The Astronomy textbook (which one do you have?) is basically right. I study white dwarfs, that are the end state for stars that are not massive enough to go supernova. So, obviously, the minimum supernova mass is the maximum white dwarf progenitor mass. One thing I have looked at is the question of how much of the original star's mass ends up in the white dwarf. The least massive white dwarfs are made by old G stars much like the sun, that have - no surprise - about one solar mass to start with. Only half of that matter ends up in the white dwarf, the rest is blown away near the end of the star's life as a regular starr (look up Planetary Nebulae, if you wish). If every star above 3 solar masses went supernova, we wouldn't have any white dwarfs above about 0.7 solar masses, but I've "weighed" scads of them that are more massive than that. The most massive white dwarfs end up with a bit more than a full solar mass. The stars that form the supermassive white dwarfs are among the best recyclers around - they start with around 8 solar masses, and get rid of nearly 7 before they turn into white dwarfs. We know this because we look at white dwarfs in star clusters, for which we know the ages because the stars above the "turnoff mass" have left the main sequence, and our stellar evolution models tell us how long it takes for a star of a given initial mass to evolve off the main sequence. When we look at the cluster white dwarfs, we "weigh" them and take their temperatures - sort of stellar geriatrics, if you will. We also have theoretical models that tell us how long it takes a white dwarf of a given mass to cool to a given temperature (they start off over 100,000 degrees K!). So, we know the age of the cluster (all the stars were formed essentially at once); subtracting the white dwarf cooling ages gives the main sequence lifetime of the progenitors. Since we know that lifetime as a function of initial mass, we then also know the initial mass of the stars that made the white dwarfs. Do that, and you have the initial-final mass relation for white dwarfs, that extends out to around 8 solar masses. A great new result, hot off the press, if you would like more detail than my little sketch provided, is publicly available as a pdf at http://arxiv.org/pdf/astro-ph/0409447 If you scroll all the way down to the bottom, the last figure pretty much tells the whole story. Good question! Best regards, David Finley

Note, someone changed the wording of this question after I posted it so that it is asking something completely different from what I originally asked. The question was about the cutoff line between the masses for stars that produce white dwarfs as opposed to those that produce neutron stars, not the difference in mass between a nova and supernova.