Omega

I think they come from through the event horizon, of a black hole, where omega was trapped once

Omega sends the silents to our universe with a purpose, which is to be reborn as omega, the only way to do this, is through a new born child, and this child is the impossible astronaut

The silents take omega last bodily essence, and place it in amy unborn child, and once the child is 6 month, the slent take the child and place it in the space suit

The space suit serves a purpose, it is aids the growth of the timelord cells, so one day, the child regenerates into omega

Like the master, we wont see the regeneration, until the series finalie

Omega learns how to create and control "the effect" a space/time anomaly that allows him to rewrite history. The novel also established the existence of Omega's wife, who after his accident became the Doctor's wife and the mother of his thirteen children. After she was shot in the matter universe (in Parkin's Virgin Missing Adventures novel Cold Fusion), Omega rescued her and brought her to his universe.