A flash of light detected about a mile below the South Pole likely solves a century-old cosmic mystery—and potentially opens up a new kind of astronomy involving ghostly subatomic particles called neutrinos.

In the early 1900s, physicist Victor Hess discovered that Earth is being constantly bombarded by energetic particles coming from outer space, which we now call cosmic rays. Since then, scientists have been hunting for the astrophysical accelerators responsible for hurling the most tremendously energetic of these particles across the cosmos.

Most cosmic rays, though, have an electrical charge, and their paths get bent by the magnetic fields scattered throughout space, making it difficult to follow their footsteps home. That’s why now, the hunt has focused on neutrinos, chargeless