Is there a connection between gluons and photons? I was wondering if there is any sort of connection between a gluon and a photon since they are both considered massless. 
 A: From the perspective of fundamental quantum field theory, gluons and photons are quite similar. Both of them are gauge bosons, meaning that their existence is required by a mathematical mechanism called local gauge invariance. However, as particles, there isn't any particular connection between them. For instance, there's no reason they both have to be massless. The properties they share (zero mass, zero electric charge, spin one, etc.) are more coincidental than anything else.
A: Gluons and photons are similar in the sense that they are both massless gauge bosons. They do, however, correspond to different gauge symmetries: photons arise due to $\mathrm{U}(1)$ symmetry, while gluons follow from $\mathrm{SU}(3)$. This leads to a different number of particles: there is only one photon, while there are eight different gluons, corresponding to the number of generators of the respective gauge group. Furthermore, gluons are electrically neutral, but they are charged with colour charges, allowing them to self-interact strongly and even form bound states (glueballs). Photons, on the other hand, are simply electrically neutral but do not carry any other charges. 
A: the 9th gluon of the U(3) symmetry is considered a photon. which makes the color symmetry su(3)
