sci-fi book that spans about a thousand years. Earth is contacted by robot aliens who trade technology in exchange for information about our religions. The main character is an astronaut

[Luana]

There are many characters throughout this expansive book but it mostly follows a single astronaut who goes out to space for (I don't remember the number but lets say) 20 years of his life but (maybe) 50 years has passed on earth. This happens multiple times.

The book ends with his somehow (and very painfully) fusing with the robot aliens to stop some sort of cataclysmic event that is stopped by the aliens forming a net of some kind around a blackhole or whatever it was that would wipe out all life in the galaxy. 

The aliens were all robots that were made by a previous alien race that had died out long enough in the past that the robots no longer remembered them. They were fascinated with religion because they realized the necessity of self sacrifice to get a civilization to make it past some technological point

[Michele]

Luana do you remember when you read the book, and whether it was new or old at the time? Anythjng about the cover, or any details sbout the astronaut's life?