A Convergence Event (or Convergence) is the final process of a Marker and the affected lifeforms of a given planet or planets.
Throughout the series, "convergence" as described by Unitologists was a vague description of becoming a singular entity or made whole by the Marker. Unitologists sought to preserve the bodies of the deceased in mausoleums or, during a Necromorph outbreak, suicide by apparent suffocation or self-mutilation allowing the lifeform to take over their bodies.
In reality, Convergence is a process triggered by a Marker, when a large enough amount of organic matter has become infected with the Necromorph pathogen. At this time, the Marker will pull all the infected tissue into the stratosphere, where it will form a Brethren Moon and absorb the Marker that created it, along with absorbing the organic tissue of the creators of said Marker.
Once a Convergence Event is initiated with large numbers of Necromorphs present at the Marker, the Marker flashes brightly and emits a fog horn-like sound. Powerful thrusts of wind fling Necromorphs into the air and above the Marker , creating the first pieces of the Brother Moon. Chunks of nearby planets and asteroids are caught and collected in its gravitational pull as the moon grows larger and larger. Once the Brother Moon is completed, the creators of the Marker must be killed and absorbed into the sentient moon in order to feed on organic life throughout the galaxy.
A Convergence Event can be stopped either by the destruction of the Marker that triggered it or by the destruction of the incomplete Brother Moon itself. In the case of the moon above Tau Volantis, a machine powered by a Codex destroys the Moon and its signals.