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Chapter 17: Problem 11

T/F: The end result of the CNO cycle is that four hydrogen nuclei become one helium nucleus.

Short Answer

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Step by step solution

01

Understand the CNO Cycle

The Carbon-Nitrogen-Oxygen (CNO) cycle is one of the processes by which stars convert hydrogen into helium.
02

Breakdown the Process

During the CNO cycle, protons (hydrogen nuclei) are used to convert carbon into nitrogen and then into oxygen, ultimately leading to the formation of a helium nucleus. The cycle uses four hydrogen nuclei in its steps.
03

Verify the Outcome

Check if the end product of the CNO cycle is a helium nucleus or something else. The end result indeed synthesizes a helium-4 nucleus from four hydrogen nuclei.
04

Confirm the Statement

Based on the breakdown, confirm that the statement 'The end result of the CNO cycle is that four hydrogen nuclei become one helium nucleus' is true.

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Key Concepts

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

Stellar Nucleosynthesis
Stellar nucleosynthesis is the process by which elements are formed within stars. It involves nuclear reactions that create new atomic nuclei from pre-existing nucleons (protons and neutrons). This incredible process happens under extreme temperatures and pressures found in the cores of stars.

There are multiple stages and types of stellar nucleosynthesis:
  • Hydrogen fusion (or hydrogen burning): This is the primary phase where hydrogen nuclei combine to form helium.
  • Helium fusion: Once a star has exhausted much of its hydrogen, it starts fusing helium into heavier elements like carbon and oxygen.
  • Advanced fusion stages: In very massive stars, elements heavier than carbon are formed, such as iron.
Each stage of nucleosynthesis releases energy, which provides the radiation pressure necessary to keep the star from collapsing under its own gravity. Without these nuclear fusion processes, stars would not shine.
Hydrogen to Helium Conversion
Hydrogen to helium conversion is the foundational nuclear reaction in stars. In the cores of stars like the Sun, this conversion occurs primarily through two mechanisms: the proton-proton (pp) chain reaction and the carbon-nitrogen-oxygen (CNO) cycle.

The CNO cycle is more dominant in stars that are heavier and hotter than the Sun, while the pp chain is more critical in smaller stars.
  • Proton-Proton Chain: In this process, hydrogen nuclei (protons) combine to form deuterium, which then forms helium-3, and finally helium-4.
  • CNO Cycle: This mechanism involves hydrogen nuclei interacting with existing carbon, nitrogen, and oxygen nuclei to ultimately produce helium.
Both of these processes produce not just helium, but also energy in the form of photons. This energy travels from the core of the star to its surface and gets emitted as light.
Carbon-Nitrogen-Oxygen Process
The carbon-nitrogen-oxygen (CNO) process, or cycle, is a series of nuclear reactions that help convert hydrogen into helium in stars. This cycle is especially significant in stars heavier and hotter than the Sun.
The steps in the CNO cycle are as follows:
  • Carbon-12: A carbon-12 nucleus captures a proton (hydrogen nucleus) to form nitrogen-13.
  • Nitrogen-13: This nucleus decays into carbon-13 by emitting a positron (a process that releases energy).
  • Carbon-13: This takes in another proton, forming nitrogen-14.
  • Nitrogen-14: Once again, a proton is captured, leading to oxygen-15.
  • Oxygen-15: This decays into nitrogen-15 by emitting a positron.
  • Nitrogen-15: Finally, it captures a proton and splits into a helium-4 nucleus and carbon-12, which can start the cycle again.
In this way, the CNO cycle continuously converts hydrogen to helium, with carbon, nitrogen, and oxygen nuclei acting as catalysts. The net result, as stated, is that four hydrogen nuclei become one helium nucleus.

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Most popular questions from this chapter

In a high-mass star, hydrogen fusion occurs via a. the proton-proton chain. b. the CNO cycle. c. gravitational collapse. d. spin-spin interaction.

Iron fusion cannot support a star, because a. iron oxidizes too quickly b. iron absorbs energy when it fuses. c. iron emits energy when it fuses. d. iron is not dense enough to hold up the layers.

Recordings show that SN 1987A was detected by neutrinos on February \(23,1987 .\) About 3 hours later it was detected in optical light. What was the reason for the time delay?

T/F: A supernova can be as bright as its entire host galaxy.

The approximate relationship between the luminosity and the period of Cepheid variables is \(L_{\text {star }}\) \(\left(\operatorname{in} L_{\odot}\right)\) \(=335 P\) (in days). Delta Cephei has a cycle period of 5.4 days and a parallax of 0.0033 arcsecond (arcsec). A more distant Cepheid variable appears \(1 / 1,000\) as bright as Delta Cephei and has a period of 54 days. a. How far away (in parsecs) is the more distant Cepheid variable? b. Could the distance of the more distant Cepheid variable be measured by parallax? Explain.
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