Answers

ConceptChecks

ConceptCheck 11-1: It would become a dark nebula because a dark nebula has the same composition as a reflection nebula, but the fine grains of dust comprising it would block out nearly all of the distant starlight if it were compressed to a higher density.

ConceptCheck 11-2: Protostars both gain mass, through dust grain collisions that slow the material causing mass to migrate into the protostar, and simultaneously lose mass, through a T Tauri wind process, during their formation.

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ConceptCheck 11-3: Any compressive physical process that will cause an interstellar cloud of dust and gas to collapse can start the stellar formation process.

ConceptCheck 11-4: Helium atoms are created during the nuclear fusion process of combining hydrogen atoms near the star’s central core.

ConceptCheck 11-5: A shrinking core will have a higher rate of nuclear reactions causing the outer layers to shine more brightly, heat, and expand.

ConceptCheck 11-6: Red dwarfs have convection cells that move fresh hydrogen from the surface into the core for fuel so that nearly all of the hydrogen in a red dwarf can be used for fuel.

ConceptCheck 11-7: Metal-rich stars, like our Sun, are classified as Population I stars.

ConceptCheck 11-8: No. Our Sun is a metal-rich star, which means it was formed from the remains of previously existing stars.

ConceptCheck 11-9: The inward pull of gravity in the most massive of stars compresses the core, making it hotter and more dense, resulting in dramatically higher rates of thermonuclear reactions occurring in the core.

ConceptCheck 11-10: According to Wien’s law, the most common wavelength of light emitted by a glowing object becomes longer, toward the red end of the spectrum, as its temperature decreases.

ConceptCheck 11-11: In a red giant, the core is at a significantly higher temperature and density that allows helium atoms to combine and fuse together, releasing energy.

ConceptCheck 11-12: Normal gases expand when temperature increases, which does not occur in a core of degenerate electrons.

ConceptCheck 11-13: The star is less luminous because a hotter core expands, reducing the temperature of the outer shell, which slows the shell hydrogen fusion reactions, reducing the overall energy output.

ConceptCheck 11-14: Horizontal-branch stars are moving to the left on the H-R diagram and are increasing their temperature, but not changing their luminosity.

ConceptCheck 11-15: No. The core of an AGB star is quite small, about the diameter of planet Earth, not the diameter of Earth’s orbit about the Sun.

ConceptCheck 11-16: None. A planetary nebula results from the ejected outer layers of an aging AGB star and does not involve planets.

ConceptCheck 11-17: The remaining core is composed of carbon and oxygen.

ConceptCheck 11-18: Without slowing due to friction with nearby dust, a planetary nebula will continue to expand indefinitely.

ConceptCheck 11-19: A white dwarf is the smallest, about the size of planet Earth; a brown dwarf is in between, being somewhat larger than a gas giant planet like Jupiter; and a red dwarf is largest, being one of the smallest stable stars.

ConceptCheck 11-20: White-dwarf stars do not change their size as they cool because the electrons are in the degenerate state and the white dwarf cannot contract any further, regardless of temperature.

ConceptCheck 11-21: The evolutionary tracks of a red giant becoming a white dwarf move from right to left as the shrouding planetary nebula diffuses and from upper left to the lower right as the star dims.

CalculationCheck

CalculationCheck 11-1: Gases traveling at 2 × 104 mi/h would take 3 × 109 mi ÷ 2 × 104 mi/h = 1.5 × 105 h to traverse the 3-billion-mile distance from the Sun to Pluto: 1.5 × 105 h ÷ 24 h/day × 6,250 days, or about 17 years.