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Mobile App Chapter 16: Problem 4
Place the following steps in the evolution of a low-mass star in order a. main-sequence star b. planetary nebula ejection c. horizontal branch d. helium flash e. red giant branch f. asymptotic giant branch g. white dwarf
Short Answer
Expert verified
a, e, d, c, f, b, g
Step by step solution
01
- Main-Sequence Star
A low-mass star spends the majority of its life in the main-sequence phase, where it fuses hydrogen into helium in its core.
02
- Red Giant Branch
After exhausting the hydrogen in its core, the star expands and cools to become a red giant. In this phase, hydrogen fusion occurs in a shell surrounding the core.
03
- Helium Flash
The core contracts and heats up until it reaches a temperature sufficient for helium fusion to begin explosively in an event known as the helium flash.
04
- Horizontal Branch
Following the helium flash, the star stabilizes and burns helium in its core while maintaining hydrogen shell burning. The star is now on the horizontal branch.
05
- Asymptotic Giant Branch
Once the helium in the core is exhausted, the star moves to the asymptotic giant branch, where it has a carbon-oxygen core and burns helium and hydrogen in shells around the core.
06
- Planetary Nebula Ejection
The outer layers of the star are ejected, forming a planetary nebula. The core left behind continues to contract.
07
- White Dwarf
The remaining core becomes a white dwarf, which will slowly cool and fade over time.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Main-Sequence Star
The life of a low-mass star begins with the main-sequence phase. During this phase, the star fuses hydrogen into helium in its core. This is the longest stage in a star's life, lasting for billions of years.
The process of hydrogen fusion releases vast amounts of energy, which counteracts the gravitational force trying to compress the star.
This energy makes the star shine brightly. Throughout its time on the main sequence, the star remains relatively stable and maintains a constant size and brightness.
The process of hydrogen fusion releases vast amounts of energy, which counteracts the gravitational force trying to compress the star.
This energy makes the star shine brightly. Throughout its time on the main sequence, the star remains relatively stable and maintains a constant size and brightness.
Red Giant Branch
After a low-mass star exhausts the hydrogen in its core, it transitions to the red giant branch. During this phase, the core contracts and heats up, but hydrogen fusion continues in a shell surrounding the core. This causes the outer layers of the star to expand and cool, giving the star a reddish appearance.
As a red giant, the star becomes far larger in size compared to its main-sequence state, and its luminosity increases significantly. This phase is relatively short-lived compared to the main-sequence phase.
As a red giant, the star becomes far larger in size compared to its main-sequence state, and its luminosity increases significantly. This phase is relatively short-lived compared to the main-sequence phase.
Helium Flash
The next major event in the evolution of a low-mass star is the helium flash. During this stage, the core temperature becomes high enough to ignite helium fusion in a sudden and explosive manner. This occurs because the core is so dense that the onset of helium fusion is extremely rapid.
The helium flash leads to the core expanding and stabilizing somewhat, reducing the pressure in the outer layers and allowing the star to shed some of its outer material. This phase is brief but critical in the star's evolution.
The helium flash leads to the core expanding and stabilizing somewhat, reducing the pressure in the outer layers and allowing the star to shed some of its outer material. This phase is brief but critical in the star's evolution.
Horizontal Branch
Following the helium flash, the star enters the horizontal branch phase. In this phase, the star stabilizes and burns helium in its core while hydrogen continues to burn in a shell surrounding the core. This balanced burning allows the star to maintain a relatively stable size and temperature for a while.
The star's position on the horizontal branch reflects this stability and is significant in the Hertzsprung-Russell diagram, which astronomers use to plot stars according to their luminosity and temperature.
The star's position on the horizontal branch reflects this stability and is significant in the Hertzsprung-Russell diagram, which astronomers use to plot stars according to their luminosity and temperature.
Asymptotic Giant Branch
After the horizontal branch phase, the star moves to the asymptotic giant branch. Here, the star has a core composed of carbon and oxygen, resulting from earlier fusion processes.
In this phase, the star burns helium and hydrogen in concentric shells surrounding the core. The star once again swells to enormous sizes and becomes highly luminous.
The asymptotic giant branch is another phase of significant expansion and instability, leading to mass loss from the outer layers of the star.
In this phase, the star burns helium and hydrogen in concentric shells surrounding the core. The star once again swells to enormous sizes and becomes highly luminous.
The asymptotic giant branch is another phase of significant expansion and instability, leading to mass loss from the outer layers of the star.
Planetary Nebula Ejection
As the star continues to evolve, its outer layers are eventually ejected into space, forming what is known as a planetary nebula. This ejection process is driven by the intense radiation and stellar winds emitted from the core.
The planetary nebula is a beautiful and complex structure of ionized gas that can be observed with telescopes. It represents the outer layers of the star spread over a vast area, while the core becomes exposed and continues to shrink.
The planetary nebula is a beautiful and complex structure of ionized gas that can be observed with telescopes. It represents the outer layers of the star spread over a vast area, while the core becomes exposed and continues to shrink.
White Dwarf
The final stage in the life of a low-mass star is becoming a white dwarf. After the ejection of the planetary nebula, the leftover core of the star, now stripped of its outer layers, becomes a white dwarf.
A white dwarf is incredibly dense and composed primarily of carbon and oxygen. It no longer undergoes fusion and will slowly cool and fade over time.
Despite its small size, the white dwarf remains extremely hot and radiates residual heat for billions of years before it finally grows cold and dark.
A white dwarf is incredibly dense and composed primarily of carbon and oxygen. It no longer undergoes fusion and will slowly cool and fade over time.
Despite its small size, the white dwarf remains extremely hot and radiates residual heat for billions of years before it finally grows cold and dark.
