There is a direct relationship between this thread and the following tread: "What is a feasible way to generate an Atom?".
http://www.spacebanter.com/showthread.php?t=196513
In both, we are relating to Spiral galaxy with significant indication of Hydrogen.
Let's start with the following statement about the core of the Milky Way galaxy:
" The bar may be surrounded by a ring called the 5-kpc ring that contains a large fraction of the molecular hydrogen present in the galaxy, as well as most of the Milky Way's star formation activity."
Why the bar contains large fraction of the molecular hydrogen present in the galaxy??? How come??? Where this huge molecular hydrogen come from???
This is a strong indication that the rotational suppermassive black hole in the core of the spiral galaxy has the requested power for Atom Creation activity!!!
This Idea perfectly fits and explain the source of the the hydrogen "bridge" between Andromeda Galaxy and the Triangulum Galaxy.
As both Andromeda and Triangulum are Spiral Galaxies, with rotational suppermassive black hole, they should have the requested power to generate Hydrogen Atoms in their core.
Therefore, as they are drifting apart, they are Releasing Hydrogen and set this kind of bridge!!!
This is a significant element in our understanding of the universe!!!