Question

The universe cooled after the Big Bang. At some point, hydrogen atoms combined to form helium. What is this process called?

Answer 1

In the basic Hydrogen fusion cycle, four Hydrogen nuclei (protons) come together to make a Helium nucleus. This is the simple version of the story. There are actually electrons, neutrinos and photons involved that make the fusion of Hydrogen into Helium possible.

Answer 2

This process is called as Nuclear Fusion