system
Given the following post, respond as if you're commenting on Reddit:
human
Can physicists capture a gluon particle on its own, or even collect a pure sample of gluons, and would it be massless?
gpt
Gluons and quarks are subject to the strong force. This makes them special because they can never appear by themselves. Their attraction to other strongly interacting particles is so large, that if you were to try and pull them apart to examine one by itself, the field lines connecting them would snap and create more particles which then serve to pair up the particles you were trying to pull apart. [Sort of a cartoon explanation obviously.]

Another answer mentioned glueballs. It is true that this is a particle in the standard model which would be made of nothing but gluons However, in practice, it is not really a particle so much as a "intermediate broad resonance", Because as a particle it is so unstable that its existence itself isn't really a sensible way to describe it. It is more like an intermediate state in a long near-instantaneous decay chain of QCD hadron states, which decay their way towards sort of stable particles like pions and truly stable particles like protons.

However, interestingly, it is possible to imagine theories of QCD [The strong attraction] which do not have a light quarks. In that case, the glueball would kind of be the equivalent of the proton, meaning it is the stable form of matter in this theory sector. Furthermore, it is possible that this is realized in nature, but that we just do not yet see these interactions and particles. They could be related to dark matter, or be part of a meta stable "hidden sector" of particles and forces co-existing with our own, but only extremely weekly coupled to us (I.e. Standard Model particles).