The Shape of Things to Come

With so many bright lights out there, it’s a veritable surprise when we remember that most of intergalactic space is utterly empty. It contains about 1 particle per cubic centimeter on average.

Amidst the cornucopia of stars and galaxies sits a distant cluster of galaxies that exhibits a very notable behavior.  RX-J2248 (named for the ROSAT X-ray telescope, with which it was discovered) lives at a redshift of 0.35 and has hundreds of red old galaxies, as well as a massive amount of dark matter.

If we zoom in (inset, lower right), we can see the effect that this large amount of matter has on its immediate surroundings and on the fabric of space-time itself. In the center of the inset lies a yellow-ish, beautifully glowing bright central galaxy; this is the hub of RX-J2248. While most of its neighbors shine with a very similar hue, others are as blue as a clear daytime sky. These blue objects are actually distant galaxies, and don’t reside very near the cluster at all. They live far behind it, farther away from us and at higher redshifts.

So how can we see these galaxies? The cluster (galaxies, dark matter and all) has distorted space time: the light will still travel in a straight line, but this straight line is now in curved space. This is similar to how lenses in your eyeglasses distort images and bend the paths of light rays. For this reason, this peculiar phenomenon is called ‘gravitational lensing.’

This image represents the shape of things to come as the Dark Energy Survey gears up to begin its five-year mission. With strong gravitational lenses like RX-J2248, with thousands of supernovae and millions of galaxies and galaxy clusters, we will have the power to explore the nature of dark energy and its impact on our universe.

Written by: Det. B. Nord [FNAL]

Image created by: Nikolay Kuropatkin & Martin Murphy [FNAL]