Our planet is constantly bombarded by high-energy particles from space—a phenomenon known as cosmic radiation. While the term sounds frightening, most of this radiation is harmless. It includes visible light and subatomic particles streaming through the cosmos, often referred to as cosmic rays. Some originate from our Sun, others from within the Milky Way, and a surprising number travel vast distances from other galaxies.
The Scale of Extragalactic Impact
It’s remarkable that Earth routinely intercepts particles from galaxies millions of light-years away. These particles lose energy over time, but some still arrive with extraordinary force. Their energy is measured in electron volts (eV), a tiny unit—26 million trillion eV equals just one joule (the energy to warm a cubic centimeter of water by 1 degree Celsius). Yet, cosmic rays often carry mega-electron volts (MeV) or even giga-electron volts (GeV).
However, some cosmic rays defy expectations. In 1991, the Fly’s Eye detector recorded a particle with an energy of 320 quintillion eV, or 320 billion GeV. This “Oh-My-God” (OMG) particle possessed 51 joules of kinetic energy—equivalent to a slow curveball, but concentrated into a single subatomic particle.
What Makes This Particle So Strange?
Protons, the fundamental particles making up this ray, are unimaginably small. To put it in perspective, a proton compared to an orange is like an orange compared to Neptune’s orbit. The OMG particle was moving at 99.9999999999999999999995% the speed of light. Had it been racing a photon since the universe’s birth, it would be just 600 meters behind today.
Where Does This Energy Come From?
The source is likely supermassive black holes in distant galaxies. These black holes eject powerful beams of matter and energy, carrying strong magnetic fields. Charged particles, like protons, accelerate within these fields. Collisions between gas clouds further boost their energy through a process called “first-order Fermi acceleration”—a cosmic trebuchet flinging particles at near-light speeds.
The second-highest-energy cosmic ray ever detected, nicknamed Amaterasu, came from the galaxy PKS 1717+177, known for its powerful jets. These events are so energetic that they dwarf anything we can create on Earth.
A Violation of Cosmic Rules?
However, the OMG particle challenges our understanding of physics. The universe is filled with the cosmic microwave background—low-energy radiation left over from the Big Bang. At near-light speeds, particles encounter this radiation amplified by the Doppler effect. This should slow them down, or even break them apart into other particles.
Yet, the OMG particle reached us despite these obstacles. The solution may be that it wasn’t a proton, but a heavier nucleus—like iron—which interacts differently with the cosmic microwave background.
A Window Into the Early Universe
The existence of these ultrahigh-energy cosmic rays proves that extreme energy sources exist beyond our galaxy. It’s like having a glimpse into the fraction of a second after the Big Bang. The universe is constantly revealing its secrets, and these particles are just one way it does so.
