Omega molecule

An Omega molecule is a short-lived, highly unstable molecule theorized to have existed in nature at the instant of the Big Bang. It is believed that, if artificially recreated, an Omega molecule would be the most powerful substance in the universe, capable of powering an entire civilization.

A single Omega molecule was synthesized in 2268 by Federation physicist Dr. Bendes Kettaract. It remained stable for a fraction of a second before exploding, killing 127, destroying the research station and rupturing subspace for several light years in the Lantaru sector, making warp travel and subspace communications impossible. 

It was later determined this incident was orchestrated by an assimilated Vulcan named T'Urell. He was able to stabilize an Omega molecule and used it to power a Borg sphere, which was destroyed by James T. Kirk. Kirk thereafter recommended the establishment of the Omega Directive, ordering the destruction of Omega molecules whenever discovered, and limiting knowledge of the molecule to starship captains and flag officers. (video game: Star Trek: Legacy)

The Borg learned of the Omega molecule (known to them as "Particle 010") through the assimilation. They regarded Omega with near-reverence, believing it to be a perfect and flawless substance. They were able to synthesize a single molecule, which destroyed 29 Borg vessels with 600,000 drones when it destablized. All Borg were ordered to assimilate any Omega molecules found.

In 2374, the USS Voyager discovered a civilization in the Delta Quadrant which was successful in synthesizing some 200 million stable Omega molecules. 

In 2376, the Borg, led by a clone of Locutus, attacked the Federation, Klingon Empire, and Romulan Star Empire in an attempt to obtain an Omega particle. They were eventually stopped and destroyed by the USS Enterprise (NCC-1701-E). (video game: Star Trek: Armada)