|What's large and blue and can wrap itself around an entire galaxy?
A gravitational lens mirage.
the gravity of a luminous red galaxy
the light from a much more distant blue galaxy.
More typically, such light bending results in
two discernible images of the distant galaxy,
but here the
is so precise that the background galaxy is distorted into a horseshoe --
a nearly complete ring.
Since such a
was generally predicted in some detail by
Albert Einstein over
70 years ago,
rings like this are now known as
Although LRG 3-757 was discovered in 2007 in data from the
Sloan Digital Sky Survey (SDSS),
the image shown above is a follow-up observation taken with the
Hubble Space Telescope's
Wide Field Camera 3.
Strong gravitational lenses like LRG 3-757 are more than oddities --
their multiple properties allow astronomers to determine the mass and
content of the foreground galaxy lenses.