Fusion on the Sun

Source: NASA Goddard Space Flight Center, CC BY 2.0, via Wikimedia Commons

At temperatures of 15 million degrees Celcius in the Sun’s core, hydrogen gas becomes plasma, the fourth state of matter. In a plasma, the negatively charged electrons in atoms are completely separated from the positively charged atomic nuclei (or ions). The Sun’s gravitational force confines the positively-charged hydrogen nuclei and the high temperatures cause the nuclei to move around furiously. As a result they collide at high speeds overcoming the natural electrostatic repulsion that exists between the positive charges and subsequently fuse to form the heavier helium.

From hydrogen to helium in three steps

  • In the first stage two protons combine and one of them converts into a neutron to form a nucleus of the heavy isotope of hydrogen known as deuterium.
  • Next, the deuterium nucleus combines with another proton to form the light helium isotope known as helium-3.
  • Finally, two helium-3 nuclei combine to form helium-4, releasing two protons.

Energy release

Overall, four protons are converted into one helium nucleus. Energy is released because the helium nucleus has slightly less mass than the original four protons. The total amount of energy released for each conversion of four hydrogen nuclei into a helium nucleus is about 10 million times more than is produced by the chemical reaction when hydrogen combines with oxygen to form water.

Proton-proton chain reaction

The proton-proton chain reaction is one of the processes by which stars fuse hydrogen into helium. By Doctor C (Own work) [CC BY-SA 4.0, via Wikimedia Commons

Did you know...

In its core, the Sun fuses 620 million metric tons of hydrogen each second.