Explanation:
What's large and blue and can wrap itself around an entire galaxy?
A gravitational lens mirage.
Pictured above
on the left, the gravity of a normal white galaxy has
gravitationally distorted
the light from a much more distant blue galaxy.
More normally, such light bending results in
two discernable images of the distant galaxy,
but here the
lens alignment
is so precise that the background galaxy is distorted into a nearly complete ring.
Since such a
lensing effect
was generally predicted in some detail by
Albert Einstein over
70 years ago,
such rings like SDSSJ1430 are now know as
Einstein Rings.
SDSSJ1430 was discovered during the
Sloan Lens Advanced Camera for Surveys (SLACS)
campaign, an observation program that inspected lens candidates found by the
Sloan Digital Sky Survey (SDSS)
with the Hubble Space Telescope's
ACS.
Strong gravitational lenses like SDSSJ1440 are more than oddities -- their multiple properties allow astronomers to determine the mass and
dark matter
content of the foreground galaxy lenses.
Given these determinations, SLACS data has now been used, for example, to show that
dark matter fraction
increases with overall galaxy mass.
The
inset images
on the right depict, from top to bottom, a computer reconstructed image of what the background blue galaxy really looks like, just the white foreground galaxy, and just the lensed blue background galaxy.
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