Do gluon jets occur spontaneously in the real world, or only in a particle accelerator? In this article by Matt Strassler, he says "A struck quark, like any accelerated particle, will radiate.  A suddenly accelerated quark will radiate many gluons.  So what actually emerges at the edge of the proton is not a fast quark but a collection of fast gluons along with the fast quark.  The shape of the jet is actually determined mainly by the way that the gluons are radiated before the quark even emerges from the proton."
Is this something that occurs spontaneously in the real world, or only in a particle accelerator?
I find this to be an issue in many science papers, where they do not mention if what they are describing only occurs in a lab.
 A: Extremely high-energy cosmic rays, when they strike the Earth's atmosphere, spontaneously cause many of the reactions that we normally see only in particle accelerators, and in particularly high-energy cases it would not at all be surprising to see a gluon jet. In fact, their energy is often orders of magnitude higher than we can produce in particle accelerators. The highest-energy cosmic ray possessed something like 320 EeV, or equivalently 320 million TeV, of energy, while the LHC produces collisions with a center-of-mass energy of a measly 13 TeV in comparison.
As far as actually directly observing a gluon jet from a cosmic-ray interaction in the upper atmosphere, the main problem is that we don't really have too many particle detectors that are just sitting in the upper atmosphere, at a spot where a high-energy cosmic-ray interaction happens to take place. So we inevitably observe these reactions from a significant distance, which means the short-length characteristics of the reaction are often obscured by the resulting particle shower as the products of the reaction hit other particles in the atmosphere, dispersing their energy over a wider and wider cone.
