Chapter 16
⦁ Describe the two main ways that energy travels through the Sun.
Energy is created through fusion of hydrogen into helium at the center of the Sun. This energy first enters the radiative region of the Sun, where photons are absorbed and reemitted in random directions until they make it about 2/3 of the way to the surface. Once the energy has traveled 2/3 of the way to the surface, it reaches the convection zone where the hot gas flows up and down (like water boiling in a pot) carrying the energy to the solar surface.
⦁ How is a neutrino different from a neutron? List all the ways you can think of.
First, the neutrino's mass is much, much smaller; second, it hardly interacts with matter at all, where as a neutron interacts with other particles; third, it isn't one of the particles to make up an atom; fourth, it can "oscillate" (change from one type of neutrino to another between the Sun's core and Earth).
⦁ What is the ultimate source of energy that makes the Sun shine?
Matter that is converted into energy through the fusion of hydrogen into helium.
⦁ Neutrinos produced in the core of the Sun carry energy to its exterior. Is the mechanism for this energy transport conduction, convection, or radiation?
Since the majority of neutrinos produced inside the Sun do not interact with other particles as they leave the Sun, the energy they carry is transported as radiation.
⦁ What conditions are required before proton-proton chain fusion can start in the Sun
The Sun must be dense and hot enough in the center for the motion of the protons to overcome their mutual repulsion, with a temperature of at least 12 million K.
⦁ Two astronomy students travel to South Dakota. One stands on Earth's surface and enjoys some sunshine. At the same time, the other descends into a gold mine where neutrinos are detected, arriving in time to detect the creation of a new radioactive argon nucleus. Although the photon at the surface and the neutrinos in the mine arrive at the same time, they have had very different histories. Describe the differences.
The neutrino was generated in a fusion reaction in the Sun's core and made it out of the Sun in about 2 seconds and then continued through space until it arrived at Earth about 500 seconds later. Since this neutrino was detected by this process, we know it avoided oscillating and changing into a different kind of neutrino. The photon, which left the Sun's photosphere as sunshine, is "descended" from a gamma-ray photon that was created 100,000 to 1,000,000
⦁ What do measurements of the number of neutrinos emitted by the Sun tell us about conditions deep in the solar interior?
The neutrinos are being produced in the solar core by fusion reactions, and measuring their number gives us a sensitive probe into what is happening in the Sun's core. It helps confirm that there are enough proton-proton chain reactions (each of which produces a neutrino) going on in the Sun's core to explain the energy output of the Sun.
⦁ Describe in your own words what is meant by the statement that the Sun is in hydrostatic equilibrium.
The pressure and gravity are in balance throughout the Sun, from the very center to the surface. This means the gas pressure at any depth within the Sun can support the weight of all of the gas pressing down upon it, due to gravity. So the Sun neither expands nor contracts but remains as it is; this is true at every point within the Sun as well as for the Sun overall.
⦁ Explain how we know that the Sun's energy is not supplied either by chemical burning, as in fires here on Earth, or by gravitational contraction (shrinking).
The vast amount of energy produced by the Sun over the past 4.5 billion years exceeds the amount that could be supplied by burning or shrinking of the Sun by a significant factor. Chemical burning would only last a few thousand years, whereas gravitational contraction would provide energy for only about a hundred million years.
⦁ How do we know the age of the Sun?
Through radioactive dating of rocks, we can determine the age of Earth, the Moon, and meteorites to be about 4.5 billion years. Our models of the formation of the solar system and observations of the formation of other stars with planets tell us that the Sun formed at the same time as the other members of our solar system.
⦁ Do neutrinos have mass? Describe how the answer to this question has changed over time and why.
Yes, they do have mass, and they have always had mass. Human just didn't know that at first. When neutrinos were first proposed by Pauli, physicists thought they were massless particles (all energy).
