The Verubin Nebula was a nebula that contained intense radiation and unstable electromagnetic fields, as well as a dilithium nursery, at least one neutron star, and the planet Theta Zeta. The nebula was accessible via a transwarp conduit, although doing so was extremely treacherous.
In 3064, the KSF Khi'eth crashed on Theta Zeta while charting its dilithium nursery. Five years later, Theta Zeta was ground zero for the Burn, which caused all refined dilithium to become inert and consequently destroyed most of the galaxy's starships.
By 3189, the Khi'eth's automated distress signal was still actively broadcasting, but had been distorted by magnetic interference to form the melody, "music" that became commonly known across the galaxy. In that year, members of the USS Discovery crew were able to track the source of the Burn to the Verubin Nebula, and eventually found the Khi'eth and its sole survivor, Su'Kal. Some time after that, the United Federation of Planets began mining dilithium from Theta Zeta and the nebula. (DIS: "The Sanctuary", "Terra Firma, Part 1", "Terra Firma, Part 2", "Su'Kal", "That Hope Is You, Part 2")