The Great Attractor
Detailed observations of the galaxies around us indicate that there is
superposed on the Hubble flow a large-scale streaming motion of about
600 km/s in the general direction of the constellation Centaurus.
A River of Galaxies
This
mass migration includes the Local Group, the Virgo Cluster, the
Hydra-Centaurus Supercluster, and other groups and clusters for a distance
of at least 60 Mpc up and downstream from us. It is as if a great river of
galaxies (including our own) is flowing with a swift current of 600 km/s toward
Centaurus.
Location of the Great Attractor
Calculations
indicate that
about
1016-1017
solar masses
concentrated 65 Mpc away in the direction of Centaurus would account for this
great galactic migration.
The mass concentration responsible for it has been dubbed the
Great Attractor, and may be the largest mass concentration known in the Universe.
Detailed
investigation of that region of the sky, which is near the
galaxy cluster
Abell 3627 shown in the above image,
finds ten times too little visible
matter to account for this flow. This implies a dominant gravitational
role for unseen or dark matter.
Thus, the Great Attractor is
detectable by its gravitational influence,
but the major portion of the mass that must be there cannot be seen in our
telescopes.