Y. Son

Dark matter is like an invisible glue that holds galaxies together. It emits no light, but if its particles collide, gamma rays can flash. Scientists hunted for such flashes in dwarf galaxies — small stellar clusters with lots of dark matter and almost no ordinary matter.

A charged particle beam is like a jet of water from a hose: it can be narrow or diffuse, steady or curved. To know exactly where particles are headed, you need a sensitive screen. In the WISArD experiment at ISOLDE, CERN's accelerator, that screen is a compact detector based on microchannel plates.

A spotlight shines ever brighter, but at some limit the bulb suddenly burns out, and no more light comes through. Astrophysicists have seen something similar in the distant blazar Markarian 421. This is an active galaxy whose jet of superheated plasma points almost straight at Earth, like the beam of a cosmic lighthouse.