* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download PREVIEW-Reading Quiz 06 - Chapter 12
Nebular hypothesis wikipedia , lookup
Canis Minor wikipedia , lookup
Corona Australis wikipedia , lookup
Auriga (constellation) wikipedia , lookup
Corona Borealis wikipedia , lookup
Star of Bethlehem wikipedia , lookup
Cassiopeia (constellation) wikipedia , lookup
Dyson sphere wikipedia , lookup
Star catalogue wikipedia , lookup
Cygnus (constellation) wikipedia , lookup
Aquarius (constellation) wikipedia , lookup
Stellar classification wikipedia , lookup
Perseus (constellation) wikipedia , lookup
Timeline of astronomy wikipedia , lookup
H II region wikipedia , lookup
Stellar kinematics wikipedia , lookup
Astronomical spectroscopy wikipedia , lookup
Future of an expanding universe wikipedia , lookup
Corvus (constellation) wikipedia , lookup
Degenerate matter wikipedia , lookup
Reading Quiz 06 - Chapter 12 This is a preview of the published version of the quiz Started: Sep 26 at 10:18am Quiz Instructions Reading Quiz 06 - Chapter 12 of Understanding Our Universe Question 1 1 pts Each of the following supports the statement, "This reasoning tells us that mass determines the structure of a star and its place on the main sequence," except one. Which one should be tossed out as being non-supportive? Higher mass means a stronger force of gravity compressing the star's interior. As a more luminous star ages, its mass increases due to the excess energy it is producing. The higher rate of nuclear fusion means the star will be a more luminous star. The greater force of gravity means the star must produce more outward pressure through nuclear fusion. The higher the luminosity of a star on the main sequence, the shorter its main sequence lifetime. Question 2 1 pts Regulus (constellation Leo) and Barnard's Star (constellation Ophiuchus) are both main sequence stars. Regulus has a mass about 25 times that of Barnard's Star, but will live a much shorter time on the main sequence. Why is that? Regulus has a much smaller fusion core than Barnard's Star and thus has less hydrogen to fuse. Because it is fully convective throughout its interior, Barnard's star can fuse its entire supply of hydrogen. Although Regulus is more massive, it is a rare star that has a much lower fusion rate. Regulus must have a much higher rate of fusion to support itself and runs out of core hydrogen faster. Question 3 1 pts We are going to add some extra explanation of what degeneracy means in a star. "Quantum mechanics restricts the number of electrons that can have low energy. Basically, each electron must occupy its own energy state. When electrons are packed together, as they are in a white dwarf, the number of available low energy states is too small and many electrons are forced into high energy states. When this happens the electrons are said to be degenerate. These high energy electrons make a significant contribution to the pressure. Because the pressure arises from this quantum mechanical effect, it is insensitive to temperature, i.e., the pressure doesn't go down as the star cools. This pressure is known as electron degeneracy pressure and it is the force that supports white dwarf stars against their own gravity." This means only 2 electrons in the lowest energy state (as in the helium atom depicted here, except electrons and nuclei are separated in a white dwarf) and only 8 in the next energy state. Quantum mechanics dictates how many electrons can be packed together. What happens to the degenerate core as more and more mass (helium ash) is piled onto it? Shrinkage of the core to a smaller radius means the force of gravity is stronger. The smaller, more massive core produces higher pressure. Heat coming from the contracting degenerate core increases the shell nuclear fusion. These statements all describe events happening when the helium core becomes degenerate. As more ash is piled onto the core, it actually shrinks. Question 4 Where does the helium flash occur in the figure shown above (which, once it occurs, actually breaks the cycle)? Between E and A Between C and D Between D and E Between B and C Between A and B 1 pts Question 5 1 pts Why do stars become much more luminous while at the same time their surface temperatures are dropping (eventually reaching a minimum temperature) as they move first up the red giant branch and, later, up the asymptotic giant branch? [Hint: Closely study Figure 12.8.] For a sunlike star, the flash expands the core and reduces the star’s luminosity, sending it onto the horizontal branch of the H–R diagram. These stars become more luminous because the degenerate helium or carbon cores continue to grow due to particle pressure. Stars follow the Stefan-Boltzmann law: The higher luminosities generated by the shell fusion makes the star expand enormously, and the increase in radius offsets the decrease in temperature. These stars have cores that are expanding and giving off heat due to conservation of energy. Question 6 1 pts Consider the cores of sun-like stars that are "leaving" the main sequence to the cores of sun-like stars that are "leaving" the horizontal branch. Which one of the following choices does not state a difference? The helium-fusing core of a horizontal branch star had much higher temperatures. Cores of stars leaving the main sequence have helium ash dumped on them; horizontal branch stars, carbon ash. The core of a star leaving the horizontal branch does not experience a "carbon flash." The carbon core of the horizonta branch star never becomes electron degenerate. Question 7 1 pts What characteristic of a giant or an asymptotic giant branch star lead to their eventual loss of around 50% of their mass? Because the surface temperatures of these stars are so low, dust forms along with the gas and gets ejected. The vast majority of these giant stars are part of a binary system and mass ends up being dumped on the other star. These giant stars have convection occurring throughout their interior, and this motion causes gas ejection. These stars are so huge that the force of gravity at their surfaces is less than the outward thermal pressure. Question 8 1 pts Refer back to the sections about light in Chapter 10 of our textbook. Planetary nebulae provide excellent examples of the range colors that can be produced by processes occurring in atoms. (The colors displayed for the images of the planetary nebulae in the text may, in fact, be the actual colors.) What kind of spectra do we expect to see from planetary nebulae? Emission Continuous, absorption, and emission on top of each other. Continuous Absorption Question 9 1 pts The hot carbon core of the once sun-like star is about the size of Earth but extremely hot - 100,000 Kelvin or more. What does this imply about the source of energy, the photons, that is exciting the gases of planetary nebulae? The radiation from the white dwarf follow Wien's Law: Ultraviolet photons are being created and they excite the gases. Many trillions of photons at radio wavelengths are created every second. The white dwarf is spinning exceedingly fast and that excites the gases of the nebulae. The high velocities and thus kinetic energy of the ejected gases cause them to glow. Question 10 1 pts If we were able to observe a cluster of stars from when the stars were 5 billion years old until they were 12 billion years old, what would we observe about the overall luminosities and temperatures of the stars that are still on the main sequence as the cluster aged? Both the luminosities and temperatures of stars would decrease as lower mass stars are all that are left on the main sequence. The stars on the main sequence would still represent the entire range of luminosities and temperatures as the cluster aged. Stars still on the main sequence would be those having the highest luminosities but lowest temperatures. The temperatures of the stars would get higher while their luminosities decreased. Saving... Submit Quiz