Extreme Energy Cosmic Rays

There's UHECRs and then there are UHECRs. This is a story about the latter. Cosmic rays are electrically charged particles that careening in from deep space to bombard the Earth. These shouldn't be confused with the particles from the sun - solar wind - or even cosmic neutrinos. Cosmic Rays are almost entirely made up of atomic nuclei that have been stripped of their electrons, and accelerated into space. That means mostly protons, but occasionally we see Helium, Carbon and Silicon nuclei as well.

UHECRs are cosmic rays that smash into Earth's atmosphere with alarmingly high energy. A particular class of Extreme UHECRs have baffled astrophysicists for two decades. The first of these, the so-called "OMG particle" was measured to have the kinetic energy of a gallon of milk falling from your refrigerator shelf. That's quite a bit for a single particle.

Natalie Wolchover reported this week on recent progress in understanding the origin of these beasts in Quanta Magazine. The article comes complete with an interactive, dens map of the nearby universe. As Wolchover notes, to accelerate a particle to that velocity, they'd need a particle accelerator the size of Mercury's orbit around the sun.

Proposed mechanisms for generating these particles have met with recent theoretical progress suggesting that whatever intergalactic monsters are able to accelerate such particle, they shouldn't be altogether uncommon. This comports with long standing observations that particles with such energies must be "young". As with any charged particle, these extremely fast UHECRs are still deflected by our galaxy's magnetic fields and subject to the friction induced by the cosmic microwave background.