I am looking for a story that opens with a terrorist organization that destroys the only wormhole connecting a planetary system to the rest of the galaxy.
The story occurs centuries after humanity has contacted other civilizations in the galaxy and been accepted into the galactic community. Most inhabited planetary systems are connected to other planetary systems by one or more wormholes. The wormholes are large enough to allow spaceships to pass through.
The story opens in a distant star system with a few colonized worlds. The worlds are inhabited by humans and various alien species. A terrorist organization accelerates a city-sized rock from deep space up to near light speed. The rock's kinetic energy is about the same mass-energy equivalence as a gas giant planet. The rock impacts the only wormhole in the system and destroys it in a huge explosion.
The survivors are left completely isolated from the rest of the galaxy. One day they could send emails to their families or take a trip through the wormhole to the next nearest inhabited star system. The next day, they are alone.
They get a radio message after a few dozen years from a nearby star system. The message says another wormhole has been created for them and is being delivered now. Delivery will take over two centuries. This means they will never see their families again. They will never leave that planetary system for the rest of their lives.