Nuclear fusion and fission in stars and in cells

A key premise of my book, “The Sun Within,” is that cells derive energy from nuclear reactions similar to those in stars. 

In stars, the fusion of lighter elements into heavier elements provides energy. Fusion occurs under conditions of intense heat and pressure in a star’s core. There, electrons are stripped away from the atomic nuclei. This creates a plasma—a sea of electrons in which are found fully ionized, bare atomic nuclei. These nuclei have strong positive charges owing to their protons, and repel each other. Nonetheless, the high energy and pressure in the star’s core allows some nuclei to overcome their mutual repulsion and fuse.

In contrast, atoms within in a cell are not ionized, or only partly ionized. Some atoms have negative or positive charges owing to gains or losses of electrons, respectively. The attraction between a negatively charged atom and a positively charged atom could mean that nuclear fusion reactions occur more readily in cells than in stars. Enzyme movements in cells may direct two fusion candidate atoms towards each other, unlike the random motion in stars.

The Sun acquires energy from the fusion of four hydrogen nuclei to create helium nuclei. This fusion process occurs slowly, over the course of nearly ten billion years. Fusion reactions will terminate when most of the Sun’s hydrogen has been transformed into helium. In stars larger and hotter than the Sun, additional fusion reactions take place. Three helium nuclei can fuse to make carbon, carbon fuses with helium to make oxygen, two carbon nuclei fuse into magnesium, two oxygen nuclei fuse into sulphur, and so on. When these and many other fusion reactions occur, some of the mass of the protons and neutrons in the nucleus is converted to energy, according to Einstein’s formula, e = mc².

While fusion reactions predominate in stars, they are often coupled to fission reactions. For example, magnesium nuclei formed by carbon-carbon fusion seldom remain intact, but generally shed a helium nucleus to create neon. In the final step of the Sun’s conversion of hydrogen to helium, two helium-3 nuclei fuse while shedding two protons, yielding helium-4.

In a star eight or more times larger that the Sun, the final step of nuclear fusion creates iron and nickel. Their nuclei are extremely stable, with the highest binding energy of all the elements. Once they form, neither fusion nor fission reactions can yield any energy, so the star’s nuclear furnace shuts down. This removes the outward pressure that previously counteracted the star's immense gravity. An almost instantaneous gravitational collapse occurs, followed by a rebounding supernova explosion, leaving a remnant neutron star or a black hole.

In “The Sun Within,” I propose that living organisms use more of a balance between fusion and fission. Both can take place in various sites, such as the iron-sulphur reaction centres in mitochondria and chloroplasts. Through a process called “photodisintegration,” the gamma energy released through a fusion reaction splits a particle (such as a neutron) from the nucleus of another atom.

I suggest that solar energy may contribute additional energy to enable fission. In green plant chloroplasts, fission reactions could slightly predominate. This would help absorb excess solar energy on sunny days, and could even help cool the plant. In animal mitochondria, fusion reactions would slightly predominate, supplementing food energy and providing heat.

The theory of coupled, offsetting fusion and fission reactions can help explain how the immense forces within the atom can be used productively in living organisms, with net fission occurring in plants, and net fusion in animals.