A Hegemonising Swarm, also known as a Hegswarm, was a very large collection of Aggressive Hegemonising Swarm Objects, each a selfishly auto-replicating organism determined to turn every piece of matter it found into copies of itself. Left unchecked, Swarm Objects would eventually turn the universe into nothing but those self-copies. They were a persistent nuisance, in the Culture's experience, although subject to certain mitigations - over and above outright destruction, which was always an option - and smaller groupings, often called Smart Matter, or just smatter, tended to crop up from time to time but were generally cleaned out by the Culture - or one of the other Involved civilizations - much as one would deal with a nest of ants on one's doorstep.
"A Hegswarm?" Nlissa said, sounding aghast.
Full-size Hegswarms were, quite literally, the stuff of nightmares; stories of galaxy-consuming infestations were the kind of tale told to frighten children in darkened rooms. The problem was one of exponential growth: if each Swarm Object could make two or three or more copies of itself in a few days or weeks, after a year you would have quadrillions of the wretched things, at least in theory. So it was really important to stamp out Hegswarm infestations as soon as they were discovered, and to make sure that every last one of the things was obliterated; leaving even one behind meant that you had another nightmare scenario on your hands in a month's time.
"Persistent outbreaks over a large volume," the ship replied sadly, "Which the locals are struggling to control with, to be honest, not particularly effective weapons."
The ship threw up the large screen again, showing a now-familiar view of the Antlia galaxy. The image zoomed and twisted, drawing into focus one of those odd regions where no stars seemed to shine.
"There are huge volumes, like this one, which have no stars, but which nevertheless have considerable mass, judging from the gravitational attraction on other parts of the galaxy," the disembodied voice of the ship went on, "I think thousands, maybe millions of stars and all their planets have already been eaten, turned into Swarm Objects."
"People have died?" Nlissa almost squeaked.
"Almost certainly," the ship said gloomily, "And probably in huge numbers. The weapons blink I've been seeing is generally on the edges of regions like this; probably people desperately trying to protect their own civilizations from incursions of Hegswarm elements migrating from regions they have already converted."
Nlissa held her head in her hands, despair written all over her body.
"Could we help?" she demanded, looking up suddenly, "Could we save lives?"
"We quite definitely could," the ship said immediately, "But, should we?"
"What do you mean?" she insisted, looking horrified.
"If we had the full strength of the Culture, I feel confident we could rid this galaxy of the Hegswarm in no time at all," the ship replied. "Although to be honest we would never have let it get to this state in the first place."
"But, if it's just me - even with a couple of Limited Service Vehicles and the thousands of GCUs I have amassed over the last few hundred years - it might not be possible to counter the Hegswarm," the ship went on, "And we - you and I both - might not personally survive the attempt to do so."
Nlissa was silent, thoughtful.
"So this is the moral choice that Rahanna seemed to predict?" she said, almost talking to herself, "The chance to save uncountable lives - save this entire galaxy from destruction - but at personal risk to everybody on board, Minds included?"
"That's about the size of it," the voice of the *Kainotophilist* replied, now sounding infinitely saddened.
"There'll have to be a discussion, a debate, everybody on the ship," Nlissa said firmly, "And a vote. That’s the Culture way."
"Yes, it is," the ship agreed, "And I have suggestions for mitigations, too, to improve our chances of survival, should it come to that. But, I suspect I already know the answer to the vote."