About three and a half million years ago, the center of our galaxy exploded.
This is no exaggeration, no attempt to overstate for effect. There's no need. The event was colossal. The explosive power coming from the core of the Milky Way easily, vastly outshone all the stars in the galaxy combined, sending two huge beams of super-high energy marching out into space in opposite directions. The scale of this event is nearly incomprehensible, and it lasted for 300,000 years.