Lemelisk: And you have no theory about what became of the Celestials?

Bowen: All we have are a few guesses — and some secondhand sources that are little better than legends. The grimoiries of the Gree Enclave say the work of the Ancient Masters — the Celestials — was undone by two curses unleashed by the Soul Hunters, whom we identify as the Rakata. The Gree name those curses the Gray Swallowing and the Faceless Mouths, and further refer to them as the Hollowers of Beings and the Eaters of Worlds.

 -Star Wars: The Essential Guide to Warfare Author's Cut — The Celestials on StarWars.com
https://www.starwars.com/news/star-wars-the-essential-guide-to-warfare-authors-cut-the-celestials