Scientists have just released details on their discovery of inter-galactic baryon material - "Dark Matter" that turns out to be regular matter, except that it is 'dark' - dispersed throughout the inter-galactic spaces and therefore not hot enough to detect. Sort of like it is all black-body radiation at very low temperatures.
It could be a considerable amount of material.
Previously, it was assumed that inter-galactic space was empty, devoid of any usable resources.
My question is, 'By what means could this baryonic material be collected by a mega-huge multi-generational ship that has been sent on a one-way mission to spread humanity throughout the universe, in sufficient quantities to replenish supplies?'
Consider that the recent collision between two neutron stars, that produced the most recently-detected gravitational waves, probably created elements as dense as gold and platinum. Very useful elements to go after.
It would have to be collected very slowly, atom by atom, maybe even baryon by baryon.
Further referenes to describe the scope, are Half the universe’s missing matter has just been finally found and MYSTERY OF THE UNIVERSE’S MISSING MATTER FINALLY SOLVED BY SCIENTISTS Which explain that this matter is concentrated in filaments between galaxies, up to six times greater density than normal. These filaments or strands would form the path that such an intergalactic ship would follow, like mining a mineral seam on Earth. And since they are filaments stretched between galaxies, they could easily be material pulled FROM the galaxies, in a 'bridge' between them. All bets as to the elements in them are off, if this is so.
As for dark matter being something different that regular matter, all bets are also off.
Strangely familiar: Is dark matter normal stuff in disguise? from August 2015
IT’S matter, but not as we know it. In July, an unexpected visitor appeared at CERN’s Large Hadron Collider near Geneva, Switzerland. Dubbed the pentaquark, this peculiar particle represents a fundamentally new way to aggregate the basic building blocks of matter. Although not forbidden by our current understanding of how stuff comes together, it had never been conclusively spotted before.
He even argues that ordinary matter in extraordinary formations could solve one of the greatest cosmological mysteries of our time – dark matter.
Ideas about physics that are based on information and theories that are more than ten years old are, well, ancient history.
Contact with those aboard the ship would probably be lost by anyone in our galaxy, and they would be multi-generations before they arrived at their destination, but our 'seeds would be cast', randomly 'blowing in the inter-galactic wind'.