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 planetary nebula. B) as a protostar. C) as a red giant or supergiant. D) as a main sequence star. E) as a T Tauri variable star. 1) 2) When a star's inward gravity and outward pressure are balanced, the star is said to be A) a stage 2 protostar. B) in rotational equilibrium. C) in hydrostatic equilibrium. D) in gravitational collapse. E) in thermal expansion. 2) 3) What spectral type of star that is still around formed longest ago? A) O B) M C) F D) K E) A 3) 4) What spectral type of star that is still around formed most recently? A) O B) M C) K D) A E) F 4) 5) At which stage in a sun-like star's life is its core the least dense? A) White Dwarf B) Helium Fusion C) Subgiant Branch D) Planetary Nebula E) Main Sequence 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) hydrogen C) carbon D) aluminum E) calcium 6) 1

2 7) What temperature is needed to fuse helium into carbon? A) 15 million K B) 100 million K C) one billion K D) 5,800 K E) 100,000 K 7) 8) The "helium flash" occurs at what stage in stellar evolution? A) red giant B) in the middle of the main sequence stage C) horizontal branch D) when the T Tauri bipolar jets shoot out E) planetary nebula 8) 9) During the hydrogen shell burning phase A) helium is burning in the core. B) the core is expanding. C) hydrogen is burning in the central core. D) the star becomes less luminous. E) the star grows more luminous. 9) 10) A star is on the horizontal branch of the H-R diagram. Which statement is true? A) The star is about to return to the main sequence. B) It is burning only helium. C) It is burning both hydrogen and helium. D) It is about to experience the helium flash. E) The star is contracting. 10) 11) What inevitably forces a star like the Sun to evolve away from being a main sequence star? A) Helium builds up in the core, while the hydrogen burning shell expands. B) The core begins fusing iron. C) The carbon detonation explodes it as a type I supernova. D) The star uses up all its supply of hydrogen. E) The core loses all its neutrinos, so all fusion ceases. 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) Its outer envelope is stripped away and we see the brilliant core. C) It explodes. D) Helium fusion gives more energy than hydrogen fusion does, based on masses. E) It immediately starts to fuse helium. 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) asymptotic giant branch C) planetary nebula D) white dwarf 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) asymptotic giant branch B) white dwarf C) red giant branch D) planetary nebula E) horizontal branch 14) 15) Refer to the figure above. What is the name of the star labeled 10? A) asymptotic giant branch B) horizontal branch C) planetary nebula D) red giant branch E) white dwarf 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) 8 D) 11 E) 9 16) 17) A solar mass star will evolve off the main sequence when A) it explodes as a violent nova. B) it expels a planetary nebula to cool off and release radiation. C) it loses all its neutrinos, so fusion must cease. D) it completely runs out of hydrogen. E) it builds up a core of inert helium. 17) 18) What is a planetary nebula? A) the disc of gas and dust surrounding a young star that will soon form a solar system B) a planet surrounded by a glowing shell of gas 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 bipolar jets ejected by a T Tauri variable 18) 19) What are black dwarfs? A) pulsars that have slowed down and stopped spinning B) the end result of massive star evolution C) objects that are not quite massive enough to be stars D) cooled off white dwarfs that no longer glow visibly E) the lowest mass main sequence stars 19) 20) The order of evolutionary stages of a star like the Sun would be Main Sequence, giant, planetary nebula, and finally: A) nova. B) white dwarf. C) black hole. D) hypernova. E) neutron star. 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 a million times higher density. C) a larger mass and a 100 times lower density. D) about the same mass and density. E) a smaller mass and and half the 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) white dwarf C) horizontal branch D) asymptotic giant branch E) red 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) white dwarf C) planetary nebula D) asymptotic giant branch E) horizontal branch 23) 24) Which of these will the Sun probably become in the very distant future? A) nova B) pulsar C) planetary nebula D) hypernova E) supernova 24) 5

6 25) Which of the following is true regarding planetary nebulae? A) Some are spherical, but most have bipolar structure. B) They are the ejected envelopes of highly evolved brown dwarf stars. C) They are the result of the mass loss during the main sequence stage of the most massive stars. D) They are the coronas surrounding most blue stragglers. E) They are the rings of material surrounding newly formed stars that will eventually form the planetary systems. 25) 26) Virtually all the carbon-rich dust in the plane of the galaxy originated in A) white dwarfs. B) high-mass stars. C) planetary nebulae. D) low-mass stars. E) brown dwarfs. 26) 27) A high-mass star dies more violently than a low-mass star because: A) it generates more heat and its core eventually collapses very suddenly. B) it is most often found as part of a binary system. C) gravity is weakened by its high luminosity. D) it must always end up as a black hole. E) it cannot fuse elements heavier than carbon. 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 they can also have strong stellar winds B) because their masses will decrease as they fuse heavy elements into lighter elements in their cores C) because about half that mass will be contained in the carbon core D) because these stars will eject at least 4 solar masses in the planetary nebula stage E) because they would be classified as brown dwarfs 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) horizontally right, then forms a clockwise loop C) vertically upward, along the left edge of the diagram D) horizontally right, diagonally to lower left, then horizontally right E) diagonally to lower right, then vertical, then horizontally left 29) 30) Which of the following best describes the evolutionary track of the most massive stars? A) horizontal right B) vertically left, then straight down C) diagonally to lower right, then vertical, then horizontal left D) horizontally right, diagonal to lower left, then 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) decreases. B) remains roughly constant. C) first increases, then decreases. D) increases. 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 needed for carbon fusing into heavier elements. B) It is the temperature at which helium fuses into carbon. 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) red giants. B) Cepheid variables. C) T Tauri variables. D) massive blue main sequence stars. E) yellow main sequence stars like the Sun. 33) 34) What characteristic of a star cluster is used to determine its age? A) the faintest stars seen in the cluster B) the ratio of main sequence to white dwarfs stars C) the main sequence turnoff D) the total number of stars in the cluster E) the number of red giants 34) 35) What is the typical age for a globular cluster associated with our Milky Way? A) 200 million years B) 45 billion years C) a few million years D) billion years E) a billion years 35) 36) The brightest stars in a young open cluster will be A) red giants that are fusing helium into carbon. B) yellow giants like our Sun, but much larger. C) the core stars of planetary nebulae. D) massive blue stars at the top left on the H-R diagram. 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) further away. B) less obscured by dust. C) younger. D) more obscured by dust. E) older. 37) 7

8 38) What is a typical age for a globular cluster? A) 200 million years B) 4.8 billion years C) 10 million years D) one billion years E) 12 billion years 38) 39) In globular clusters, the brightest stars will be A) massive blue main sequence stars. B) red supergiants. C) planetary nebulae. D) blue stragglers. E) T Tauri stars. 39) 40) In a fairly young star cluster, if the most massive stars are swelling up into giants, the least massive stars are A) collapsing directly to white dwarfs. B) also evolving off the main sequence as well. C) blowing off shells as planetary nebula instead. D) still evolving toward their ZAMS positions. E) continuing to shine as stable main sequence stars. 40) 41) The brightest stars in aging globular clusters will be A) red supergiants like Betelguese and Antares. B) blue supergiants like Rigel and Deneb. C) massive blue main sequence stars like Spica. D) core stars of planetary nebulae. E) blue stragglers. 41) 42) Noting the turnoff mass in a star cluster allows you to determine its A) radial velocity. B) distance. C) number of stars. D) total mass. E) age. 42) 43) Which is used observationally to determine the age of a star cluster? A) the total number of main sequence stars B) the amount of dust that lies around the cluster C) the number of white dwarfs D) the luminosity of the main sequence turn-off point E) the ratio of giants to supergiants 43) 44) What is the unusual result of mass transfer in the Algol binary system? A) a carbon white dwarf B) a helium white dwarf C) a red dwarf D) a brown dwarf E) a black 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 the part of a rapidly rotating star that will eventually spin away to form planets. E) is, in terms of the star's gravity, its "zone of influence." 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) Aldeberan. B) Antares. C) Altair. D) Algol. E) Alberio. 46) 47) Mass transfer in binaries occurs when one giant swells to reach the A) Cassini Division. B) Roche Lobe. C) Chandrasekhar Limit. D) Hayashi Track. E) Herbig-Haro Limit. 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 Sirius A will be stable three times longer than Sirius B. B) that there should be a planetary nebula around the Sirius system. C) the Sirius A will end up as a black hole, not a white dwarf like its companion. D) that white dwarfs evolve slower than main sequence stars. E) that the collapsed companion transferred mass to Sirius A. 48) 49) You observe a low-mass helium white dwarf. What can you conclude? A) It is part of a binary star system. B) It will soon be a planetary nebula. C) It was once a blue supergiant. D) It is over 100 billion years old. E) Its core is mostly carbon. 49) 50) Which stars in globular clusters are believed to be examples of mergers? A) blue stragglers B) planetary nebulae cores C) blue supergiants D) eclipsing binaries E) brown dwarfs 50) 9