Question

What forms when the Sun fuses hydrogen? A) carbon C) iron B) oxygen D) helium

Short answer

Helium forms when hydrogen is fused in the Sun.

Step-by-step solution

Understanding Nuclear Fusion

In stars like the Sun, the process of nuclear fusion occurs in the core. This is where lighter elements are fused together to form heavier elements, releasing energy.

Identifying the Fusion Process in the Sun

The Sun primarily fuses hydrogen nuclei (protons) into helium nuclei through a series of reactions known as the proton-proton chain reaction. This is the primary fusion process in the Sun due to its relatively low mass compared to more massive stars.

Matching to the Provided Options

Given the choices, we need to identify which element results from the fusion of hydrogen in the Sun. We know from the fusion process that hydrogen fuses to form helium. Thus, option D) helium is the correct answer.

Key concepts

Proton-Proton Chain Reaction

The proton-proton chain reaction is the fundamental process that fuels the Sun and other similar-sized stars. This series of nuclear reactions begins when two hydrogen nuclei (protons) collide at extremely high temperatures and pressures in the stellar core.
The resulting chain of reactions ultimately converts hydrogen into helium, releasing a tremendous amount of energy in the process.

• First step: Two protons fuse to create a deuterium nucleus, which is one proton and one neutron. This step also releases a positron and a neutrino.
• Second step: Another proton then collides with the deuterium nucleus, forming a helium-3 nucleus (two protons and one neutron) and releasing a gamma-ray photon.
• Final step: Two helium-3 nuclei collide, producing a helium-4 nucleus and two protons. These protons are freed to start the cycle again.

This reaction is essential because it balances the gravitational forces pulling matter into the star with the energy produced that pushes outward, effectively maintaining the Sun’s stability over billions of years.

Stellar Nucleosynthesis

Stellar nucleosynthesis refers to the processes by which elements are formed within the stars. This phenomenon occurs in the stellar cores under extreme conditions of temperature and pressure. For stars like the Sun, the most significant form of nucleosynthesis is the fusion of hydrogen into helium via the proton-proton chain reaction. However, nucleosynthesis in more massive stars involves the fusion of heavier elements.
Understanding the sequence of nucleosynthesis provides insights into how stars evolve over their lifetimes and how they contribute to forming elements in the universe. As stars run out of hydrogen fuel, they may begin to fuse helium and create even heavier elements. This cyclic process enriches the cosmos, eventually leading to the diverse array of elements found throughout the universe.

Hydrogen Fusion

Hydrogen fusion is the basic mechanism that powers stars and the fundamental step in the entire life cycle of stars. In the Sun and similar stars, hydrogen fusion occurs as protons, primarily hydrogen nuclei, merge to form helium. This fusion process requires immense heat and pressure found in the core of stars. As hydrogen atoms combine, they release energy in the form of light and heat. This energy is what we observe as sunlight.
The efficiency and duration of hydrogen fusion are what determine the stages of a star's life. In stars like the Sun, hydrogen fusion can sustain the stellar structure and energy output for billions of years, eventually transforming the core's composition and enabling further fusion processes as the star ages.

Helium Production

Helium production is a direct outcome of the nuclear fusion processes in stars, primarily initiated through the hydrogen fusion in the Sun via the proton-proton chain reaction. As pairs of hydrogen nuclei fuse, the end product is helium, which accumulates in the star’s core over time. This build-up of helium is a critical factor in a star's lifecycle because, over time, the ratio of hydrogen to helium affects the star’s energy production and structural changes.
In stars more massive than the Sun, and under different fusion cycles, helium itself serves as the starting material for even heavier element production. The synthesis of helium through hydrogen fusion effectively fuels the brilliance and longevity of stars, fundamentally shaping their evolutionary paths.

• Helium results from fusing four protons in the core.
• The process helps balance the forces within the star, preventing collapse and steadying the star over long periods.