Ring by Stephen Baxter
This review will contain mild spoilers.
The sun is under attack from dark matter entities, causing it to age prematurely. An expedition is sent on a thousand-year round-trip journey in a generation starship to investigate. Due to relativistic effects, the expedition arrives back in the solar system five million years in the future to find the sun is now a red giant and the solar system is destroyed. The expedition finds nearly every star in the universe has prematurely aged, and realising they are the last hope for the survival of humanity the expedition sets off for The Ring, a Xeelee construct, and a new start elsewhere.
This fourth novel in Stephen Baxter’s Xeelee sequence can be considered a sequel to the second instalment, Timelike Infinity, and I would highly recommend that you read that novel first to get the most out of this one. There are also fleeting references to the first and third novels in the sequence (Raft and Flux), but they are minor and do not require you to have read them to enjoy this novel.
Despite its intriguing plot and some well written and likeable characters, this story is let down by the large sections of scientific exposition the reader has to wade through on numerous occasions. If you like reading detailed explanations of stellar nucleosynthesis, stellar evolution and the warping of space-time around cosmic strings, then this book is for you. Anyone else, without a background knowledge of astrophysics, may find it hard going.
One for the hardest of hard SF fans or Xeelee sequence completists.