Log out Go to App
Go to App

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.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!

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

The red supergiant Betelgeuse in the constellation Orion will explode as a supernova at some time in the future. Use the Stamy Night Entbusiast \({ }^{\mathrm{TM}}\) program to investigate how the supernova might appear if this explosion were to happen tonight. Click the Home button in the toolbar to show the sky as seen from your location at the present time. (If the program does not place you at your true location, use the Viewing Location ... command in the Options menu.) Use the Find pane to locate Betelgeuse. If Betelgeuse is below the horizon, allow the program to reset the time to when it is visible. (a) At what time does Betelgeuse rise on today's date? At what time does it set? (b) If Betelgeuse became a supernova today, would it be visible in the daytime? How would it appear at night? Do you think it would cast shadows? (c) Are Betelgeuse and the Moon both in the night sky tonight? (Use the Find pane to locate the Moon.) If they are, and Betelguese were to become a supernova, what kinds of shadows might they both cast?

The Ring Nebula is a planetary nebula in the constellation Lyra. It has an angular size of \(1.4\) arcmin \(\times 1.0\) arcmin and is expanding at the rate of about \(20 \mathrm{~km} / \mathrm{s}\). Approximately how long ago did the central star shed its outer layers? Assume that the nebula is 2,700 ly from Earth.

How is a planetary nebula formed?

How can a supernova continue to shine for many years after it explodes?

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

Recommended explanations on Physics Textbooks

Atoms and Radioactivity

Read Explanation

Electrostatics

Read Explanation

Radiation

Read Explanation

Kinematics Physics

Read Explanation

Engineering Physics

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.

Sign-up for free