The story is about a star that becomes a supernova. A colony on a planet is about to be wiped out from it , but the government keeps it under wraps because they won't be able to evacuate everyone. The main hero and with the help of an alien race that reads minds build a wall around the planet. I feel like this was a book in the middle of the series since they allude to being at war with these aliens but now at peace.
This is Jack McDevitt's The Devil's Eye
It's one of his Alex Benedict books, so it is indeed part of a series.
From the link:
Alex Benedict, interstellar antiquities dealer, and his assistant, Chase Kolpath, are on vacation when they receive a cryptic message from Celebrated writer Vicki Greene, whom neither has ever met, asking for help. But when they return home, Alex discovers that Greene has asked for and been given a mind wipe. She has no memory of her past life or of her plea for assistance. Yet she has transferred an enormous sum of money to Alex. But for what purpose?
To answer that question, Alex and Chase venture to the place where Greene had been vacationing prior to sending her message. It is the most remote of human worlds, literally outside the galaxy. There, they will uncover a secret connected to a decades-old political upheaval, a secret somebody is desperate to keep hidden -- though the price of that silence is unimaginable...
For your specific points: the back story (and this is spoilerific)
a supernova has happened relatively near to an inhabited human star; the shock wave is expanding at slightly less than light speed, and when it gets to the human planet, it's going to be game over. The previous human government covered it up - I think on the grounds of not being able to do anything to prevent it, so why let the people worry - and the secret is uncovered by Alex. In the end, an alien mind-reading species - with whom there's been off and on war in the past - send most of their navy to build a wall in space, just large enough to prevent the shockwave from hitting the planet; their efforts shame the humans into joining in and helping out.