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This is a series of books about an interstellar human civilization. After losing a few colonies to unknown reasons, Humanity comes across these rogue asteroids traveling through space. They are made up of two parts traveling at slightly different speeds. In time when they catch up to each other, there is a huge explosion. By third or fourth book the protagonist figures out this is just some kind of fireworks display setup by aliens.
I remember it having a 70s/80s feel when I read it.