The Big Crush was an event that happened in 1 ABY and resulted in the destruction of one of the planets in the Taspan system. It was caused by an accident with the gravity well projector technology the Galactic Empire was developing there. At the time of the Battle of Mindor the remains of the planet had not yet settled into stable orbits, making travel in the system extremely dangerous. As computed by one of Luke Skywalker's analysts, his task force would have lost two ships after only an hour in the system just from asteroid impacts.
The Big Crush was temporarily of great benefit to the Melters living in Taspan II's crust, scattering them and letting them absorb and feed on stellar radiation more easily. Luke, in communion with them, understood this to have been a brief golden age.