It is one of the most massive objects in the visible universe.
In this view from the Hubble Space Telescope's
Advanced Camera for Surveys,
Abell 1689 is seen to
warp space as predicted by Einstein's
theory of gravity -- deflecting light from individual galaxies which lie
behind the cluster to produce
multiple, curved images.
The power of this enormous gravitational lens depends on its mass, but
the visible matter,
in the form of the cluster's yellowish galaxies, only accounts
for about one percent of the mass needed to make the observed
bluish arcing images of background galaxies.
In fact, most of the gravitational mass required
to warp space
enough to explain this cosmic scale lensing is in the form of still mysterious
As the dominant source of
gravity, the dark matter's
unseen presence is mapped out
by the lensed arcs and
background galaxy images.
Surprisingly, close inspection of the
has revealed the presence of over 100,000
globular star clusters
in the galaxy cluster.
Hubble Heritage Team