The Andromedan dark-matter entities known as the Pa'anuri are the reason for much of The Milky Way galaxy's history. They have been encountered by many ancient races, generally shortly after that race invented the teraport. Teraporting is injurious to dark Matter Entities, so this first encounter was usually last. The Pa'anuri destroyed all of the solar systems of any civilization that invented the teraport.
The F'sherl-Ganni were thought to be the first civilization to survive inventing the teraport and the Dark Matter Entities finding out about them. The result was a long and bitter war between the two overlaid universes, which eventually ended in a treaty. The Pa'anuri retreated to the Andromeda Galaxy, and the F'sherl-Ganni set up the wormgate network and initiated the infamous copy-and-interrogate policy in order to find and suppress independent invention of the teraport. With the de-extinction of the Oafa 2013-08-25 and discovery of their ancient technology and ships, it became clear that at least one other civilization battled the Pa'anuri, some twelve million of years before the F'Sherl-Ganni did. 2014-02-28 The Oafa fled the war to their 'can full of sky' 2013-04-20 - a vast ship called Eina-afa.
Dark matter does not interact with baryonic matter except gravitationally, which means that the Pa'anuri effectively live in a parallel universe. However, the two aspects can communicate via gravity waves, and also attack each other with gravy. Individual Pa'anuri (they are their own warships) are too large to be significantly harmed by gravy weaponry at our scale, but the tiny wormholes created by teraports can harm them, and they can even be killed by very rapid teraporting or high-density teraport-denial fields.
About 100,000 years ago, a wormgate sent by the Pa'anuri from Andromeda arrived, its purpose being to deliver to the F'sherl-Ganni the plans for a galactic drive engine intended to prevent the Milky Way's eventual merger with Andromeda. The device was completed during the Teraport Wars, but it was a trap; when activated, the "engine" caused the Milky way to pinch itself off as its own little universe, and then began destroying the galaxy from the core out.
It might have been possible to repurpose the wormgates and reverse the anomaly created by the bogus drive, but by the time the anomaly was discovered it was too late to do so. However, the bizarre physics of the anomaly allowed Captain Kevyn Andreyasn to use the Andromeda wormgate as a time machine, taking him back to before the "engine" was activated. Once he had done this, he convinced the Fleetmind of the danger, and the Fleetmind in turn gathered a coalition fleet and headed to the Core.
Kevyn and the Fleetmind convinced the F'sherl-Ganni not to activate the engine, but the Pa'anuri who were observing began to attack. This so-called Core War took a heavy toll in the fleet, but it bought time to create a giant teraport-denial field that killed every Pa'anuri in the galaxy. The Fleetmind promptly stole the entire coalition fleet, settled into the dominant personality of Petey, rebuilt the engine into a power source, and took the war to Andromeda. The war there is still raging and the Pa'anuri have built their own core generator that is 35 times larger than the one in the Milky Way 2010-11-27.
The word Pa'anuri (or possibly Paan'uri) comes from a F'sherl-Ganni phrase meaning "That gravitic anomaly is giving me the willies". The Pa'anuri have their own language, in which they call themselves US and beings made of baryonic matter ANNOYING [footnote, 2005-07-10].
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