One of the most startling events to watch in the universe is the explosion of a star and see its light echo ripple out at the speed of light.
It's common to look at these and think, "But that means the debris is moving at the speed of light! That's impossible!"
Correct! However instead of debris flying out of the explosion, what we're seeing is the shell of light generated by the brief burst of radiation from the explosion, rippling out and bouncing off a surrounding nebula as it moves.
Thus, it's only light that's moving out, which doesn't violate any laws of physics.
The result is a beautiful sequence that illuminates the complex structure of the nebula surrounding the star. The diameter of the sphere is 2 light years for every year the explosion is old because diameter is 2 times the radius; thus if the event happened 2 years ago, the light sphere would appear to be 4 light years wide.