An “Einstein Cross” is a rarely seen cosmic configuration, in which the light from a distant galaxy is bent by the gravity of galaxies in front of it, creating four images. But scienitsts have found an extra image in an Einstein Cross -- a fifth point of light. This, they found, pointed to “something unusual,” which turned out to be a massive, hidden halo of dark matter. The existence of this invisible structure could only be inferred through careful computer modeling and analysis. The discovery, made by an international team is now being published in The Astrophysical Journal.

Muography can provide a noninvasive approach to examining subterranean infrastructure, and in the Journal of Applied Physics, researchers apply this technique to the Shanghai Outer Ring Tunnel, which runs under the Huangpu River. Using a combination of a spatial scan over the length of the tunnel and a simulation of muons passing through a simplified tunnel model, the researchers mapped the thickness of the sediment. They took 10 minutes of data per location at 50-meter intervals as proof of their technique.