Originally posted by sonhouse
So a type I is a regular nova and a type II is a supernova? How much energy difference are we talking about? Thousand times? Million times?
No, the classification of supernovas depends on the spectrum of light emitted. Type II supernovas show hydrogen absorption lines, type I supernovas do not. Type I supernovas are divided into Type Ia and types Ib and Ic, type Ia has a absorption line for silicon. Type Ib and Ic do not, Ib has helium absorption lines and Ic does not. They classify them like this because it depends on observations - which won´t change - not on theories as to why stars do this which might.
Type II supernovas are believed to happen due to core collapse of stars > 3 solar masses. Type Ib and Ic supernovas happen due to core collapse in a star which has lost some of its outer layers, which explains the absence of hydrogen and in Ic supernovas helium lines.
Type Ia supernovas are believed to be caused by a white dwarf star accreting material from a giant binary partner which causes it to gain mass until it reaches the Chandrasakar limit which means it collapses, the collapse causes it to undergo a fusion burn of carbon of a large fraction of the material in the star in a few seconds. The reaction is enough to completely destroy the star.
A nova is a white dwarf star which is not (necessarily) close to the Chandresakar limit which is accreting hydrogen. As the hydrogen builds up on the surface of the star it is occasionally explosively burned in a fusion reaction to helium. This is a hydrogen flash and different from a supernova event which is far more energetic. The star survives the hydrogen flash more or less intact and after accreting more material may supernova in the future.
The star in the science fiction novel cannot supernova as it is too young, and there is no known mechanism for a star in it´s stage of life and of its size to nova. The aliens would have to have some method to either compress the core or make it overheat. This is more like a type II supernova than a nova.