/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 6 What are thermal pulses in AGB s... [FREE SOLUTION] | 91影视

91影视

Log out

Learning Materials

Features

Discover

Chapter 20: Problem 6

What are thermal pulses in AGB stars? What causes them? What effect do they have on the luminosity of the star?

Short Answer

Expert verified
Thermal pulses in AGB stars are periodic instabilities in the helium-burning shell caused by helium shell flash, producing an explosive release of energy that temporarily increases the star's luminosity. The cycle repeats as the conditions in the shell reset after each pulse, causing the variable luminosity commonly observed in AGB stars.

Step by step solution

01

Understanding Thermal Pulses in AGB Stars

Thermal pulses are periodic instabilities that occur within the shell surrounding the core of an Asymptotic Giant Branch (AGB) star. They are episodes of nuclear fusion that occur in the helium-burning shell. This process functions on a cyclical basis where the helium in the shell contracts and heats up, leading to increased rates of nuclear fusion and releasing a large amount of energy as the helium is converted into carbon. This outpouring of energy, or 'pulse', causes the star to expand and the shell to cool, slowing down the rate of fusion and ultimately resting until the next pulse.
02

Identifying Causes of Thermal Pulses

These thermal pulses are caused by a process known as helium shell flash or helium flash. This occurs when the helium in the shell of an AGB star contracts and heats up, increasing the rate of nuclear fusion. This causes an unstable and explosive release of energy, which results in a thermal pulse. The main catalyst for this process is the decreasing density and temperature of the helium shell outside the inert carbon-oxygen core, driving the necessary conditions for a helium shell flash and a subsequent thermal pulse.
03

Influence of Thermal Pulses on Star Luminosity

Thermal pulses have significant effects on the luminosity of an AGB star. After a thermal pulse occurs, it causes the star to expand significantly and increases its brightness or luminosity. This increase is temporary, and once the energy pulse is over, the star will contract and its luminosity will decrease until the conditions are ripe for another thermal pulse. This cyclical nature of thermal pulses gives an AGB star its characteristic pulsating or variable luminosity.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with 91影视!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

What is nuclear density? Why is it significant when a star's core reaches this density?

How do supernova remnants produce radiation at nonvisible wavelengths?

. Use a telescope to observe the remarkable triple star 40 Eridani, whose coordinates are R.A. \(=4^{\mathrm{h}} 15.3^{\mathrm{m}}\) and Decl. \(=-7^{\circ} 39^{\prime}\). The primary, a 4.4-magnitude yellowish star like the Sun, has a 9.6-magnitude white dwarf companion, the most easily seen white dwarf in the sky. On a clear, dark night with a moderately large telescope, you should also see that the white dwarf has an 11 th-magnitude companion, which completes this most interesting trio.

Consider a high-mass star just prior to a supernova explosion, with a core of diameter \(20 \mathrm{~km}\) and density \(4 \times 10^{17}\) \(\mathrm{kg} / \mathrm{m}^{3}\). (a) Calculate the mass of the core. Give your answer in kilograms and in solar masses. (b) Calculate the force of gravity on a 1-kg object at the surface of the core. How many times larger is this than the gravitational force on such an object at the surface of the Earth, which is about 10 newtons? (c) Calculate the escape speed from the surface of the star's core. Give your answer in \(\mathrm{m} / \mathrm{s}\) and as a fraction of the speed of light. What does this tell you about how powerful a supernova explosion must be in order to blow material away from the star's core?

Why does the mass of a star play such an important role in determining the star's evolution?
See all solutions

Recommended explanations on Physics Textbooks

Rotational Dynamics

Read Explanation

Dynamics

Read Explanation

Physics of Motion

Read Explanation

Engineering Physics

Read Explanation

Wave Optics

Read Explanation

Solid State Physics

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.