Astronomy Ch. 20 Stellar Evolution. MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.

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1 Name: Period: Date: Astronomy Ch. 20 Stellar Evolution MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) A star (no matter what its mass) spends most of its life: A) as a protostar. B) as a red giant or supergiant. C) as a main sequence star. D) as a T Tauri variable star. E) as a planetary nebula. 1) 2) When a star's inward gravity and outward pressure are balanced, the star is said to be A) in hydrostatic equilibrium. B) in thermal expansion. C) in rotational equilibrium. D) in gravitational collapse. E) a stage 2 protostar. 2) 3) What spectral type of star that is still around formed longest ago? A) A B) M C) K D) O E) F 3) 4) What spectral type of star that is still around formed most recently? A) O B) M C) A D) K E) F 4) 5) At which stage in a sun-like star's life is its core the least dense? A) Planetary Nebula B) White Dwarf C) Main Sequence D) Helium Fusion E) Subgiant Branch 5) 6) Which of the following elements contained in your body is NOT formed in the cores of stars during thermonuclear fusion? A) iron B) aluminum C) hydrogen D) carbon E) calcium 6) 1

2 7) What temperature is needed to fuse helium into carbon? A) 5,800 K B) 100 million K C) one billion K D) 15 million K E) 100,000 K 7) 8) The "helium flash" occurs at what stage in stellar evolution? A) in the middle of the main sequence stage B) when the T Tauri bipolar jets shoot out C) horizontal branch D) planetary nebula E) red giant 8) 9) During the hydrogen shell burning phase A) helium is burning in the core. B) the star grows more luminous. C) hydrogen is burning in the central core. D) the star becomes less luminous. E) the core is expanding. 9) 10) A star is on the horizontal branch of the H-R diagram. Which statement is true? A) It is burning only helium. B) It is burning both hydrogen and helium. C) The star is contracting. D) The star is about to return to the main sequence. E) It is about to experience the helium flash. 10) 11) What inevitably forces a star like the Sun to evolve away from being a main sequence star? A) The star uses up all its supply of hydrogen. B) The core loses all its neutrinos, so all fusion ceases. C) The core begins fusing iron. D) Helium builds up in the core, while the hydrogen burning shell expands. E) The carbon detonation explodes it as a type I supernova. 11) 12) Just as a low-mass main sequence star runs out of fuel in its core, it actually becomes brighter. How is this possible? A) The core contracts, raising the temperature and increasing the size of the region of hydrogen shell-burning. B) It explodes. C) It immediately starts to fuse helium. D) Helium fusion gives more energy than hydrogen fusion does, based on masses. E) Its outer envelope is stripped away and we see the brilliant core. 12) 2

3 13) Refer to the figure above. What is the name of the path between the points labeled 8 and 9? A) horizontal branch B) white dwarf C) planetary nebula D) asymptotic giant branch E) red giant branch 13) 14) Refer to the figure above. What is the name of the path between the points labeled 10 and 11? A) red giant branch B) asymptotic giant branch C) planetary nebula D) horizontal branch E) white dwarf 14) 15) Refer to the figure above. What is the name of the star labeled 10? A) planetary nebula B) red giant branch C) white dwarf D) asymptotic giant branch E) horizontal branch 15) 3

4 16) Refer to the figure above. At what numbered point on the graph above does the helium flash occur? A) 10 B) 7 C) 9 D) 11 E) 8 16) 17) A solar mass star will evolve off the main sequence when A) it builds up a core of inert helium. B) it loses all its neutrinos, so fusion must cease. C) it expels a planetary nebula to cool off and release radiation. D) it completely runs out of hydrogen. E) it explodes as a violent nova. 17) 18) What is a planetary nebula? A) a planet surrounded by a glowing shell of gas B) the bipolar jets ejected by a T Tauri variable C) a type of young, medium mass star D) the ejected envelope, often bipolar, of a red giant surrounding a stellar core remnant E) the disc of gas and dust surrounding a young star that will soon form a solar system 18) 19) What are black dwarfs? A) the lowest mass main sequence stars B) cooled off white dwarfs that no longer glow visibly C) pulsars that have slowed down and stopped spinning D) objects that are not quite massive enough to be stars E) the end result of massive star evolution 19) 20) The order of evolutionary stages of a star like the Sun would be Main Sequence, giant, planetary nebula, and finally: A) neutron star. B) hypernova. C) nova. D) black hole. E) white dwarf. 20) 21) Compared to our Sun, a typical white dwarf has A) a smaller mass and twice the density. B) about the same mass and density. C) a smaller mass and and half the density. D) a larger mass and a 100 times lower density. E) about the same mass and a million times higher density. 21) 4

5 22) Refer to the figure above. What is the name of the path between the points labeled 11 and 12? A) planetary nebula B) red giant branch C) white dwarf D) horizontal branch E) asymptotic giant branch 22) 23) Refer to the figure above. What is the name of the path between the points labeled 13 and 14? A) red giant branch B) asymptotic giant branch C) planetary nebula D) horizontal branch E) white dwarf 23) 24) Which of these will the Sun probably become in the very distant future? A) planetary nebula B) pulsar C) nova D) hypernova E) supernova 24) 5

6 25) Which of the following is true regarding planetary nebulae? A) They are the rings of material surrounding newly formed stars that will eventually form the planetary systems. B) They are the result of the mass loss during the main sequence stage of the most massive stars. C) They are the coronas surrounding most blue stragglers. D) Some are spherical, but most have bipolar structure. E) They are the ejected envelopes of highly evolved brown dwarf stars. 25) 26) Virtually all the carbon-rich dust in the plane of the galaxy originated in A) planetary nebulae. B) brown dwarfs. C) high-mass stars. D) low-mass stars. E) white dwarfs. 26) 27) A high-mass star dies more violently than a low-mass star because: A) it is most often found as part of a binary system. B) it must always end up as a black hole. C) it generates more heat and its core eventually collapses very suddenly. D) it cannot fuse elements heavier than carbon. E) gravity is weakened by its high luminosity. 27) 28) Isolated main-sequence stars as massive as 10 to 12 times the mass of the sun may still manage to avoid going supernova. Why? A) because these stars will eject at least 4 solar masses in the planetary nebula stage B) because their masses will decrease as they fuse heavy elements into lighter elements in their cores C) because they can also have strong stellar winds D) because they would be classified as brown dwarfs E) because about half that mass will be contained in the carbon core 28) 29) Which of the following best describes the evolutionary track followed on the H-R diagram for the most massive stars? A) horizontally right B) diagonally to lower right, then vertical, then horizontally left C) horizontally right, diagonally to lower left, then horizontally right D) vertically upward, along the left edge of the diagram E) horizontally right, then forms a clockwise loop 29) 30) Which of the following best describes the evolutionary track of the most massive stars? A) vertically left, then straight down B) diagonally to lower right, then vertical, then horizontal left C) horizontally right, diagonal to lower left, then horizontal right D) horizontal right E) horizontal right, then a clockwise loop 30) 6

7 31) As a 4-10 solar mass star leaves the main sequence on its way to becoming a red supergiant, its luminosity A) increases. B) decreases. C) remains roughly constant. D) first increases, then decreases. E) first decreases, then increases. 31) 32) In the evolution of massive stars, what is the significance of the temperature 600 million K? A) It is the temperature at which helium fuses into carbon. B) It is the temperature needed for carbon fusing into heavier elements. C) It is the temperature needed for helium burning into boron. D) It is the final temperature reached during their evolution. E) It is the main sequence core temperature which makes massive stars so bright. 32) 33) The brightest stars of a young open cluster will be A) Cepheid variables. B) massive blue main sequence stars. C) yellow main sequence stars like the Sun. D) T Tauri variables. E) red giants. 33) 34) What characteristic of a star cluster is used to determine its age? A) the faintest stars seen in the cluster B) the total number of stars in the cluster C) the number of red giants D) the main sequence turnoff E) the ratio of main sequence to white dwarfs stars 34) 35) What is the typical age for a globular cluster associated with our Milky Way? A) billion years B) 45 billion years C) 200 million years D) a billion years E) a few million years 35) 36) The brightest stars in a young open cluster will be A) the core stars of planetary nebulae. B) red giants that are fusing helium into carbon. C) massive blue stars at the top left on the H-R diagram. D) yellow giants like our Sun, but much larger. E) red T-tauri stars still heading for the main sequence. 36) 37) Compared to a cluster containing type O and B stars, a cluster with only type F and cooler stars will be A) less obscured by dust. B) further away. C) more obscured by dust. D) younger. E) older. 37) 7

8 38) What is a typical age for a globular cluster? A) 200 million years B) 10 million years C) 12 billion years D) one billion years E) 4.8 billion years 38) 39) In globular clusters, the brightest stars will be A) red supergiants. B) massive blue main sequence stars. C) T Tauri stars. D) blue stragglers. E) planetary nebulae. 39) 40) In a fairly young star cluster, if the most massive stars are swelling up into giants, the least massive stars are A) also evolving off the main sequence as well. B) collapsing directly to white dwarfs. C) blowing off shells as planetary nebula instead. D) continuing to shine as stable main sequence stars. E) still evolving toward their ZAMS positions. 40) 41) The brightest stars in aging globular clusters will be A) red supergiants like Betelguese and Antares. B) massive blue main sequence stars like Spica. C) blue stragglers. D) core stars of planetary nebulae. E) blue supergiants like Rigel and Deneb. 41) 42) Noting the turnoff mass in a star cluster allows you to determine its A) distance. B) radial velocity. C) total mass. D) age. E) number of stars. 42) 43) Which is used observationally to determine the age of a star cluster? A) the ratio of giants to supergiants B) the amount of dust that lies around the cluster C) the total number of main sequence stars D) the luminosity of the main sequence turn-off point E) the number of white dwarfs 43) 44) What is the unusual result of mass transfer in the Algol binary system? A) a black dwarf B) a brown dwarf C) a helium white dwarf D) a carbon white dwarf E) a red dwarf 44) 8

9 45) The Roche lobe of a star in a binary star system A) leads to formation of rings, like around the jovian planets. B) resembles the ear of Edouard Roche, a French mathematician. C) is the accretion disc around the companion star. D) is, in terms of the star's gravity, its "zone of influence." E) is the part of a rapidly rotating star that will eventually spin away to form planets. 45) 46) The most famous case of a more massive hot star orbiting with a more evolved but presently less massive red giant is the eclipsing binary A) Antares. B) Alberio. C) Altair. D) Algol. E) Aldeberan. 46) 47) Mass transfer in binaries occurs when one giant swells to reach the A) Chandrasekhar Limit. B) Roche Lobe. C) Cassini Division. D) Herbig-Haro Limit. E) Hayashi Track. 47) 48) That brighter Sirius A weighs 3 solar masses, but the white dwarf Sirius B is only about one solar mass implies: A) that there should be a planetary nebula around the Sirius system. B) that the collapsed companion transferred mass to Sirius A. C) that Sirius A will be stable three times longer than Sirius B. D) that white dwarfs evolve slower than main sequence stars. E) the Sirius A will end up as a black hole, not a white dwarf like its companion. 48) 49) You observe a low-mass helium white dwarf. What can you conclude? A) It was once a blue supergiant. B) It is part of a binary star system. C) Its core is mostly carbon. D) It is over 100 billion years old. E) It will soon be a planetary nebula. 49) 50) Which stars in globular clusters are believed to be examples of mergers? A) eclipsing binaries B) brown dwarfs C) planetary nebulae cores D) blue supergiants E) blue stragglers 50) 9