The “End of the world” -chronicle hexalogy is all about the disaster. Really long story short, Seyllin I is a planet destroyed in the Isogen-5 event, just one of many but gave it a face since it had something like a few billion people living in it.
The Isogen-5 event is then the simultaneous destruction of carefully positioned quantum entangled stockpiles of Isogen-5 around New Eden cluster that caused stars of specific spectrum (O1) to go nova in the Eve cluster and beyond. This was planned and done millennia ago in the early days of colonization, as only ancient terrans knew how to produce/capture and store the Isogen-5 material en masse.
This in turn was a feat of stellar engineering by an unknown ancient terran faction - Talocan are at the time heavily assumed to be the culprits but not certain - that caused the appearance of the artificial wormholes in New Eden by manipulating the very fabric of space-time.