Interstellar space is not empty: it is filled with tenuous gas, which is warm in some places and cold in others. The boundaries between such regions resemble the walls between soap bubbles. When an ultra-energetic particle, a cosmic ray, hits such a wall, the magnetic field there changes abruptly, and the particle bounces off like a ball off a wall.
Scientists tracked millions of such particles in a computer model of the Galaxy. It turned out that cold, dense clouds act as traps: inside them, particles can barely move. But in the warm, tenuous medium, they glide freely along tangled magnetic field lines, like along winding paths. On average, this speeds up their journey through the Galaxy.
This picture helps us understand where particles with energies millions of times greater than those in the Large Hadron Collider come from. Perhaps their sources, exploded stars or black holes, are closer than previously thought.
A cosmic ray with an energy of 1 PeV carries as much energy as a tennis ball moving at 60 km/h, but packed into a single subatomic particle.
In the series "Star Trek," cosmic rays sometimes knock out ship systems — in reality, they do pose a threat to electronics and future interstellar flights.