#gzk

What Are The Most Energetic Particles In The Universe?

“The fastest protons — the ones just at the GZK cutoff — move at 299,792,457.999999999999918 meters-per-second, or if you raced a photon and one of these protons to the Andromeda galaxy and back, the photon would arrive a measly six seconds sooner than the proton would… after a journey of more than five million years! But these ultra-high-energy cosmic rays don’t come from Andromeda (we believe); they come from active galaxies with supermassive black holes like NGC 1275, which tend to be hundreds of millions or even billions of light years away.”

When it comes to the Universe, you might think that energy really is only limited by rarity: get enough particles accelerated by enough supermassive, super-energetic sources, and it’s only a matter of time (and flux) before you get one that reaches any arbitrary energy threshold. After all, we’ve got no shortage of, say, supermassive black holes at the hearts of active galaxies. And yes, we do find cosmic rays hundreds, thousands or even millions of times the energy that the LHC can achieve. But when we think about the Universe in detail, these cosmic rays aren’t unlimited in their energy, but are rather stopped in their tracks by the most unlikely of sources: the ultra-low-energy cosmic microwave background, left over some 13.8 billion years after the Big Bang.

Cosmic Rays & the Cygnus Mystery

C O N T E N T S: KEY TOPICS They identi? ed distributed emission of gamma-rays over the energy range of 1 to 100 GeV in the Cygnus X region of the sky with a “cocoon” of freshly accelerated cosmic rays.(More…) Recently observed radio silent quasars that emit gamma rays with enormous intensity may account for the origin of cosmic ray flux at energies that exceed 10 16 eV. Other galactic sources…