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Chapter 16: Problem 12

\(\mathbf{T} / \mathbf{F}:\) All stars on the main sequence are fusing hydrogen into helium in their cores.

Short Answer

Expert verified
True. All stars on the main sequence fuse hydrogen into helium in their cores.

Step by step solution

01

Understand the Main Sequence

The main sequence is a continuous band of stars that appears on plots of stellar color versus brightness. It represents a period in a star's life cycle where it is stable and fusing hydrogen into helium in its core.
02

Fusion Process in Main Sequence Stars

Stars on the main sequence generate their energy by fusing hydrogen atoms into helium atoms in their cores through nuclear fusion. This process releases a tremendous amount of energy and keeps the star stable.
03

Confirm the Statement

Since all stars on the main sequence are undergoing hydrogen fusion in their cores, the statement 'All stars on the main sequence are fusing hydrogen into helium in their cores' is true.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Stellar Lifecycle
Stars, like all things in the universe, go through a lifecycle. This life cycle starts from a molecular cloud and goes through various stages till it ends. A star's lifecycle is intimately connected to its mass. Larger stars evolve more quickly, whilst smaller stars have longer lifespans.
  • **Formation:** Stars begin in molecular clouds called nebulae, where dense regions collapse under gravity to form protostars.
  • **Main Sequence:** Once fusion starts in the core, the star enters the main sequence phase. Here, the star is stable and shines brightly by fusing hydrogen into helium.
  • **Red Giant or Supergiant Phase:** After hydrogen runs out in the core, the star expands and cools to form a red giant (if it's small to medium size) or a supergiant (if it's massive).
  • **Final Stages:** Depending on its mass, the star may go through stages like a supernova explosion, leading to remnants like white dwarfs, neutron stars, or black holes.
    Knowing these stages helps understand where and how stars generate energy, like during the main sequence with hydrogen fusion.
Hydrogen Fusion
Hydrogen fusion, also known as hydrogen burning, is the process that powers stars. During this process, hydrogen nuclei (protons) are combined under extreme pressures and temperatures to form helium.
In main sequence stars, hydrogen fusion occurs in the core, releasing an immense amount of energy. This energy radiates outward and provides the light and warmth we get from stars like our Sun.
The steps of hydrogen fusion in stars include:
  • **Proton-Proton Chain:** In smaller stars like the Sun, this is the primary method of hydrogen conversion. Protons collide and fuse to form helium-4, releasing energy in the process.
  • **CNO Cycle:** In more massive stars, the CNO cycle (carbon-nitrogen-oxygen cycle) plays a more significant role. It also converts hydrogen into helium but uses carbon, nitrogen, and oxygen as catalysts.
    Both hydrogen fusion methods are crucial in main sequence stars and explain their stability and energy output.
Nuclear Fusion
Nuclear fusion is the fundamental process at the heart of a star's energy production. It's what makes stars shine and allows them to stay in the main sequence phase.
Nuclear fusion involves combining lighter atomic nuclei to form a heavier nucleus. This fusion releases energy because the mass of the resulting nucleus is slightly smaller than the sum of its parts. The missing mass is converted into energy, according to Einstein’s equation: \(E=mc^2\).
Key points about nuclear fusion include:
  • **Conditions:** Fusion requires extremely high temperatures (millions of degrees) and pressures to overcome the repulsive forces between positively charged nuclei.
  • **Energy Source:** It's the primary source of energy for stars during their lifetime on the main sequence.
  • **Types:** While hydrogen fusion is the most common, stars also undergo other types of fusion as they evolve, like helium fusion in red giants.
  • **Fusion Reactors:** Understanding stellar fusion helps in developing potential future energy sources like fusion reactors on Earth.
    Understanding nuclear fusion provides insights into why stars are so bright and energetic, and how they produce the elements found throughout the universe.

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Most popular questions from this chapter

If a star follows a horizontal path across the H-R diagram, the star a. maintains the same temperature. b. stays the same color. c. maintains the same luminosity. d. keeps the same spectral type.

Do stars change their structure while on the main sequence? Why or why not?

The most massive stars have the shortest lifetimes because a. the temperature is higher in the core, so they burn their fuel faster. b. they have less fuel in the core. c. their fuel is located farther from the core. d. the temperatures are lower in the core, so they burn their fuel slower.

Degenerate matter is different from normal matter because as the mass goes up, a. the size goes down. b. the temperature goes down. c. the density goes down. d. the luminosity goes down.

When the Sun runs out of fuel in its core, the core will be a. empty. b. filled with hydrogen. c. filled with helium. d. filled with carbon.
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