Physicists don’t know for sure where cosmic rays come from, but they suspect supernovae and powerful black holes are involved. Although we’re bombarded with the particles, the very highest energy cosmic rays are rare. Studying them has therefore been difficult. But it turns out that smartphone cameras are actually good at detecting them.
When these especially energetic rays hit Earth’s atmosphere they create a shower of other charged particles. These particles hit a camera’s sensor, resulting in one bright pixel against a dark background. If enough phones in the same area see particles, scientists can recreate the cosmic ray’s path through space.
You can take part in the project through an app called CRAYFIS (for Cosmic Rays Found in Smartphones). [Daniel Whiteson et al, Observing Ultra-High Energy Cosmic Rays with Smartphones]
CRAYFIS only operates when a phone is plugged into a power source and not otherwise being used, so it will not drain your battery. Imagine: between Candy Crush and Facebook sessions, your phone can help unravel the mysteries of the universe.