Binary systems and their nuclear explosions

Abstract

The nuclear energy supply of a typical star like the Sun would be ∼ 1052 erg if all the hydrogen could be incinerated into iron peak elements. Since the gravitational binding energy is ∼ 1049 erg, it is evident that the nuclear energy content is more than enough to blow up the Sun. However, stars are stable thanks to the fact that their matter obeys the equation of state of a classical ideal gas that acts as a thermostat: if some energy is released as a consequence of a thermal fluctuation, the gas expands, the temperature drops and the instability is quenched. The first researchers to discuss the scenario under which stars could explosively release their nuclear energy were Hoyle and Fowler (1960). They showed that this could occur under conditions of dynamic compression, as a consequence of collapse, or under electron degeneracy. They also pointed out in their seminal paper that hydrogen could only be responsible for mild explosions, like novae, as a consequence of the necessity to convert two protons into two neutrons, and that only the thermonuclear fusion of carbon could be energetic enough to feed a strong explosion. They did not consider helium because by this epoch the He-burning mechanism was not yet known.