The Galatea was one of humanity's first orbital space stations. Its mission was unknown, but it carried some radioactive materials on board.
Individual research has shown, however, that the pattern of radiation dispersal does not match with the appearance of novas.
In truth, the explosion of the Galatea was likely caused by the dramatic and messy eruption of one of the first novas, who happened to be one of the astronauts on board. It also provided a useful "scapegoat" for the nova phenomenon.
The beginning of the Nova Age was more than likely caused by Divis Mal. He was able to replicate the Hammersmith Incident, except focused purely in the quantum part of the spectrum. The resultant flood of quantum energies was likely upkept either by Mal or by one of his associates.