A very energetic stellar explosion expending as much as 1044 joules and blowing off most of the star's mass, leaving a dense core (white dwarf, neutron star or black hole). The explosion fades in a year or two, although an expanding shell of gas speeds outward at about 10,000 to 20,000 km/sec, carrying about a fifth of the mass of the star (proportion varies).. Colliding with the interstellar medium the expanding shell can sweep up even more gas to become a supernova remnant
- Type Ia supernovae result from a white dwarf gaining mass from a close binary companion until it exceeds the Chandrasekhar limit. This results in stellar collapse, and the sudden fusion of degenerate fuels such as carbon trigger an explosion that destroys the star. A Type Ia supernova may have a luminosity of 4 billion Sol. It then declines rapidly and then more slowly.
- Type Ib supernovae are caused by the collapse the iron core of a massive star that has shed (or been stripped of) its outer envelope of hydrogen. The closely observed Regor Supernova which occured in 4120 AT was of this type.
- Type Ic supernovae are also caused by core collapse of a massive star, but in this case the star has lost much of its outer shell of helium. As they are formed from rare, very massive stars, the rate of Type Ib and Ic supernovae occurrence is much lower than the corresponding rate for Type II supernovae.
- Type II Supernovae result from the collapse of iron cores in massive stars, but in this case the star has retained most of its outermost shell of hydrogen and helium. Type Ib, Ic and the various Type II supernovae are collectively called core-collapse supernovae. A Type II supernova may have a luminosity of 0.6 billion Sol. It then declines in an irregular manner.
For these reasons artificial supernovae (such as those involved in the Gehenna event) can be detected far across the universe. Many instances of such artificial explosions have been observed in distant galaxies over the history of the Terragen Sphere, each one presumably associated with a highly advanced technological civilisation of some sort.
- Type III, IV, V, and VI supernovae do not occur in nature, they are caused by technological intervention, such as the use of conversion weapons. The Gehenna Cluster is the result of 50 Type V supernovae, evidently triggered by the rogue archailect Verifex. These stellar explosions have a significantly different optical signature from naturally occurring supernovae; the star is almost certainly smaller than a natural supernova candidate, but the amount of energy produced by the explosion is dependent on the technology used rather than on the mass of the star. Most artificial supernovae are not surrounded by shells of previously expelled gases.
Conversely the vast amount of energy put out by a supernova progenitor star can allow an advanced civilisation to use that energy in an effort to delay the collapse of the core, usually by lifting matter from the surface layers. In this way a supernova progenitor star may be stabilised for an indefinite period. Some distant galaxies show lower than expected rates of supernova formation- one possible reason for this is the existence of an advanced civilisation in that galaxy which has used technology to reduce the number of exploding stars.