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Chapter 14: Problem 16

Explain how hydrostatic equilibrium acts as a safety valve to keep the Sun at its constant size, temperature, and luminosity.

Short Answer

Expert verified
Hydrostatic equilibrium balances gravitational force and thermal pressure, keeping the Sun stable in size, temperature, and luminosity.

Step by step solution

01

Understanding Hydrostatic Equilibrium

Hydrostatic equilibrium is a balance between the inward gravitational force and the outward pressure produced by the energy generated in the Sun’s core. This balance keeps the Sun stable in size.
02

Gravitational Force

The Sun's gravity tries to pull all its mass toward the center. This inward force would cause the Sun to collapse if it were unopposed.
03

Outward Pressure

The energy produced in the core of the Sun results in thermal pressure. This pressure pushes outward and opposes the gravitational force.
04

Dynamic Balance

When these two forces are equal, the Sun is in hydrostatic equilibrium. This equilibrium acts like a safety valve, ensuring the Sun does not expand or contract drastically.
05

Temperature and Luminosity

This balance also ensures that the Sun maintains a consistent temperature and luminosity. If the Sun were to expand, the outer layers would cool, decreasing pressure until equilibrium is reestablished.
06

Stability

Hydrostatic equilibrium keeps the Sun stable by adjusting its internal conditions to resist changes in size, temperature, and luminosity.

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Key Concepts

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

gravitational force in stars
In any star, including the Sun, gravity plays a vital role. This force pulls all mass towards the star’s center. Imagine gravity as a giant invisible hand that continually presses inward, trying to compress the star.
Without any opposition, this force would lead to the collapse of the star under its own weight.
Gravity is more intense in stars with greater mass. The more massive a star is, the stronger the gravitational pull it has. This inward pull is crucial because it creates the conditions needed for nuclear fusion to occur in the star's core.
For our Sun:
  • Gravity tries to pull the Sun’s mass inward.
  • This force becomes stronger the closer you get to the core.
thermal pressure in stars
Stars have a powerful mechanism to counteract the inward pull of gravity: **thermal pressure**. This type of pressure is generated by the energy produced through nuclear fusion in the star’s core. As the core’s temperature rises due to fusion, this heat creates an outward pressure.
Think of thermal pressure as the response to gravity's inward push.
Here's how it works in the Sun:
  • Nuclear fusion in the core converts hydrogen into helium, generating a massive amount of energy.
  • This energy heats up the particles, causing them to move rapidly and create outward pressure.
  • This pressure pushes against the inward gravitational force.
When thermal pressure balances out the gravitational force, it's a process known as hydrostatic equilibrium.
stellar stability
Stellar stability is the result of a delicate balance within stars. The Sun remains stable thanks to hydrostatic equilibrium, which acts like a cosmic safety valve. It ensures the star doesn't expand or contract uncontrollably.
Here's what maintains a star's stability:
  • Hydrostatic Equilibrium: The balance between gravitational force and thermal pressure keeps the star's size constant.
  • Temperature Regulation: If a star starts to expand, its outer layers cool, reducing pressure until equilibrium is restored.
  • Luminosity Consistency: A stable equilibrium means the star maintains a consistent brightness and temperature.
This balance is dynamic:
  • If there is any disturbance, internal adjustments trigger to restore equilibrium.
  • This process ensures long-term stability and prevents drastic changes in size, temperature, or luminosity.
In essence, hydrostatic equilibrium is what enables stars to shine steadily for billions of years.

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Most popular questions from this chapter

As energy moves out from the Sun's core toward its surface, it first travels by __________ then by ________ and then by __________ . a. radiation; conduction; radiation b. conduction; radiation; convection c. radiation; convection; radiation d. radiation; convection; conduction

The solar corona has a temperature of 1 million to 2 million \(K\) the photosphere has a temperature of only about \(6000 \mathrm{K}\) Why isn't the corona much, much brighter than the photosphere? a. The magnetic field traps the light. b. The corona emits only X-rays. c. The photosphere is closer to us. d. The corona has a much lower density.

On average, how long does it take particles in the solar wind to reach Earth from the Sun if they are traveling at an average speed of \(400 \mathrm{km} / \mathrm{s} ?\)

Sunspots change in number and location during the solar cycle. This phenomenon is connected to a. the rotation rate of the Sun. b. the temperature of the Sun. c. the magnetic field of the Sun. d. the tilt of the axis of the Sun.

The hydrogen bomb represents an effort to create a similar process to what takes place in the core of the Sun. The energy released by a 5-megaton hydrogen bomb is \(2 \times 10^{16} \mathrm{J}\) a. This textbook, \(21^{\text {th }}\) Century Astronomy, has a mass of about 1.6 kg. If all of its mass were converted into energy, how many 5 -megaton bombs would it take to equal that energy? b. How much mass did Earth lose each time a 5-megaton hydrogen bomb was exploded?
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