Want to see to the ends of the universe?

Then stick a galaxy in way

It might seem counterintuitive, but the best way to see an object hiding in the most distant recesses of the cosmos is to make sure that you have a nice big galaxy nearby that completely blocks your view.
Confused? Well, in the weird world of astronomy, not only can you see a distant object parked squarely behind a massive galaxy, but you can see it bigger and brighter than you could by using the even the very best of telescopes. The phenomenon, called gravitational lensing, takes advantage of the fact that massive objects warp the fabric of the universe in such a way that light from a distant object is actually bent around the obscuring galaxy and focused on the other side – much like light passing through a lens.

According to this month’s Astrophysical Journal, a group of scientists have used the gravitational lens technique to not only see a galaxy at the edge of the cosmos, but to use that information to precisely measure the size and age of the universe and see just how quickly it is expanding. The measurement has confirmed the age of the known universe as 13.75billion years (within 175million years) and confirmed the strength of dark energy – the mysterious force responsible for accelerating the universe’s expansion.
Unlike a conventional lens, a gravitational lens creates multiple images of the same object from different angles. This is because the galaxy’s gravity pulls in light from angles that would have seen it travel elsewhere in space (see graphic). These multiple clues provide far more information than a single image. By understanding how long it took for the light that makes up each image to travel along each path and its speed, researchers could calculate how far away the galaxy is, the overall scale of the universe and how it is expanding.

Gravitational lensing also works at smaller scales (called microlensing) and can be used for planet hunting. A nearby star, for example, can be used to infer the presence of planets orbiting stars too distant, or too dim, to image directly and even allows astronomers to figure out the planet’s mass.
The results also seem to confirm that dark energy (much hated by many astronomers) does exist, and that the unseen force is indeed accelerating the universe’s expansion.

This week's graphic – What is gravity? and how gravitational lensing works

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