Perhaps a bit of revision on the matter of stellar nucleosynthesis is in order.
My theory is that when stars over about 125 SM have stranger nuclear reactions than previously believed. Blue-white giants are the star of choice for this example.
Let's presume the following reaction series:
2: 1/H\1.25 --- + 2UD (Pion) + e+/e- XX (10^-25 J Gamma) = 2/He\4.25
2e+ --- UD Reaction continues through the periodic table.
We have a way that hydrogen nuclei find electrons, shed positrons, reverse the polarity and charge of the positron under heavy gravitation (10^25G or higher). So far, we have developed a furious discharge of gamma, exciting nearby nuclei to break the strong force, allowing the creation of more pions, and developing greater heat.
Render the pions in 26/Fe\55 inert, and the formation of heavier nuclei becomes feasible, but not an absolute certainty, if the force of gravitation in the core is sufficient. Although heavier elements drain energy from the core of a star (possibly compact mass) the reacting lighter elements provide the needed energy to form heavier nuclei.
When the star reaches 55% 26/Fe\55, we will see a supernova, and the formation of a visible nebula. That is why the remaining 47 elements are much rarer than iron. However, know that stars have cores of compact mass before they can start nuclear fusion. The black holes that we believe form from stars, is the gravitational nightmare that dragged in all the mass in the first place, and when the fluff blows up, the black hole is still in business, often called a MaCHO (Massive Compact Halo Object). MaCHO's can be as small as singularities, and every bit as dense.
When the MaCHO drifts into another nebula, it will drag in that mass and start the process again, contrary to some popular theories. As much of that mass is heavier than helium and lithium, some strange physics begin to shape new elements that we cannot see because light cannot escape from them. When they reach a certain mass, they become supermassive black holes and attract whole galaxies. The stars we see follow the rules for black hole accretion disks perfectly.
Light elements dragged through singularities in a certain way fuse into heavier elements and careen through space as asteroids, comets, and nasty little micrometeroites that punch holes in our atmosphere at speeds you would find hard to believe.
In short, there is no one answer for the formation of heavy elements via stellar nucleosynthesis.
