Dark Matter Gets a Little Darker

UGC 12591 is the fastest spinning spiral galaxy known, with stars orbiting the center about twice as fast as in the Milky Way. Stellar orbital speeds-in this galaxy and pretty much every other-are too fast; without additional gravity from a great deal of unseen dark matter, galaxies shouldn't be able to keep their stars from flying away. CREDIT: NASA, ESA, Hubble
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.
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