Exam 3 Study Guide

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 rapidly spinning pulsar C) a white dwarf D) a black hole E) Everything will be essentially the same as it is now.

Suppose you drop a clock toward a black hole. As you look at the clock from a high orbit, what will you notice? A) The clock will fall faster and faster, exceeding the speed of light as it crosses the event horizon. B) Time on the clock will run faster as it approaches the black hole, and light from the clock will be increasingly blueshifted. C) The clock will fall toward the black hole at a steady rate, so that you'll see it plunge through the event horizon within just a few minutes. D) Time on the clock will run slower as it approaches the black hole, and light from the clock will be increasingly redshifted.

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 fall into the black hole. B) If you watch an object fall into a black hole, you will never see the object cross the event horizon. However, the object will fade from view as the light it emits becomes more and more redshifted. C) The event horizon of a black hole represents a boundary from which nothing can escape. D) 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. E) If we watch a clock fall toward a black hole, we will see it tick slower and slower.

Which of the following correctly describes how light will be affected as it tries to escape from a massive object like a neutron star? A) The light will be blueshifted. B) The light will be redshifted. C) Light doesn't have mass; therefore, it is not affected by gravity. D) The visible light will be redshifted, but higher frequencies, such as X-rays and gamma rays, will not be affected.

What causes the radio pulses of a pulsar? A) The neutron star undergoes periodic explosions of nuclear fusion that generate radio pulses. B) As the neutron star spins, beams of radio radiation sweep through space. If one of the beams crosses the Earth, we observe a pulse. C) The vibration of the neutron star. D) The neutron star's orbiting companion periodically eclipses the radio waves that the neutron star emits. E) A black hole near the neutron star absorbs energy and re-emits it as radio waves.

Which of the following is closest in size (radius) to a neutron star? A) a city B) the Sun C) a basketball D) the Earth E) a football stadium

After a massive-star supernova, what is left behind? A) always a neutron star B) always a white dwarf C) always a black hole D) either a white dwarf or a neutron star E) either a neutron star or a black hole

Which of the following is closest in size (radius) to a white dwarf? A) a small city B) the Sun C) a football stadium D) a basketball E) the Earth

What kind of pressure supports a white dwarf? A) electron degeneracy pressure B) thermal pressure C) neutron degeneracy pressure D) radiation pressure E) all of the above

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) The white dwarf undergoes a collapse and expels the excess mass in a nova eruption. B) Temperatures skyrocket to the point where carbon fusion is possible, which leads to a white dwarf supernova explosion. C) 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. D) The white dwarf immediately collapses into a black hole, disappearing from view.

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) 2 solar masses D) 1 solar mass E) 1.4 solar masses

What kind of pressure supports a neutron star? A) electron degeneracy pressure B) neutron degeneracy pressure C) radiation pressure D) thermal pressure E) all of the above

) Which of the following statements about the stages of nuclear burning in a massive star iscnot true? A) Each successive stage lasts for approximately as long as the first, hydrogen fusion stage. B) As each stage ends, the core shrinks further. C) Each successive stage of fusion requires higher temperatures than the previous stages. D) Each successive stage creates an element with a higher atomic mass.

What types of stars end their lives with supernovae? A) stars that are more massive than eight times the mass of the Sun B) all stars that are yellow in color C) all stars that are red in color D) stars that have reached an age of 10 billion years E) stars that are similar in mass to the Sun

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.

What is the CNO cycle? A) the period of a massive star's life when carbon, nitrogen, and oxygen are fusing in different shells outside the core B) the process by which carbon is fused into nitrogen and oxygen C) the process by which helium is fused into carbon, nitrogen, and oxygen D) a type of hydrogen fusion that uses carbon, nitrogen, and oxygen atoms as catalysts E) the period of a low-mass star's life when it can no longer fuse carbon, nitrogen, and oxygen in its core

Which of the following sequences correctly describes the stages of life for a one solar mass star? A) protostar, main-sequence, red giant, white dwarf B) protostar, main-sequence, white dwarf, red giant C) protostar, red giant, main-sequence, white dwarf D) red giant, protostar, main-sequence, white dwarf E) white dwarf, main-sequence, red giant, protostar

What is a planetary nebula? A) the expanding shell of gas that is no longer gravitationally bound to the core of a star B) the molecular cloud from which planets form C) what is left of its planets after a low-mass star has ended its life D) the expanding shell of gas that is left when a white dwarf explodes as a supernova E) a disk of gas surrounding a protostar that may form into planets

How many helium nuclei fuse together to make a carbon nucleus? A) 2 B) 3 C) 4 D) It varies depending on the reaction. E) Helium cannot fuse into carbon.

What percentage of a star's total lifetime is spent on the main sequence? A) 10% B) 20% C) 50% D) 90% E) 100%

What eventually halts the gravitational collapse of an interstellar gas cloud if it 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) nothing; all collapsing gas clouds become black holes D) the crowding of electrons in the core

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 life would be impossible without energy from the Sun C) that the Sun formed from the interstellar medium: the "stuff" between the stars D) that the carbon, oxygen, and other elements essential to life were created by nucleosynthesis in stellar cores E) that the universe contains billions of stars

What is the approximate surface temperature of a B star? A) 40,000 K B) 6,000 K C) 20,000 K D) 8,000 K

The brightest main-sequence star in a cluster has a temperature of 10,000 K and a luminosity about 10 times greater than the sun. What is the approximate age of the cluster? A) About 1011 years B) About 109 years C) About 107 years D) This cannot be answered using the HR diagram.

Which of the following comparisons between low-mass stars and high-mass main-sequence stars is true? A) Low-mass stars have the same temperature and luminosity as high-mass stars. B) Low-mass stars are cooler but more luminous than high-mass stars. C) Low-mass stars are hotter but less luminous than high-mass stars. D) Low-mass stars are hotter and more luminous than high-mass stars. E) Low-mass stars are cooler and less luminous than high-mass stars.

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.

On a Hertzsprung-Russell diagram, where would you find red giant stars? A) upper right B) lower right C) upper left D) lower left

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 luminosity on the vertical axis C) mass on the horizontal axis and luminosity on the vertical axis D) surface temperature on the horizontal axis and radius on the vertical axis E) mass on the horizontal axis and stellar age on the vertical axis

You measure the parallax angle for a star to be 0.1 arcseconds. The distance to this star is A) 0.1 parsec. B) 0.1 light-year. C) 10 parsecs. D) 10 light-years. E) impossible to determine.

Which of the following statements about apparent and absolute magnitudes is true? A) The absolute magnitude of a star is dependent upon its luminosity. B) A star with an apparent magnitude of 1 appears brighter than a star with an apparent magnitude of 2. C) A star's absolute magnitude is the apparent magnitude it would have if it were at a distance of 10 parsecs from Earth. D) The magnitude system that we use now is based on a system used by the ancient Greeks over 2,000 years ago that classified stars by how bright they appeared. E) All of the above are true.

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 four. 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 two.

Since all stars begin their lives with the same basic composition, what characteristic is most important in determining how they will differ? A) the time at which they formed B) their initial luminosity C) their initial mass D) their location in the galaxy E) their initial color

Why does the Sun emit neutrinos? A) Convection releases neutrinos, which random walk through the radiation zone. B) The Sun does not emit neutrinos. C) Solar flares create neutrinos with magnetic fields. D) Fusion in the Sun's core creates neutrinos as a byproduct.

What observations characterize solar maximum? A) The Sun becomes much brighter. B) There are many sunspots visible on the surface of the Sun. C) The Sun emits light of longer average wavelength. D) The Sun rotates faster at its poles. E) all of the above

Why do sunspots appear dark? A) They are regions that are significantly cooler than the rest of the photosphere B) They are regions nearly devoid of gas C) The Sun emits light of longer average wavelength D) The Sun rotates faster at its poles E) all of the above

What is the solution to the solar neutrino problem? A) Not all fusion reactions create neutrinos. B) The electron neutrinos created in the Sun's core change into another type of neutrino that we did not originally detect. C) We did not know how to detect neutrinos. D) The Sun is generating energy other than by nuclear fusion. E) The Sun is generating much less energy than we think it is.

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 increase, leading to an expansion of the core, which would in turn cause the temperature to drop back down. C) 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. D) The rate at which fusion occurs would decrease, leading to a contraction of the core, which would in turn cause the temperature to rise even further.

At the center of the Sun, nuclear fusion converts hydrogen into A) helium, gamma rays, and neutrinos. B) molecular hydrogen. C) radioactive elements such as uranium and plutonium. D) radiation and elements such as carbon and nitrogen. E) hydrogen compounds such as methane.

By what process do nuclear power plants on the Earth generate energy? A) nuclear fusion B) converting gravitational potential energy into electricity C) nuclear fission D) converting kinetic energy into electricity E) chemical reactions

The core of the Sun is A) composed of iron. B) at the same temperature and density as its surface. C) at the same temperature but much denser than its surface. D) much hotter and much denser than its surface. E) constantly rising to the surface through convection.

Which theory of physics correctly describes what happens at the singularity of a black hole? A) Special Relativity B) Quantum Mechanics C) General Relativity D) String Theory E) None of the above

The most famous equation of all time is E= mc2 from Albert Einstein's Special Theory of Relativity. What does it mean? A) nuclear weapons are possible B) space and time are relative C) the speed of light is same for all observers D) energy and mass are the same thing E) space and time are the same thing

In Albert Einstein's General Theory of Relativity, the gravity between the Sun and the Earth is A) caused by the relativity of the speed of light. B) caused by the energy contained in the mass of the Sun according to E= mc2. C) the Earth moving in the curved space created by the Sun's mass. D) a force of attraction between the Earth and the Sun that is proportional to the product of their masses. E) a force of attraction between the Earth and the Sun that decreases as 1/r2.

Most of the computers at the Harvard Observatory in the late 19th and early 20th century were A) women astronomers B) mechanical computing machines C) early versions of today's electronic computers D) mathematicians who could perform lengthy calculations very quickly.

Neil deGrasse Tyson has a word for what happens to someone who falls into a blackhole. The word is A) spaghettification B) tidalization C) pizzafication D) singularization E) macraronization

Where did Albert Einstein spend the last two decades of his life? A) Berlin, Germany B) Princeton , New Jersey C) Zurich, Switzerland D) Los Angeles, California E) Boston, Massachusetts

How many children did Albert Einstein have? A) 0 B) 1 C) 2 D) 3 E) 4

What is the only force that can overcome the repulsion between two positively charged nuclei and bind them together? A) the weak force B) the Coriolis force C) the strong force D) the electromagnetic force E) the gravitational force

Who won the Nobel Prize for Physics for the discovery of Pulsars? A) Antony Hewish B) Jocelyn Bell C) Antony Hewish and Jocelyn Bell D) Stephen Hawking E) John Wheeler

Approximately how many neutrinos pass through your body each second? A) about one hundred B) about a thousand trillion C) about one thousand D) None; they are blocked by the Earth's atmosphere.