The warps in space that make Einstein's perfect cosmic accident | New Scientist
https://www.newscientist.com/...6168-the-warps-in-space-that-make-einsteins-perfect-cosmic-accident/
Picture a glimmering arc of light, the artefact of a lens made of warped space-time instead of glass. Einstein thought there was “no hope” of observing
these bizarre cosmic illusions, predicted by his theory of general relativity – but we’ve been collecting so-called “Einstein rings” since 1987.
An Einstein ring is not a place to visit but a trick of perspective. Two distant galaxies have to line up just so, or we won’t see it. At its most perfect,
it’s a big, unbroken circle: beautiful and scientifically valuable in equal measure.
A complete Einstein ring is one of the universe’s most accurate bathroom scales – the circle it draws around a galaxy lets us add up the mass of everything
inside. This means they can help solve mysteries as diverse as dark matter and the ancient universe.
We know of only a few dozen arcs that approach a full circle, though. So it seems fair to ask: of the Einstein rings we’ve found hidden in the sky so far,
is there one that rules them all?
