Skip to main content

Proton Fusion, the Sun's Power Source, Explained (Infographic)

Diagram of the proton-proton fusion reaction.
Stars are giant fusion reactors, smashing protons together to produce energy. (Image credit: by Karl Tate, Infographics Artist)

Inside stars like the sun, the extreme temperature rips atoms into their components: protons, neutrons and electrons. Under normal conditions, the mutual repulsion of individual protons ought to force them apart. Quantum-tunneling effects in the sun allow hot, high-speed protons to fuse into helium nuclei. This fusion reaction drives the sun’s radiance.

In the proton-proton fusion reaction, first two protons fuse. Usually the pair breaks apart again immediately, but once in a while one of the protons is transmuted into a neutron. The resulting proton-neutron pair is deuterium, a type of hydrogen. Also, a positron and a neutrino are emitted. When the positron encounters its antiparticle (an electron), the pair annihilates to form a gamma ray.

Then, another proton collides with the deuterium nucleus, forming a helium-3 nucleus (two protons and a neutron) plus a gamma ray. Gamma rays eventually work their way up from the core of the sun and out into space in the form of sunlight.

The helium-3 nucleus collides with another one, creating a helium-4 nucleus, plus two extra protons.

Solar Quiz: How Well Do You Know Our Sun?

The Sun in HD: Latest Photos by NASA's Solar Dynamics Observatory

Anatomy of Sun Storms & Solar Flares (Infographic)

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: community@space.com.

Karl Tate
Karl's association with SPACE.com goes back to 2000, when he was hired to produce interactive Flash graphics. Starting in 2010, Karl has been TechMediaNetwork's infographics specialist across all editorial properties.  Before joining SPACE.com, Karl spent 11 years at the New York headquarters of The Associated Press, creating  news graphics for use around the world in newspapers and on the web.  He has a degree in graphic design from Louisiana State University. To find out what his latest project is, you can follow Karl on Google+.