Perched on the slope of a volcano in Mexico, the third-highest peak in North America, the High-Altitude Water Cherenkov (HAWC) Gamma-ray Observatory is not a system of lenses and mirrors but a collection of ultrapure water tanks wired up with ultrasensitive light detectors. Whenever a very-high-energy particle from space collides with an air molecule overhead, a spray of subatomic particles rains downward and generates a faint flash of blue light in HAWC’s water tanks. It just so happens that—in theory, at least—dark matter particles that collide with one another or decay should produce very-high-energy gamma rays capable of triggering this event.

VIEW THIS ARTICLE