The Veil Nebula, part of the Cygnus Loop supernova remnant
The Cygnus Loop is a supernova remnant in the constellation Cygnus, about 1470 light years from Sol. The supernova exploded about 16,600 years ago (approximately 6000 BT) and is still expanding, forming a cloud of gas. The nebula is almost spherical, with some bright filaments. The region has long been colonized by a number of exotic clades.
Supernova Remnant - Text by M. Alan Kazlev The expanding and cooling shell of gas and dust that is visible for thousands of years after a supernova. After a few tens of thousands of years supernova remnants mix with the interstellar medium and dissipate.