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Context

• Astronomers have captured four images of the same background supernova being gravitationally lensed by the immense gravitational well of the foreground supernova.

What is gravitational lensing?

• In November 1915, Albert Einstein published his theory of general relativity. A key point in his theory is that massive objects distort the fabric of space-time, the way a bowling ball on a trampoline would stretch and warp the fabric around it. In order to prove Einstein’s theory right, scientists traveled the globe to be under the solar eclipse of 1919.
• There they witnessed the sun bending the light of background stars by the amount Einstein predicted. Nowadays, scientists use the same concept – gravitational lensing – to learn more about galaxies and quasars in the early universe.
• Gravitational lensing occurs when massive foreground objects, such as the two galaxies in the above image, bend and warp the fabric of space itself. The more distant light of the quasar – a young active galaxy – traveling toward us reaches this warped space, which then acts as a lens, bending and magnifying the light. This is why we see a ring with the four different points of light from one bright, very distant light source.

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