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Chapter 15: Problem 10

The Hayashi track is a nearly vertical evolutionary track on the H-R diagram for low-mass protostars. Which of the following would you expect from a protostar moving along a vertical track? a. The star remains the same brightness. b. The star remains the same luminosity. c. The star remains the same color. d. The star remains the same size.

Short Answer

Expert verified
b. The star remains the same luminosity.

Step by step solution

01

Understanding the Hayashi Track

The Hayashi track describes the early evolutionary stages of low-mass protostars on the Hertzsprung-Russell (H-R) diagram. Along this track, protostars primarily change their temperature while their luminosity remains relatively constant.
02

Analyzing Vertical Movement

Movement along a vertical track on the H-R diagram suggests changes in temperature. Since luminosity is a function of both temperature and size, and it remains constant, either temperature or size would have to change.
03

Evaluate Each Option

a. Incorrect: Brightness changes as temperature changes. b. Correct: Luminosity remains the same on a vertical path. c. Incorrect: Color changes as temperature changes. d. Incorrect: Size changes to maintain constant luminosity while temperature changes.

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Key Concepts

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

H-R diagram
The Hertzsprung-Russell (H-R) diagram is a fundamental tool in astrophysics used to plot stars according to their luminosity and temperature. This scatter plot shows the relationship between these two properties and helps understand a star's evolutionary stage. The vertical axis represents luminosity or brightness, often in terms of the Sun's brightness, while the horizontal axis charts temperature, with hotter stars on the left and cooler stars on the right. The diagram features several key regions, including the main sequence, where stars spend most of their lifetimes, and the red giant branch and white dwarf region, illustrating different phases of stellar evolution.
protostars
A protostar is an early stage in stellar evolution. It's formed from a collapsing cloud of gas and dust in space. Protostars are still gathering mass from their surroundings and have not yet started nuclear fusion in their cores. On the H-R diagram, protostars generally occupy the region above the main sequence because they are very luminous, despite their relatively low temperatures. As they approach the main sequence, their temperatures increase while maintaining a nearly constant luminosity, following the path known as the Hayashi track.
stellar evolution
Stellar evolution refers to the series of phases that a star undergoes over its lifetime. This process depends largely on the star's initial mass.
  • *In the beginning*, a star forms from a protostar as nuclear fusion ignites.
  • *Next, it enters the main sequence*, where it spends most of its life fusing hydrogen into helium.
  • *Post-main sequence*, stars may become red giants or supergiants, burning heavier elements in their cores.
  • *Finally*, depending on the mass, a star might end its life as a white dwarf, neutron star, or black hole.
luminosity
Luminosity measures how much energy a star emits per unit time. It's intrinsic to the star and independent of its distance from Earth.
  • On the H-R diagram, stars with higher luminosity are plotted higher up.
  • Luminosity is directly related to the star's size and temperature; larger or hotter stars are more luminous.
  • For instance, on the Hayashi track, protostars maintain a nearly constant luminosity as they contract and heat up before reaching the main sequence.
temperature changes
Temperature changes are an essential part of a star's evolution. They reflect a star's surface temperature and color.
  • For example, as a protostar travels along the Hayashi track on the H-R diagram, its temperature increases while its luminosity stays roughly the same.
  • This change in temperature affects the star's color, with hotter stars appearing blue and cooler stars appearing red.
  • These changes also influence other properties like the star's size and the type of nuclear reactions occurring in its core.

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Most popular questions from this chapter

How does the material in interstellar clouds and intercloud gas differ in density and distribution?

The Stratospheric Observatory for Infrared Astronomy (SOFIA) is a 2.5 -meter telescope on a modified Boeing 747 aircraft. Go to the SOFIA website (http://sofia.usra.edu). Why have astronomers put an infrared telescope on an airplane? What has been detected with this telescope?

Phases of the interstellar medium include (choose all that apply a. hot, low-density gas. b. cold, high-density gas. c. hot, high-density gas. d. cold, low-density gas.

The interstellar medium is approximately 99 percent gas and percent dust. Why does dust and not gas block a visible-light view of the galactic center?

Interstellar gas atoms typically cool by colliding with other gas atoms or grains of dust; during the collision, each gas atom loses energy and hence its temperature is lowered. How does this explain why very low-density gases are generally so hot, while dense gases tend to be so cold?
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