Exploring the monstrous creatures at the edges of the dark matter map

The interior of the Axion Dark Matter eXperiment (ADMX).

ADMX collaboration/University of Washington/LLNL

Scientists are explorers by nature, and when the edges of their maps are terra incognita, researchers sometimes must give names to phenomena for which we have little knowledge. Sometimes those names linger after we know exactly what an unknown quantity is; X-rays are a classic example. The “X” initially referred to mystery, but by the time physicists determined they were simply a high-energy form of light, the name had stuck.

Dark matter, however, is still a placeholder term. Over the decades since astronomers determined that most of the mass in the cosmos is invisible, researchers have done a much better job of figuring out what dark matter isn’t than what it actually is. We know it must be electrically neutral, and it can’t be made up of ordinary matter (electrons, atomic nuclei, etc.). And while “dark matter” itself is a general term, physicists have a sort of cartography of hints: areas on the map in which various dark matter candidates reside.

The most popular of these realms contains the WIMPs: weakly interacting massive particles. Like the term “dark matter," WIMP is generic: the name describes the energy scale at which these hypothetical particles interact with ordinary matter, which in turn reveals something about their mass.