The most intense flashes of lightning can do more than just light up the sky: Lightning sometimes acts as a natural particle accelerator, firing beams of electrons at high speeds toward space, a new study says.

To start the accelerator, a powerful lightning strike needs to coincide with a burst of cosmic rays—high-energy particles coming from space. (See recent pictures of lightning created in the ash plume of an Iceland volcano.)

When cosmic rays enter our atmosphere, they strip electrons off air molecules. If a strong lightning bolt happens at the same time, it acts as an electric field, triggering an electron "avalanche" that launches