The sphere at the center of the ark
I do not know if it is the Maginot sphere, or perhaps the mantle, at the center of the ark but I believe the mantle is a device left behind by a race called the predecessors. I think the Forerunner found this ancient device and began to worship 100,000 years ago before they decided to try and use it in an attempt to advance like the ones who obviously "acceded to a higher plane" before them. I think the mantle is a device designed to be an evolution machine but with the unfortunate byproduct of creating of the flood. I think after the Forerunner realized the flaw of the device they learned to reverse it into a "devolution beam" to destroy the flood.
My sources are my interpretations of the terminal messages like the one where the Life Form communicates to the Mendicant Bias and small clues while playing halo games.
The sphere in the center of the ark clearly has some odd properties. One thing I found odd was during one of the first cut scenes where the core is visible I noticed weird linier lines flashing in a way that made it seem like there was more than 3 dimensions within the field around it. I also noticed it has an almost crystalline structure. This led me to believe this could be made of the odd crystals that are supposed to bend space and time. Maybe the halos are designed to matrix out this special rupture to either chance or “vacuum up this galaxy”. It would also make sense that this could be a Dyson sphere, or entrance to a Dyson sphere inside some sort of special rupture. Maybe this rupture is what powers the halo effect? I do know that inside the ark of the covenant (“reality”) it hold the word of god and that could be what the ark means in the halo reality… where the forerunner put the artifacts of their god.
If the flood ended up being what the forerunner worshipped it would make sense that that is why MB turned.
P.s. I might have been testing the peculator while I wrote this.
I Think this is the next up flood form