Trove
From Halopedia, the Halo wiki
This Flood-controlled Shield World was a world well outside the spheres of influence of both the UNSC and the Covenant. An artificially constructed Forerunner installation, it was a Shield World originally intended to protect sentient lifeforms from the effects of the Halo Array, though was never used.
The Covenant secured a relic on Harvest, pointing them towards another UNSC colony, Arcadia. Another relic directed them to the location of the Shield World, where the Arbiter hoped to use the Shield Worlds' stored Forerunner warships to crush the UNSC quickly, rather than wage the protracted war that would characterise the Human-Covenant War. To prevent this, the UNSC Spirit of Fire sacrificed its FTL Reactor to create a chain reaction in the artificial sun in the center of the Shield World, destroying it from within.
Despite the fact that the Shield Worlds were created as a haven from the Array and the Flood, the external surface is heavily infested with Flood biomass, with forms of various types freely roaming across the surface. Sentinels are a rarity on the outside, but this changes within the center, where the many Forerunner constructs work to prevent the Flood from claiming the interior as well.There also seems to be an Active Forerunner AI in the Shield World as it designates the targets for the Sentinels that are on the Spirit of Fire [1][2].