Hi, thanks! I appreciate your interest greatly!
As far as these bubbles, this is the first time I came across them actually, so thanks for pointing them out to me! I find it interesting that they form perpendicular to the disc of the galaxy. I would expect the disc of our galaxy to be the result of a rotating "black hole" that leads to the disc much the same as the Kuiper belt of our solar system, to the Van Allen belts of Earth and to rings of planets such as Saturn, which would imply our galaxy's central black hole rotates along an axis generally perpendicular to the disc of the galaxy, i.e. parallel to these bubbles. If it were the totality of the electromagnetic field then it would suggest the poles, then, are parallel to the disc of the galaxy which doesn't seem right.
My take would be that particles of the electromagnetic field of our galaxy's black hole traveling out of and into its poles are relatively densely packed (due to converging on the center of gravity) in these regions so as to create a "glow" due to the amount of energy present there. As the particles disperse along their particular trajectories into the whole of the electromagnetic field, their density in more outward regions would decrease and the apparent visual effects would diminish until the particles rejoin again into higher density at the opposite pole so that we may only be able to see such effects "near" the poles, like the auroras of Earth, but not elsewhere.
In this interpretation, I would add that they are not necessarily "bubbles" in an electromagnetic field shape kind of way but may just be regions of the electromagnetic field that are energetically dense (as the electromagnetic field north and south pole regions of the black hole) which appear generally like bubbles and have been interpreted as such. This observational image is a bit less "bubbly" than this artist rendition, for example. The importance of this nuance being that if they are bubbles this suggests a boundary whereas if they are areas of higher density in the electromagnetic field, then those boundaries are less tangible and only a visual result. If they are the electromagnetic field as a whole (as bubbles), then the Figure-8 is perpendicular to the disc of the galaxy which doesn't seem right, but if they are regions of the Figure-8 that depict the poles, then the electromagnetic field would be more in agreement with the shape of the galaxy, so I would strongly lean towards that being the case. Just my initial take on it; I will definitely keep it in mind!
I would also note that it reminds me of the 3dz2 orbital., which I find interesting.
For sure though they are related to the electromagnetic field of our galaxy's black hole and ultimately are the result of gravity. The mainstream interpretations I am reading on this observation are a bit perplexing. From NASA: "The feature spans 50,000 light-years and may be the remnant of an eruption from a supersized black hole at the center of our galaxy." This seems a bit ridiculous to me to assign it to the result of some other object than our galaxy's central black hole. :)