Question

How will this circle graph change as the Sun ages? A. The hydrogen slice will get smaller. B. The hydrogen slice will get larger. C. The helium slice will get smaller. D. The circle graph will not change.

Short answer

A. The hydrogen slice will get smaller.

Step-by-step solution

Understanding the Composition of the Sun

Initially, the Sun is primarily composed of hydrogen, which fuses to form helium through nuclear fusion in its core. This composition is reflected in the circle graph where the hydrogen slice is the largest.

Considering the Aging Process of the Sun

As the Sun ages, it continuously converts hydrogen into helium. This process reduces the amount of hydrogen in its core and increases the amount of helium.

Predicting Changes in the Circle Graph

Given that hydrogen is decreasing while helium is increasing, the hydrogen slice on the graph will diminish over time, while the helium slice will proportionally increase.

Evaluating the Options

The changes as described align with option A, where the hydrogen slice will get smaller. B is incorrect because hydrogen is decreasing, and C is incorrect because helium is increasing. D is invalid since the composition changes, represented by the graph, occur over time.

Key concepts

Nuclear Fusion

Nuclear fusion is a powerful process that fuels our Sun and many other stars in the universe. In the Sun’s core, extreme pressures and temperatures force hydrogen atoms to smash together. This process helps them to overcome their natural repulsion towards each other. When two hydrogen nuclei combine, they form a single helium nucleus. This fusion releases a tremendous amount of energy, which not only provides the Sun with its power but also creates the light and warmth that reaches Earth.
The key stages involved in nuclear fusion for stars like our Sun are:

• Hydrogen nuclei, called protons, move at high speeds due to the extremely hot temperatures.
• These protons collide with enough force to overcome the electrostatic forces that normally keep them apart.
• Fusion reactions convert hydrogen into helium, releasing energy in the form of light and heat.

Fusion is pivotal for the Sun's stability, maintaining its balance between the explosive energy radiating outwards and the gravitational forces pulling inwards.

Stellar Life Cycle

The stellar life cycle describes the various stages a star undergoes from its formation to its demise. Our Sun is currently in the "main sequence" stage of its life—a long period of stability where hydrogen fuses into helium in the core. However, like all stars, the Sun will eventually run low on fuel and alter its state.
Let's break down the main stages in a stellar life cycle:

• Birth: Stars begin as clouds of dust and gas, which collapse under gravity to form protostars.
• Main Sequence: Stars, like the Sun, spend most of their lives fusing hydrogen to helium in a stable balance.
• Red Giant: Once hydrogen depletes, the star expands and cools as it fuses helium and other heavier elements.
• Death: Depending on the star's mass, it can become a white dwarf, neutron star, or even a black hole.

This cycle dictates the transformation stars undergo, affecting their composition and structure over millions or billions of years.

Hydrogen to Helium Conversion

In the Sun, the conversion of hydrogen into helium is a fundamental process. This transformation occurs during nuclear fusion in the Sun's core and is essential for producing the energy that supports all solar activity. Over time, this conversion process gradually shifts the Sun’s composition.
Here’s how the transformation of hydrogen to helium affects the Sun:

• At the onset, the Sun consists majorly of hydrogen, constituting about 75% of its mass.
• As nuclear fusion progresses, helium accumulates in the core as a byproduct of fusing hydrogen atoms.
• This gradual conversion means the Sun’s core gets denser and hotter, causing changes in its life cycle and activities.
• Over billions of years, the hydrogen present diminishes, resulting in increased helium proportions in the star.

Understanding this conversion reveals why, as stated in the exercise, the hydrogen slice on the circle graph will get smaller while the helium slice will grow.