How does nuclear fusion occur in stars?

Nuclear fusion in stars occurs when high temperatures and pressures cause atomic nuclei to collide and combine, releasing energy.

In more detail, stars, including our Sun, generate their energy through a process called nuclear fusion. This process takes place in the star's core, where the conditions of extreme temperature and pressure are met. The core temperature of a star like the Sun is around 15 million degrees Celsius, and the pressure is about 200 billion times Earth's atmospheric pressure at sea level.

The most common type of nuclear fusion in stars is the proton-proton chain reaction. This process begins with two hydrogen nuclei, or protons, colliding to form a heavier particle called a deuteron, which is a type of hydrogen nucleus consisting of one proton and one neutron. This reaction also releases a positron and a neutrino. The positron quickly annihilates with an electron, releasing energy in the form of gamma rays. The neutrino, a nearly massless particle that rarely interacts with matter, escapes from the star's core and travels into space.

The deuteron then collides with another proton to form a helium-3 nucleus, releasing a gamma ray photon. When two helium-3 nuclei collide, they form a helium-4 nucleus and two protons. This reaction also releases energy, primarily in the form of light and heat, which makes the star shine.

The energy produced by nuclear fusion not only makes the star shine but also keeps it from collapsing under its own gravity. The outward pressure of the energy produced by fusion balances the inward pull of gravity, keeping the star stable. This balance is known as hydrostatic equilibrium.

In summary, nuclear fusion in stars is a complex process that involves the collision and combination of atomic nuclei under extreme conditions, resulting in the release of energy that makes the star shine and maintains its stability.