The Spiral Slayers (Encounters) by Rusty Williamson

On a planet called Amular at the edge of The Great Coma Wall, an alien race called the Loud make contact through Captain Maximus, changing his life forever. The world-shattering impact and political turmoil of the alien contact is only exceeded by what happens when the Loud bestow the gifts they bring. Then an unexpected discovery: something has been coming across the observable universe since the dawn of time and now it is upon them. As the mind-boggling truth is uncovered, it becomes clear that this new alien force intends to destroy Amular while on its way to a far more devastating objective. Neither the Loud nor Amular’s inhabitants can hope to stop this force, and there is no negotiating, no surrender and nowhere to run or hide.