15th October, 1991 the University of Utah's "Fly Eye" cosmic ray detector produced an "off-the-charts" reading. A single cosmic ray with the energy of a baseball thrown at 58mph.
That may not seem like very much - even a small meteor hits the ground with more energy than that. But cosmic rays are sub-atomic particles. This one was probably just a single iron atom, stripped of all of it's electrons - hurled by some unknown event from the direction of Ursa Major (aka "The Great Bear" - which includes "The Big Dipper").
A single atom would have to be going extremely fast to carry as much energy as the 500,000,000,000,000,000,000,000,000 atoms in that 58 mph baseball! So fast that the Theory of Relativity would make it much heavier than it would ordinarily be.
This particle is by far the fastest material object known to mankind...which is why the Fly Eye team named it "The Oh-My-God! Particle".
This iron atom would be going very close to the speed of light...99.999999999999999999999510%. So close that if you had race between it and a light beam lasting a quarter of a million years - the light beam would cross the finish line only a centimeter ahead of OMG.
We don't know what caused the OMG to be flung so fast in this direction - there are no known astronomical processes that could do it. Furthermore, we know that it could only have come from a source within either our galaxy - or some other nearby galaxy. Beyond that kind of distance, it would have been slowed down by interactions with the remaining after-glow of the Big Bang. Because the particle is only gradually catching up with light from the event that caused it, you'd expect we'd have seen the flash of light or radio waves from whatever astoundingly violent event produced it - but we do not.
Subsequent experiments show that a particles with this much power, coming from the general direction of Ursa Major hit the earth about once every minute.
You might wonder what would happen if you were hit by one...after all, something with the force of a 58mph baseball would certainly sting!
But what you have to remember is that although there is a lot of energy here - it's being delivered by something considerably smaller than an atom. So all that energy would pass right through your body - probably without hitting anything along the way. If it did happen to hit one of your atoms - it would surely smash it to pieces - and the pieces would go shooting off at similarly insane speeds - and the odds of one of those hitting anything would also be very small. So most of the energy from the particle would simply spray out in all directions - gradually dissipating in more and more collisions.
Personally, I'll never be able to look at Ursa Major again without a tendency to flinch!