of ordinary and dark matter that forms the Centaurus Wall. [More discussion and color images of the Virgo Supercluster and the Centaurus Wall are available from Professor Anthony P. Fairall's lecture on "Large-Scale Structures in the Universe.")

© Anthony P. Fairall,
An Atlas of Nearby Large-scale
Structures, from Large-scale
Structures in the Universe
(Used with permission)




Larger map.




The core of the Great Attractor
("A3627" at left) lies within the
"Centaurus Wall" of galaxies
(more maps and discussion
on Large-scale Structures in
the Universe).

The Great Attractor's core region appears to be dominated by the Norma Supercluster, a highly obscured, nearby, and massive group of galaxies close to the plane of the Milky Way (Woudt et al, 1999a and 1999b; Kraan-Korteweg et al, 1996; and Patrick Alan Woudt, 1998 PhD thesis). In the absence of the obscuring effects of the Milky Way, the Norma Supercluster would have appeared as prominent as the well-known Coma Cluster or Supercluster, but nearer in redshift-space. Indeed, spectroscopic observations support the idea that the Norma Supercluster is the dominant component of a "Great Wall"-type of structure and is comparable in size, richness and mass similar to Coma in the northern part of the Great Wall (Woudt et al, 2000; and 1997). [The Norma Supercluster is also associated with a "Finger of God effect" in plots of galactic redshift velocities when viewed from the perspective of the Solar System.]

© Renée C. Kraan-Korteweg, Patrick Alan Woudt,
and Patricia A. Henning, 1997 (PASA, 14:1)
(Permission being sought)


Larger image with x-ray contours.



The core of the Great Attractor appears to include
the Norma Supercluster of galaxies (more).

The overdensity of galaxies in the region of the Norma Supercluster was first detected in the 1980s. Although astronomers have since observed a large excess of galaxies with optical and infrared telescopes in this region, no dominant cluster or central peak has been identified. This strongly suggests that a significant fraction of the Great Attractor's overdensity could still be obscured by the Milky Way, possibly in another rich cluster of galaxies around the strong radio-source PKS1343-601 (Woudt and Kraan-Korteweg, 2000).