The Scourge is the colloquial term for a huge and extremely dangerous interstellar phenomenon sighted across much of the Heleus Cluster. It appears to be a cloud spreading in "tendrils" that affect planets and surrounding space, destroying starships that attempt to pass through or near it.
The Scourge is aggressively drawn to Remnant structures on planets, though the cause of the attraction is not yet fully understood. This manifests as further "tendrils" of dust and radioactive particulates that cling to the surface of Remnant technology and interfere with its operations. Either this matter was left behind after the planet in question passed through the Scourge itself, or even distant interactions with Remnant technology can cause the Scourge to coalesce spontaneously. In either case, even this minor manifestation of the Scourge demands additional caution when approaching Remnant sites.
No long-range data showed any sign of the Scourge before departure to the Heleus Cluster. Nexus scientists suggest it must have appeared in the intervening centuries while the arks traveled to Andromeda.
One of the Scourge's more interesting characteristics that it appears artificial. Its origin point is yet to be determined, but the pattern of the 'tendrils' and the composition of the cloud could not have been caused by any celestial event known to astrophysics. Investigations are ongoing, though slowed by the deadly conditions created by the Scourge.
We now know the Scourge is the fallout of a weapon detonated at Khi Tasira. Doctor Aridana believes the weapon caused an instantaneous cluster-wide warping of space-time, briefly connecting multiple points in the Heleus Cluster at once.
Her models suggest the warp effect annihilated multiple planets, forming the debris in the Scourge's tendrils, while the resulting radiation converted much of that debris to element zero. As we have seen, the space-time warping effect continues on a micro scale within the Scourge to this day.