ASTR Fall Semester Joel E. Tohline, Alumni Professor Office: 247 Nicholson Hall [Slides from Lecture08]

Chapter 16: Our Star, the Sun

Chapter Overview The Sun’s Interior –16-1: The source of the Sun’s heat and light –16-2: How scientists model the Sun’s internal structure –16-3: How the Sun’s vibrations reveal what lies beneath its glowing surface –16-4: How scientists are able to probe the Sun’s energy-generating core This is the textbook material on which I will focus.

Sun’s Internal Structure Figure 16-4

Modeling the Sun’s Interior 1.Hydrostatic Equilibrium 2.Thermal Equilibrium 3.Energy from nuclear fusion (E = mc 2 )

Modeling the Sun’s Interior Hydrostatic Equilibrium –Gas pressure force (directed outward) balances force of gravity (directed inward) throughout the interior –If not balanced, Sun’s structure should change appreciably in a matter of hours!

Modeling the Sun’s Interior Hydrostatic Equilibrium –Gas pressure force (directed outward) balances force of gravity (directed inward) throughout the interior –If not balanced, Sun’s structure should change appreciably in a matter of hours!

Modeling the Sun’s Interior Thermal Equilibrium –Sun is steadily losing energy at its surface (it’s shining!); it is trying to “cool off” –Heat from the Sun’s interior slowly diffuses toward the surface –This lost heat can be replenished by slow gravitational contraction (whenever a gas is compressed, its temperature rises); this is referred to as “Kelvin-Helmholtz contraction” ( see §16-1 ) –If Kelvin-Helmholtz contraction is responsible for keeping the Sun’s interior hot, the Sun’s structure should change appreciably on a time scale of ~ 10 million years

Modeling the Sun’s Interior Thermal Equilibrium –Sun is steadily losing energy at its surface (it’s shining!); it is trying to “cool off” –Heat from the Sun’s interior slowly diffuses toward the surface –This lost heat can be replenished by slow gravitational contraction (whenever a gas is compressed, its temperature rises); this is referred to as “Kelvin-Helmholtz contraction” ( see §16-1 ) –If Kelvin-Helmholtz contraction is responsible for keeping the Sun’s interior hot, the Sun’s structure should change appreciably on a time scale of ~ 10 million years

Modeling the Sun’s Interior Thermal Equilibrium –Sun is steadily losing energy at its surface (it’s shining!); it is trying to “cool off” –Heat from the Sun’s interior slowly diffuses toward the surface Radiative diffusion (diffusion of light) Convection (“boiling”) Timescale: It takes approximately 170,000 years for energy created at the Sun’s center to travel to and escape from the surface of the Sun!

Modeling the Sun’s Interior Thermal Equilibrium –Sun is steadily losing energy at its surface (it’s shining!); it is trying to “cool off” –Heat from the Sun’s interior slowly diffuses toward the surface –This lost heat can be replenished by slow gravitational contraction (whenever a gas is compressed, its temperature rises); this is referred to as “Kelvin-Helmholtz contraction” ( see §16-1 ) –If Kelvin-Helmholtz contraction is responsible for keeping the Sun’s interior hot, the Sun’s structure should change appreciably on a time scale of ~ 10 million years

Modeling the Sun’s Interior Thermal Equilibrium –Sun is steadily losing energy at its surface (it’s shining!); it is trying to “cool off” –Heat from the Sun’s interior slowly diffuses toward the surface –This lost heat can be replenished by slow gravitational contraction (whenever a gas is compressed, its temperature rises); this is referred to as “Kelvin-Helmholtz contraction” ( see §16-1 ) –If Kelvin-Helmholtz contraction is responsible for keeping the Sun’s interior hot, the Sun’s structure should change appreciably on a time scale of ~ 10 million years

A Problem with Time Scales!

Chemical Elements & Their Isotopes Courtesy of:

Chemical Elements & Their Isotopes Hydrogen

Chemical Elements & Their Isotopes Hydrogen

Chemical Elements & Their Isotopes Helium

Chemical Elements & Their Isotopes Helium

Chemical Elements & Their Isotopes Carbon

Chemical Elements & Their Isotopes Carbon

Chart of Nuclides

C 14

Chart of Nuclides C = 14