Astronomy: Chapter 7

Question 1

Describe the roles of convection, conduction, and radiation in the interiors of stars.

Answer 1

• Conduction: most familiar form of heat flow. requires close contact between the atoms. only important in rare types of stars with extremely high densities.
• Radiation: is the principal means of energy transport in the interiors of most stars. Photons are absorbed and re-emitted at random directions over and over as energy works its way from the hot interior toward the cooler surface.
• Convection: energy is carried upward as rising hot gas and also sinking cool gas.

Question 2

Explain the four laws of stellar structure.

Answer 2

• The first two laws are conservation laws: certain things cannot be created out of nothing or vanish into nothing.
  
  • conservation of mass: total mass of the star must equal the sum of the masses of its shells.
  • Conservation of energy: total luminosity equals the sum of energy generated in all of the layers.
  • Hydrostatic equilibrium: fluid; the weight of each layer is balanced by the pressure in that layer.
  • energy transport: energy must flow from hot regions to cool regions either by conduction, convection, or radiation.

Question 3

Describe the process of nuclear fusion in some detail.

Answer 3

• Nuclear fusion is the process by which multiple atomic nuclei join together to form a single heavier nucleus. It is accompanied by the release or absorption of energy.
• takes place at very high temperatures at 10^7K
• Nuclear fusion reaction is called THERMAL NUCLEAR REACTION
• Nuclear fusion is the type of reaction taking place in the sun. inside the suns core, fast moving hydrogen nuclei combine to form “He” nucleus.
• Massive stars fuse hydrogen, then helium and develop carbon-oxygen cores. At 1 billion K, they are able to ignite carbon, then oxygen, neon, and magnesium fuse to make silicon, which finally fuses to make iron.
• because more and more protons are used up to make heavier atoms and progressively less energy is released, fusion proceeds at higher and higher rate.

Question 4

What was the “missing neutrino problem” and how was it solved.

Answer 4

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Question 5

List and describe the different kinds of interstellar nebulae and describe the causes of their various colors.

Answer 5

• Emission Nebulae: produced when a hot star excites the gas near it to produce an emission spectrum. Star must be hotter than about B1 (25,000K). Emission nebulae have a distinctive pink color produced by the blending of the red, blue, and violet Balmer Lines.
• Reflection Nebula: produced when starlight scatters from a dusty nebula. Looks blue because short wavelengths scatter more easily than long wavelengths. Gas is surely present in a reflection nebula, but it is not excited to emit photons.
• Dark Nebula: dense clouds of gas and dust that obstruct the view of more distant stars.

Question 6

List and briefly describe the components of the interstellar medium.

Answer 6

• Interstellar Medium (ISM): the gas and dust distributed between the stars.
• About 75% of the mass of interstellar gas is hydrogen
• About 25% is helium; there are also traces of Carbon, nitrogen, oxygen, calcium, sodium, and heavier atoms.
• About 1% of ISM mass is made up of microscopic particles called interstellar dust. dust seems to be made mostly of carbon and silicates.
• ISM, in some cases, can easily be seen as clouds of gas or dust also known as a nebula.

Question 7

What is meant by the “pressure-temperature” thermostat, and how does it work?

Answer 7

• The “pressure-temperature” thermostat is a natural thermostat that keeps the reactions from erupting out of control.
• It balances energy with the inward pull of gravity.
• It is a built in regulator that keeps the nuclear reactions from occurring too rapidly.
• Also keeps reactions from dying down.

Question 8

Describe the stages in the formation of a new star.

Answer 8

• Stars can form n molecular clouds, a dense interstellar gas cloud in which atoms are able to link together to form molecules such as H2 or CO, when the densest part of clouds become unstable and contract under the influence of their own gravity.
• Protostar: a collapsing cloud of gas and dust destined to become a star.
  
  • a shockwave (red) approaches a interstellar gas cloud.
  • the shockwave passes through and compresses the cloud.
  • the densest part of the cloud become gravitationally unstable.
  • approximately 6 million years later, contracting regions of gas gives birth to stars.

Question 9

Describe the evidence of star formation in the Orion nebula

Answer 9

• Orion is filled with young stars because it contains a large number of t-stars.