Galaxy-crackers, also known as vacuum energisers, were the pinnacle of Starbuilder weaponry. They worked by causing a reverse false vacuum collapse, heightening the energy of a part of existence and letting it implode upon a target, annihalating it.
Galaxy-crackers, as their name suggests, are perfectly capable of destroying entire galaxies. By using wormholes and sensors, an emitter could triangulate the position of the target with perfect accuracy. Once this was done, they would heighten the energy of the existence on the intended target, destroying it instantly and turning it into energy once the bubble imploded. This methood has no chance of destroying a universe, unlike vacuum destabilisers, which lower the energy of part of existence to destroy an entire universe unless stopped. The only known defence is to be surrounded by an existential stabiliser field, which prevents the laws of physics from being rewritten in that area.