Astronomy Exam 3 Ch 10-14
Helium fusion results in the production of
A: hydrogen. B: carbon. C: nitrogen. D: iron. E: oxygen. B: Carbon
The faintest star visible to the naked eye has an apparent magnitude of about
A: 1 B: -1 C: 10 D: 0 E: 6 E: 6
What percentage of a star's total lifetime is spent on the main sequence?
A: 10% B: 90% C: 100% D: 50% E: 20% B: 90%
Which is closest to the temperature of the Sun's core?
A: 100 million K B: 1 million K C: 10 million K D: 10,000 K E: 100,000 K C: 10 million K
At least ________ % of stars host at least one planet.
A: 30 B: 1 C: 70 D: 10 C: 70
How many helium nuclei fuse together when making carbon?
A: 4 B: 2 C: 3 D: it varies depending on the reaction E: helium cannot fuse into carbon C: 3
How much mass does the Sun lose through nuclear fusion per second?
A: 600 tons B: 4 tons C: 4 million tons D: 600 million tons E: Nothing; mass-energy is conserved. C: 4 million tons
Which of the following statements about novae is not true?
A: A star system that undergoes a nova may have another nova sometime in the future. B: Our Sun will probably undergo at least one nova when it becomes a white dwarf about 5 billion years from now. C: The word nova means "new star" and originally referred to stars that suddenly appeared in the sky, then disappeared again after a few weeks or months. D: A nova involves fusion taking place on the surface of a white dwarf. E: When a star system undergoes a nova, it brightens considerably, but not as much as a star system undergoing a supernova. B: Our Sun will probably undergo at least one nova when it becomes a white dwarf about 5 billion years from now.
Suppose a white dwarf is gaining mass because of accretion from a binary companion. What happens if its mass reaches the 1.4 solar mass limit?
A: A white dwarf can never gain enough mass to reach the limit because a strong stellar wind prevents the accreting material from reaching it in the first place. B: The white dwarf undergoes a collapse and expels the excess mass in a nova eruption. C: The white dwarf (which is made mostly of carbon) suddenly detonates carbon fusion and this creates a white dwarf supernova explosion. D: The white dwarf immediately collapses into a black hole, disappearing from view. C: The white dwarf (which is made mostly of carbon) suddenly detonates carbon fusion and this creates a white dwarf supernova explosion.
Planets detected via the Doppler technique have been mostly
A: Earth-mass, in Earth-like orbits. B: a wide range of masses, in edge-on orbits. C: Jupiter-mass, in Jupiter-like orbits. D: Earth-mass, in very close orbits. E: Jupiter-mass, in very close orbits. E: Jupiter-mass, in very close orbits.
How are elements beyond iron formed in massive-star supernovae?
A: Elements thrown out at high speeds fuse with hydrogen atoms in the interstellar medium. B: Neutrons produced during the core collapse are slammed into atomic nuclei. C: The high temperature and pressure allow iron nuclei to fuse. B: Neutrons produced during the core collapse are slammed into atomic nuclei.
Which of the following statements about black holes is not true?
A: If the Sun magically disappeared and was replaced by a black hole of the same mass, the Earth would soon be sucked into the black hole. B: If we watch a clock fall toward a black hole, we will see it tick slower and slower as it falls towards the black hole. C: The event horizon of a black hole represents a boundary from which nothing can escape. D: If you watch someone else fall into a black hole, you will never see him or her cross the event horizon. However, he or she will fade from view as the light he or she emits becomes more and more redshifted. E: If you fell into a supermassive black hole (so that you could survive the tidal forces), you would experience time to be running normally as you plunged across the event horizon. A: If the Sun magically disappeared and was replaced by a black hole of the same mass, Earth would soon be sucked into the black hole.
Why does stellar main-sequence lifetime decrease with increasing stellar mass?
A: It doesn't; higher mass stars have more hydrogen available for fusion, and thus have longer lifetimes. B: Strong stellar winds cause higher mass stars to lose mass quickly. C: Higher outward pressure prevents the core hydrogen from being replenished by the star's outer layers. D:Higher core temperatures cause fusion to proceed much more rapidly. D: Higher core temperatures cause fusion to proceed much more rapidly.
What is the ultimate fate of an isolated white dwarf?
A: It will cool down and become a cold black dwarf. B: As gravity overwhelms the electron degeneracy pressure, it will become a neutron star. C: The electron degeneracy pressure slowly overwhelms gravity and the white dwarf evaporates. D: As gravity overwhelms the electron degeneracy pressure, it will explode as a nova. E: As gravity overwhelms the electron degeneracy pressure, it will explode as a supernova. A: It will cool down and become a cold black dwarf.
Which of the following best describes what would happen if a 1.5 solar mass neutron star, with a diameter of a few kilometers, were suddenly to appear in your hometown?
A: It would crash into the Earth, throwing vast amounts of dust into the atmosphere which in turn would cool the Earth. Such a scenario is probably what caused the extinction of the dinosaurs. B: The entire mass of the Earth would end up as a thin layer, about 1 cm thick, over the surface of the neutron star. C: It would rapidly sink to the center of the Earth. D: The combined mass of the Earth and the neutron star would cause the neutron star to collapse into a black hole. E: It would crash through the Earth, creating a large crater, and exit the Earth on the other side. B: The entire mass of the Earth would end up as a thin layer, about 1 cm thick, over the surface of the neutron star.
If the sun's surface cooled, how would its appearance change?
A: It would stay the same. B: It would appear more blue. C: It would appear more red. D: It would become bright white. C: It would appear more red.
Which of the following comparisons between low-mass stars and high-mass main-sequence stars is true?
A: Low-mass stars are hotter but less luminous than high-mass stars. B: Low-mass stars are hotter and more luminous than high-mass stars. C: Low-mass stars are cooler but more luminous than high-mass stars. D: Low-mass stars are cooler and less luminous than high-mass stars. E: Low-mass stars have the same temperature and luminosity as high-mass stars. D: Low-mass stars are cooler and less luminous than high-mass stars.
What are the standard units for luminosity?
A: Newtons B: Joules C: Watts per second D: kilograms E: Watts E: Watts
Which of the following statements is not true about the planets so far discovered around other stars?
A: Photographs reveal that most of them have atmospheres much like that of Jupiter. B: Many of them orbit closer to their star than Jupiter orbits the Sun. C: Many of them have been discovered by observing Doppler shifts in the spectra of the stars they orbit. D: Most of them are more massive than Earth. A: Photographs reveal that most of them have atmospheres much like that of Jupiter.
What causes the radio pulses of a pulsar?
A: The neutron star's orbiting companion periodically eclipses the radio waves that the neutron star emits. B: A black hole near the neutron star absorbs energy and re-emits it as radio waves. C: The vibration of the neutron star D: The neutron star undergoes periodic explosions of nuclear fusion that generate radio pulses. E: As the neutron star spins, beams of radio radiation sweep through space. If one of the beams crosses the Earth, we observe a pulse. E: As the neutron star spins, beams of radio radiation sweep through space. If one of the beams crosses the Earth, we observe a pulse.
Which of the following statements about the sunspot cycle is not true?
A: The number of solar flares peaks about every 11 years. B: The number of sunspots peaks approximately every 11 years. C: The rate of nuclear fusion in the Sun peaks about every 11 years. D: At solar minimum, the first sunspots form at mid-latitudes on the Sun. E: The magnetic polarity of the Sun reverses approximately every 11 years. C: The rate of nuclear fusion in the Sun peaks about every 11 years.
Compared to the star it evolved from, a red giant is
A: hotter and dimmer. B: hotter and brighter. C: cooler and dimmer. D: the same temperature and brightness. E: cooler and brighter. E: cooler and brighter
What would happen to the core of the sun if its temperature rose slightly?
A: The rate at which fusion occurs would decrease, leading to an expansion of the core, which would in turn cause the temperature to drop back down. B: The rate at which fusion occurs would decrease, leading to a contraction of the core, which would in turn cause a further temperature rise. C: The rate at which fusion occurs would increase, leading to an expansion of the core, which would in turn cause the temperature to drop back down. D: The rate at which fusion occurs would increase, leading to a contraction of the core, which would in turn cause the temperature to rise even further. C: The rate at which fusion occurs would increase, leading to an expansion of the core, which would in turn cause the temperature to drop back down.
What is the upper limit to the mass of a white dwarf?
A: There is no upper limit. B: There is an upper limit, but we do not yet know what it is. C: 1.4 solar masses D: 2 solar masses E: 1 solar mass C: 1.4 solar masses
Why do sunspots appear dark?
A: They are thick clouds on the sun, blocking its light. B: They are regions nearly devoid of gas. C: They are regions that are significantly cooler than the rest of the photosphere. D: They are composed of different elements than the rest of the sun. C: They are regions that are significantly cooler than the rest of the photosphere.
What are the standard units for apparent brightness?
A: Watts per second B: Newtons C: Watts per square meter D: Watts E: Joules C: watts per square meter
Why is there an upper limit to the mass of a white dwarf?
A: White dwarfs come only from stars with masses less than 1.4 solar masses. B: The upper limit to the masses of white dwarfs was determined through observations of white dwarfs in binary systems, but no one knows why the limit exists. C: The more massive the white dwarf, the higher its temperature and hence the greater its degeneracy pressure. Near 1.4 solar masses, the temperature becomes so high that all matter effectively melts into subatomic particles. D: The more massive the white dwarf, the greater the degeneracy pressure and the faster the speeds of its electrons. Near 1.4 solar masses, the speeds of the electrons approach the speed of light, and no more mass can be supported. D: The more massive the white dwarf, the greater the degeneracy pressure and the faster the speeds of its electrons. Near 1.4 solar masses, the speeds of the electrons approach the speed of light, so more mass cannot be added without breaking the degeneracy pressure.
A white dwarf is
A: a cool and very small main sequence star with a mass of less than 1.4 of a solar masses. B: the exposed core of a dead star, supported by electron degeneracy pressure. C: a hot but very small main sequence star with a mass of less than 1.4 solar masses. D: the name for the singularity at the center of a black hole. E: the exposed core of a dead star, supported by neutron degeneracy pressure. B: the exposed core of a dead star, supported by electron degeneracy pressure.
Which of the following is closest in size (radius) to a neutron star?
A: a football stadium B: the Sun C: a city D: the Earth E: a basketball C: a city
If you were to come back to our Solar System in 6 billion years, what might you expect to find?
A: a red giant star B: a white dwarf C: a black hole D: a rapidly spinning pulsar E: Everything will be essentially the same as it is now. B: a white dwarf
A teaspoonful of white dwarf material on Earth would weigh
A: about the same as Mt. Everest. B: about the same as the Earth. C: a few pounds. D: a few grams. E: a few tons. E: a few tons
After a massive-star supernova, what is left behind?
A: always a black hole B: always a neutron star C: always a white dwarf D: either a white dwarf or a neutron star E: either a neutron star or a black hole E: either a neutron star or a black hole
The core of the Sun is
A: at the same temperature and density as its surface. B: composed of iron. C: much hotter and much denser than its surface. D: constantly rising to the surface through convection. E: at the same temperature but much denser than its surface. C: much hotter and much denser than its surface.
The first planets around other Sun-like stars were discovered
A: at the turn of this century B: by Huyugens, followinf his realization that other stars are suns C: about 2 decades ago D: by galileo following the invention of the telescope E: at the turn of last century C: about 2 decades ago
Hydrogen fusion in the Sun requires a temperature (in Kelvin) of
A: billions of degrees. B: millions of degrees. C: trillions of degrees. D: thousands of degrees. E: any temperature, as long as gravity is strong enough. B: millions of degrees
Which of the following is not a method astronomers use to determine the physical conditions inside the Sun?
A: building mathematical models that use the laws of physics B:measuring Doppler shifts to observe solar vibrations C: observing X-ray images of the solar interior using satellites D: detecting solar neutrinos generated in the Sun's core E: both C and D C: observing X-ray images of the solar interior using satellites
By what process do nuclear power plants on the Earth generate energy?
A: chemical reactions B: converting kinetic energy into electricity C: converting gravitational potential energy into electricity D: nuclear fission E: nuclear fusion D: nuclear fission
Compared to the star it evolved from, a white dwarf is
A: cooler and brighter. B: cooler and dimmer. C: the same temperature and brightness. D: hotter and brighter. E: hotter and dimmer. E: hotter and dimmer
What kind of pressure supports a white dwarf?
A: electron degeneracy pressure B: radiation pressure C: neutron degeneracy pressure D: thermal pressure E: all of the above A: electron degeneracy pressure
On the main sequence, stars obtain their energy
A: from chemical reactions. B: by converting helium to carbon, nitrogen, and oxygen. C: from gravitational contraction. D: from nuclear fission. E: by converting hydrogen to helium. E: by converting hydrogen to helium
Which planet search technique is currently best suited to finding Earth-like planets?
A: gravitational lensing B: Doppler C: astrometric D: transit E: combining all the above D: in transit
Which of the following best describes the axes of a Hertzsprung-Russell (H-R) diagram?
A: interior temperature on the horizontal axis and mass on the vertical axis B: surface temperature on the horizontal axis and radius on the vertical axis C: mass on the horizontal axis and stellar age on the vertical axis D: surface temperature on the horizontal axis and luminosity on the vertical axis E: mass on the horizontal axis and luminosity on the vertical axis D: surface temperature on the horizontal axis and luminosity on the vertical axis
If the distance between us and a star is doubled, with everything else remaining the same, its luminosity
A: is decreased by a factor of four, but its apparent brightness remains the same. B: is decreased by a factor of two, and its apparent brightness is decreased by a factor of two. C: remains the same, but its apparent brightness is decreased by a factor of two. D: is decreased by a factor of four, and its apparent brightness is decreased by a factor of four. E: remains the same, but its apparent brightness is decreased by a factor of four. E: remains the same, but its apparent brightness is decreased by a factor of four.
Which of the following is the phase of matter in the Sun?
A: liquid B: gas C: solid D:plasma E: a mixture of all of the above D: plasma
Which of the following correctly states the relationship between the apparent brightness, luminosity, and distance of a star?
A: luminosity = apparent brightness/ 4pi x (distance)^2 B: distance = luminosity/4pi x (apparent brightness)^2 C: apparent brightness = luminosity/4pi x (distance)^2 D: apparent brightness = luminosity x 4π x (distance)^2 C: Apparent brightness = luminosity/4pi x (distance)^2
Since all stars begin their lives with the same basic composition, what characteristic most determines how they will differ?
A: luminosity they are formed with B: time they are formed C: color they are formed with D: location where they are formed E: mass they are formed with E: mass they are formed with
The Doppler technique can be used to estimate the semimajor axis of a planet's orbit by
A: measuring the time it takes for the star's line-of-sight velocity to cycle from peak to peak, and using Newton's version of Kepler's Third law. B: measuring the amount by which the starlight is reduced when the planet transits. C: measuring the speed at which the star orbits the mutual center-of-mass of the star and planet, and using Newton's theory of gravity. D: measuring the asymmetries in the velocity curve. A: measuring the time it takes for the star's line-of-sight velocity to cycle from peak to peak, and using Newton's version of Kepler's Third law.
The Doppler technique can be used to measure the orbital period of a planet by
A: measuring the time it takes for the star's line-of-sight velocity to cycle from peak to peak. B: measuring the amount by which the starlight is reduced when the planet transits. C: measuring the asymmetries in the velocity curve. D: measuring the speed at which the star orbits the mutual center-of-mass of the star and planet. A: measuring the time it takes for the star's line-of-sight velocity to cycle from peak to peak
Based on its surface temperature of 6,000 K, most photons that leave the Sun's surface lie in which region of the electromagnetic spectrum?
A: microwave B: X-ray C: ultraviolet D: infrared E: visible E: visible
The reason that most extrasolar planets discovered by the transit technique are found close to their parent stars is
A: more of the starlight is blocked by the planet when it transits the star. B: they transit more frequently, and have thus been more likely to be detected in the short time we have been searching for them. C: the closer to a star, the hotter and therefore brighter the planet is. D: planets that are close to a star are heated up and therefore larger. E: the wavelength shift of the star's spectrum is larger. B: they transit more frequently, and have thus been more likely to be detected in the short time we have been searching for them.
A paperclip with the density of a neutron star would weigh (on the Earth)
A: more than Mt. Everest. B: about the same as a regular paperclip. C: more than the Earth. D: a few tons. E: more than the Moon. A: more than Mt. Everest.
What keeps the Sun's outer layers from continuing to fall inward in a gravitational collapse?
A: neutrinos produced by nuclear fusion drag gas outward B: electromagnetic repulsion between protons C: the strong force between protons D: outward pressure due to super-heated gas D: outward pressure due to super-heated gas
By what process does the Sun generate energy?
A: nuclear fusion B: gravitational contraction C: nuclear fission D: gradual expansion E: chemical reactions A: nuclear fusion
At the center of the Sun, nuclear fusion converts hydrogen into
A: radiation and elements such as carbon and nitrogen. B: radioactive elements such as uranium and plutonium. C: helium, gamma rays, and neutrinos. D: molecular hydrogen. E: hydrogen compounds such as methane. C: helium, gamma rays, and neutrinos.
The light radiated from the Sun's surface reaches Earth in about 8 minutes. However, the energy of this light was released by fusion in the Sun's core about
A: several thousand years ago. B: 11 years ago. C: several hundred thousand years ago. D: several hundred years ago. E: 8 minutes ago. C: several hundred thousand years ago.
What types of stars end their lives with supernovae?
A: stars that are at least several times the mass of the Sun B: all stars that are red in color C: all stars that are yellow in color D: stars that are similar in mass to the Sun E: stars that have reached an age of 10 billion years A: stars that are at least several times the mass of the Sun
The spectral sequence sorts stars according to
A: surface temperature. B: radius. C: mass. D: core temperature. E: luminosity A: surface temperature
Approximately how many other planetary systems have been discovered to date?
A: tens of thousands B: about 2 hundred C: about 2 thousand D: ten E: millions C about 2 thousand
What did Carl Sagan mean when he said that we are all "star stuff"?
A: that the Earth formed at the same time as the Sun B: that the universe contains billions of stars C: that the Sun formed from the interstellar medium: the "stuff" between the stars D: that life would be impossible without energy from the Sun E: that the carbon, oxygen, and other elements essential to life were created by nucleosynthesis in stellar cores E: that the carbon, oxygen, and other elements essential to life were created by nucleosynthesis in stellar cores
Which of the following is closest in size (radius) to a white dwarf?
A: the Earth B: a basketball C: a football stadium D: the Sun E: a small city A: the earth
Which of the following is closest in mass to a white dwarf?
A: the Earth B: the Moon C: the Sun D: Jupiter C: the sun
What eventually halts the gravitational collapse of an interstellar gas cloud that forms an object that is massive enough to become a star?
A: the central object becoming hot enough to sustain nuclear fusion in its core B: a critical fraction of the gas has been driven further into space C: the crowding of electrons in the core D: nothing; all collapsing gas clouds become black holes A: the central object becoming hot enough to sustain nuclear fusion in its core
The depth of the dip in a star's brightness due to the transit of a planet depends most directly on
A: the size of the planet's orbit. B: the eccentricity of the planet's orbit. C: the planet's mass. D: the planet's size. E: the planet's density. D: the planet's size
Which of the following processes is involved in the sunspot cycle?
A: the winding of magnetic field lines due to the Sun's rotation B: a large change in the amount of visible light emitted by the Sun C: small variations in the rate of nuclear energy generation in the solar interior D: a slight gravitational contraction of the Sun E: an imbalance in the operation of the solar thermostat A: The winding of magnetic field lines due to the Sun's rotation
No stars are expected with masses greater than 150 times our Sun because
A: they would be too massive for hydrogen fusion to occur in their cores. B: they would shine exclusively at X-ray wavelengths and would be difficult to detect. C: molecular clouds do not have enough material to form such massive stars. D: they would fragment into binary stars because of their rapid rotation. E: they would generate so much power that they would blow themselves apart. E: they would generate so much power that they would blow themselves apart.
A star's luminosity is the
A: total amount of energy that the star will radiate over its entire lifetime. B: surface temperature of the star. C: lifetime of the star. D: total amount of energy that the star radiates each second. E: apparent brightness of the star in our sky. D: total amount of light that the star radiates each second
On a Hertzsprung-Russell diagram, where would you find stars that are cool and luminous?
A: upper right B: lower right C: upper left D: lower left A: upper right
On a Hertzsprung-Russell diagram, where would you find red giant stars?
A: upper right B: lower right C: upper left D: lower left A: upper right
On a Hertzsprung-Russell diagram, where would you find stars that have the largest radii?
A: upper right B: lower right C: upper left D: lower left A: upper right
On a Hertzsprung-Russell diagram, where would you find stars that are cool and dim?
A: upper right B: lower right C: upper left D: lower left B: lower right
On a Hertzsprung-Russell diagram, where on the main sequence would you find stars that have the greatest mass?
A: upper right B: lower right C: upper left D: lower left C: upper left
On a Hertzsprung-Russell diagram, where would you find white dwarfs?
A: upper right B: lower right C: upper left D: lower left D: lower left
What can we learn about a star from a life track on an H-R diagram?
A: what surface temperature and luminosity it will have at each stage of its life B: how long ago it was born C: where it is located D: when it will die E: all of the above A: what surface temperature and luminosity it will have at each stage of its life
Which of the following sequences correctly describes the stages of life for a low-mass star?
A: white dwarf, main-sequence, red giant, protostar B: protostar, main-sequence, red giant, white dwarf C: red giant, protostar, main-sequence, white dwarf D: protostar, main-sequence, white dwarf, red giant E: protostar, red giant, main-sequence, white dwarf B: protostar, main-sequence, red giant, white dwarf
When does a star become a main-sequence star?
A:when a star becomes luminous enough to emit thermal radiation B: when hydrogen fusion is occurring throughout the star's interior C: when the protostar assembles from its parent molecular cloud D: the instant when hydrogen fusion first begins in the star's core E: when the rate of hydrogen fusion in the star's core is high enough to sustain gravitational equilibrium E: when the rate of hydrogen fusion in the star's core is high enough to sustain gravitational equilibrium
It is impossible for a star to have a negative apparent magnitude, such as -1. T/F
False
Most of the planets discovered around other stars have masses comparable to the terrestrial planets in our own solar system. T/F
False
Our Sun will likely undergo a nova event in about 5 billion years. T/F
False
The apparent brightness of a star depends only on its luminosity. T/F
False
The heaviest element produced by stars or in supernovae is silicon. T/F
False
There is no limit to the mass with which a star can be born. T/F
False
There is no upper limit to the mass of a neutron star. T/F
False
We can measure the parallax of most stars in our galaxy. T/F
False
A planet's size can be determined by observing its transit across a star. T/F
True
A star with an apparent magnitude of 10 appears fainter than a star with an apparent magnitude of 9. T/F
True
In any star cluster, stars with lower masses greatly outnumber those with higher masses. T/F
True
The faintest visible stars to the naked eye have an apparent magnitude of about 6. T/F
True
The more distant a star, the smaller its parallax. T/F
True
The proton-proton chain converts four hydrogen nuclei into one helium nucleus plus energy. T/F
True
The sun rotates more quickly at the equator than at the poles. T/F
True