ASTR quizzes
If you have a 100-watt light bulb, how much energy does it use each hour? A) 360,000 joules B) 3600 watts C) 6,000 watts D) 3600 joules E) 6,000 joules
A) 360,000 joules
If we observed a supernova, how might we tell if it is a white dwarf supernova or a core collapse supernova? A) A white dwarf supernova leaves nothing behind while a massive star supernova leaves behind a black hole or neutron star. B) A white dwarf supernova produces a white hole while a massive star supernova produces a black hole. C) A white dwarf supernova is much less luminous than a massive star supernova. D) A white dwarf supernova has a much longer duration than a massive star supernova
A) A white dwarf supernova leaves nothing behind while a massive star supernova leaves behind a black hole or neutron star.
Relativity of simultaneity implies that: A) Different observers can disagree on the order in which events at different locations occur. B) Different observers must always agree on the order in which all events happen, but can disagree on whether they happen at the exact same time. C) Different observers must agree on whether events are simultaneous, but can disagree on the time interval between non-simultaneous events. D) Different observers must agree on the time interval between events, even if they are simultaneous
A) Different observers can disagree on the order in which events at different locations occur.
How do we infer the spin of black holes in X-ray binaries? A) Fitting the accretion disk emission spectrum with a model. B) Fitting the companion star's emission spectrum with a model. C) Measuring the Doppler shift and period of the companion star. D) By examining the size of jets in radio images of the X-ray binary.
A) Fitting the accretion disk emission spectrum with a model.
How luminous (in gravitational waves) was the first black hole merger detected by LIGO at its peak? A) It was comparable to the luminosity of all the stars in the observable universe. B) It was comparable to the luminosity of the Sun. C) It was comparable to the luminosity of the entire Milky Way galaxy. D) It was comparable to the luminosity of a white dwarf supernova.
A) It was comparable to the luminosity of all the stars in the observable universe.
If the surface temperature of the Sun drops by a factor of two while its radius stays fixed, how would the Sun's luminosity change? A) It would decrease by a factor of 16. B) It would decrease by a factor of 4. C) It would decrease by a factor of 2. D) It would remain the same. E) It would increase by a factor of 2
A) It would decrease by a factor of 16.
A star is moving directly towards Earth. How will the star appear different from an identical star at the same distance that is not moving relative to Earth? A) Its light will be blueshifted. B) Its light will be redshifted. C) It will appear dimmer. D) No difference in appearance is expected.
A) Its light will be blueshifted.
What must happen as the mass of a white dwarf decreases? A) Its radius increases. B) Its radius decreases. C) Its temperature increases. D) Its temperature decreases.
A) Its radius increases.
Gary and Lijun are astronauts exploring an extrasolar planet. Gary lands on the planets surface while Lijun orbits in the command module. The lander and command module are each equipped with an atomic clock to tell time. What do Gary and Lijun perceive about each other's clocks? A) Lijun thinks that Gary's clock is slow while Gary thinks that Lijun's clock is fast. B) Gary thinks that Lijun's clock is slow while Lijun thinks that Gary's clock is fast. C) Both think that the other's clock is slow. D) Both think that the other's clock is fast.
A) Lijun thinks that Gary's clock is slow while Gary thinks that Lijun's clock is fast.
Gary and Lijun are astronauts exploring an extrasolar planet. Gary lands on the planets surface while Lijun orbits in the command module. Gary and Lijun communicate via radio waves. What do the perceive about the radio waves that they send each other? A) Lijun thinks that Gary's radio waves are redshifted while Gary thinks that Lijun's radio waves are blueshifted. B) Gary thinks that Lijun's radio waves are redshifted while Lijun thinks that Gary's radio waves are blueshifted. C) Both think that the other's radio waves are blueshifted. D) Both think that the other's radio waves are redshifted.
A) Lijun thinks that Gary's radio waves are redshifted while Gary thinks that Lijun's radio waves are blueshifted.
Which government agency provides the most funding for astronomy in the U.S.A.? A) National Aeronautics and Space Administration B) National Science Foundation C) Department of Energy D) United Federation of Planets
A) National Aeronautics and Space Administration
What is the cosmic censorship hypothesis? A) Singularities are always hidden behind event horizons. B) We cannot know what happens inside an event horizon because no information (light) can leave the black hole. C) Any information about matter falling into the black hole is lost to the outside universe. D) Black holes are determined by only three parameters. E) Singularities are forbidden from forming when a star collapses
A) Singularities are always hidden behind event horizons.
What was the strongest evidence for gravitational waves prior to direct detection with LIGO? A) The small changes in orbital period observed in some neutron star binaries. B) The tendency of individual neutron stars to spin down as they age. C) Constraints from the cosmic microwave background. D) The absence of any observable binaries with two black holes.
A) The small changes in orbital period observed in some neutron star binaries.
What mechanism is thought to power the radio emission in black hole X-ray binaries and quasars? A) The twisting of magnetic field lines by a spinning black hole. B) The thermal emission from a black hole accretion disk. C) The merger of two black holes in a binary. D) Hawking radiation.
A) The twisting of magnetic field lines by a spinning black hole.
What does the gas in an accretion disk need to lose in order to accrete onto the black hole? A) angular momentum. B) entropy. C) kinetic energy. D) velocity.
A) angular momentum.
You and a highway patrolman are driving at constant speeds in opposite directions on a straight highway. The patrolman is driving at 90 mph and his radar gun determines your relative speed (the magnitude of the difference between your velocities) to be 100 mph. What is your speed at the time of measurement? A) 190 mph B) 10 mph C) 90 mph D) 125 mph
B) 10 mph
According to the equivalence principle, which of the following observers is equivalent to an inertial observer who experiences no acceleration? A) Any non-inertial observer. B) A freely falling observer. C) An observer who is static in a gravitational field. D) An observer who is being accelerated by gravity as well as other forces simultaneously.
B) A freely falling observer.
What does the "no hair" theorem imply about black holes? A) Black holes are characterized by hundreds of parameters. B) Black holes are uniquely specified by knowing their angular momentum (spin), charge, and mass. C) All black holes have the same angular momentum (spin), charge, and mass. D) No two black holes can have the same angular momentum (spin), charge, and mass.
B) Black holes are uniquely specified by knowing their angular momentum (spin), charge, and mass.
If the efficiency of black hole accretion is 0.1 and the efficiency of nuclear fusion is 0.007, how much more or less mass does one need to power a source using nuclear power rather than black hole accretion? A) Fusion requires about 70 times more mass. B) Fusion requires about 14 times more mass. C) Fusion requires about 7 times more mass. D) Fusion requires about 7 times less mass.
B) Fusion requires about 14 times more mass.
Which of the following is a true statement about geodesics? A) Photons must follow geodesics but massive particles cannot. B) Geodesics are the shortest distance between two points in curved space time. C) Particles following geodesics must experience forces other than gravity D) All of the above. E) A and B.
B) Geodesics are the shortest distance between two points in curved space time.
Can a particle that has non-zero rest mass (equal to m) ever reach the speed of light? A) No, because a massive particle traveling at the speed of light would have energy 1/2mc2 which is more than its rest mass energy. B) No, because a massive particle traveling at the speed of light would have infinite energy and would therefore require an infinite amount of energy to accelerate. C) Yes. You just need to give it an amount of energy equal to mc2 . D) Yes, but it will require a much larger amount of energy than mc2 .
B) No, because a massive particle traveling at the speed of light would have infinite energy and would therefore require an infinite amount of energy to accelerate.
What was the primary motivation for LIGO to build two detectors separated by 3000 km? A) The separation distance is not important but they built two detectors primarily to increase their sensitivity. B) So that local sources of noise that mimic gravitational waves could be ruled out if they showed up in only one detector. C) The wavelength of the gravitational waves that they wanted to detect were about ∼ 3000 km. D) One detector can always be kept on when the other one is shut down for maintenance and upgrades.
B) So that local sources of noise that mimic gravitational waves could be ruled out if they showed up in only one detector.
What do physicists mean when they say that energy is conserved? A) The energy of a closed system can go up or stay the same, but never decrease. B) The forms of energy in a closed system can change, but the sum of all forms of energy must remain the same. C) The forms of energy of a closed system can change, but the sum of all forms of energy can only decrease or remain the same. D) The forms of energy in a closed system must remain the same.
B) The forms of energy in a closed system can change, but the sum of all forms of energy must remain the same.
Why do black hole X-ray binaries emit most of their energy at X-ray wavelengths? A) The luminosity is small and the emitting area is small. B) The luminosity is large and the emitting area is small. C) The luminosity is small and the emitting area is large. D) The luminosity is large and the emitting area is large.
B) The luminosity is large and the emitting area is small.
Which of the following is true on the surface of a sphere? A) The sum of angles in a triangle is less than 180◦ . B) The sum of angles in triangle is greater than 180◦ . C) The shortest distance between two points is a straight line. D) The circumference of a circle is greater than 2πR, where R is the radius of the circle
B) The sum of angles in triangle is greater than 180◦ .
Tina weighs 60 kg and is traveling 2 m/s while Doug weighs 120 kg and is traveling at 1 m/s. How do their kinetic energies compare? A) Tina's kinetic energy is half Doug's kinetic energy. B) Tina's kinetic energy is double Doug's kinetic energy. C) Tina's kinetic energy is quadruple Doug's kinetic energy. D) Tina's kinetic energy is one-fourth Doug's kinetic energy. E) Their kinetic energies are equal.
B) Tina's kinetic energy is double Doug's kinetic energy.
In which case does the astronaut have the largest gravitational potential energy relative to the Earth? A) standing at sea level. B) floating in deep space far from Earth. C) flying in an airplane. D) floating on the space station in low Earth orbit
B) floating in deep space far from Earth
Imagine your insane physicist friend gives you 5 micrograms (5×10−6 kg) of antimatter as a surprise birthday present. As you open the special containment box it came in, it immediately comes into contact with normal matter and annihilates. How much energy is released? (Hint: Remember that there is a factor of 2 because the rest mass energy of the matter it annihilates with also contributes. This would almost certainly kill you.) A) 3 joules B) 9 × 105 joules C) 9 × 1011 joules D) 9 × 1014 joules
C) 9 × 1011 joules
Which of the following would be the strongest source of gravitational waves? A) A spinning black hole. B) A spinning neutron star. C) A neutron star binary close to merger. D) A binary with two main sequence stars.
C) A neutron star binary close to merger.
Sanjay and Delia are two astronauts traveling in opposite directions with a relative speed of 0.99 c. Which of the following is true? A) Sanjay thinks that Delia's mass increases, Delia thinks that Sanjay's mass decreases. B) Delia thinks that Sanjay's mass increases, Sanjay thinks that Delia's mass decreases. C) Both think that the other's mass increases. D) Both think that the other's mass decreases.
C) Both think that the other's mass increases.
In which of the following cases is a person experiencing a net force? A) Standing on the Earth. B) Moving in a car at constant velocity. C) Falling from an airplane. D) Moving in a boat at constant velocity.
C) Falling from an airplane.
Dong and Ellie are astronauts traveling in spaceships with a relative speed of 0.8 c. What does Dong perceive about Ellie? A) Her length is contracted and her clock runs fast. B) Her length is normal and her clock runs fast. C) Her length is contracted and her clock runs slow. D) Her length is increased and her clock runs slow. E) Her length is increased and her clock runs fast
C) Her length is contracted and her clock runs slow.
What is meant by the term spaghettification? A) If you fall into a black hole, tidal forces will compress your body in the radial direction. B) If you fall into a black hole, tidal forces will stretch your body in the radial direction, but leave it unchanged in the perpendicular direction. C) If you fall into a black hole, tidal forces will stretch your body in the radial direction and compress it in the perpendicular direction. D) The frame dragging effect twists your body as you fall into a black hole, stretching you and winding you up like spaghetti.
C) If you fall into a black hole, tidal forces will stretch your body in the radial direction and compress it in the perpendicular direction.
What is the most accurate method that we use to infer the mass of black holes in X-ray binaries? A) Fitting the accretion disk emission spectrum with a model. B) Measuring the Doppler shift and period of the black hole's motion directly. C) Measuring the Doppler shift and period of the companion star. D) Fitting the time variability of the accretion disk emission.
C) Measuring the Doppler shift and period of the companion star.
Why does an iron core represent the end of thermal pressure support in a high mass star? A) The core becomes so hot that neutron degeneracy pressure overwhelms thermal pressure. B) Nuclear fission takes over as the main energy source, but is unstable and explodes the star as a supernova. C) Nuclear fusion ceases to be an energy source, so the core cools and loses thermal pressure support. D) Once the core becomes iron, its gravitational attraction becomes so strong that no amount of thermal pressure support can balance it.
C) Nuclear fusion ceases to be an energy source, so the core cools and loses thermal pressure support.
Which of the following is the shortest length? A) Schwarzschild radius of the Sun. B) Schwarzschild radius of Earth. C) Schwarzschild radius of the Moon. D) Schwarzschild radius of Jupiter.
C) Schwarzschild radius of the Moon.
What happens to the color of objects if you fall freely into a black hole? A) Everything is blueshifted. B) Everything is redshifted. C) Some objects appear blueshifted and some appear redshifted, depending on which direction you look. D) All objects have their "normal" color, but their images appear distorted due to gravitational lensing. E) Everything appears black because light is trapped.
C) Some objects appear blueshifted and some appear redshifted, depending on which direction you look.
Which of the following statements about the innermost stable circular orbit (ISCO) of a black hole is correct? A) Orbits at radii smaller than the ISCO radius are stable, while those farther from the black hole are unstable. B) The ISCO for any black hole is always at three Schwarzschild radii. C) The location of the ISCO radius depends on the black hole's angular momentum. D) Photons can orbit at the ISCO radius.
C) The location of the ISCO radius depends on the black hole's angular momentum.
Which of the following is a true statement about black holes? A) The mass of a black hole can increase, but can never decrease. B) The mass of a non-spinning black hole can be reduced via the Penrose process. C) The mass of a spinning black hole can be reduced via the Penrose process. D) The mass of a charged black hole can be reduced via the Penrose process.
C) The mass of a spinning black hole can be reduced via the Penrose process.
Why are there usually two low tides per day at any location on the Earth? A) One low tide is caused by the Moon's gravity and a second low tide is caused by the Sun's gravity. B) The tidal bulges are both toward and opposite the Moon's location and these bulges move across the Earth's surface as the Moon orbits the Earth. C) The tidal bulges are both toward and opposite the Moon's location and the Earth's surface moves relative to the bulges as Earth rotates. D) Low tides are simply the times when the Earth's oceans return to the level they would be at if the Moon's gravity were not present and this happens twice per day.
C) The tidal bulges are both toward and opposite the Moon's location and the Earth's surface moves relative to the bulges as Earth rotates
What makes pulsars so useful to astronomers? A) They are very bright and all have the same luminosity so we can use them to measure distances to other galaxies. B) The absorption lines in their spectra allow us to make sensitive tests of general relativity in regions of strong gravity. C) Their large inertia and rapid spins make their pulses very precise clocks. D) We can measure their ages very accurately, putting lower limits on the age of the universe
C) Their large inertia and rapid spins make their pulses very precise clocks.
Why do high mass stars have shorter main-sequence lifetimes than lower mass stars? A) They have less hydrogen to fuse to helium. B) They have less helium to fuse to higher atomic number elements. C) Their luminosities are much larger than lower mass stars. D) When fusing hydrogen, massive stars are less stable than low mass stars.
C) Their luminosities are much larger than lower mass stars.
Which of the following is implied by frame dragging in general relativity? A) Just outside a black hole, frame dragging will rip apart the atoms in your body into the individual protons, neutrons and electrons. B) All orbits are unstable. C) There are no static observers inside a spinning black hole's ergosphere. D) All of the above. E) Only B and C.
C) There are no static observers inside a spinning black hole's ergosphere.
What was the purpose of the Michelson-Morley experiment? A) They were checking to see if the theory of special relativity was correct. B) They were trying to use the known speed of light to measure the Earth's velocity. C) They were trying to measure the expected change in the speed of light relative to Earth's motion. D) They were trying to show that the speed of light was constant.
C) They were trying to measure the expected change in the speed of light relative to Earth's motion.
In order for the global positioning system to work properly, engineers must account for which of the following? A) Gravitational time dilation only. B) Time dilation due to the satellites motion only. C) Time dilation due to both gravity and the satellite's motion. D) None of the above.
C) Time dilation due to both gravity and the satellite's motion.
If the beam of radio emission from as spinning neutron star hit the Earth: A) We would all die. B) We would call it a collapsar. C) We would call it a pulsar. D) We would call it a quasar.
C) We would call it a pulsar.
From lowest frequency to highest frequency, which of the following correctly order the different categories of electromagnetic radiation? A) radio, X-rays, visible light, ultraviolet, infrared, gamma rays B) gamma rays, X-rays, visible light, ultraviolet, infrared, radio C) radio, infrared, visible light, ultraviolet, X-rays, gamma rays D) infrared, visible light, ultraviolet, X-rays, gamma rays, radio E) visible light, infrared, X-rays, ultraviolet, gamma rays, radio
C) radio, infrared, visible light, ultraviolet, X-rays, gamma rays
What is the end result of evolution for a star less massive than 8 solar masses? A) black hole B) neutron star C) white dwarf D) pulsar
C) white dwarf
How do astronomers observe astrophysical black holes if no light can escape from the event horizon of the black hole? A) We see light emitted by matter spiraling into the black hole that has not yet crossed the event horizon. B) We infer the black hole's gravitational effect on the motion of nearby stars. C) We see the gravitational waves emitted by black hole mergers. D) All of the above
D) All of the above
How does the light cone constrain your past, present, and future location? A) Your future must lie within your future light cone. B) Your past must lie within your past light cone. C) Regions of spacetime outside your light cone are not regions of spacetime you could ever reach. D) All of the above. E) A and B.
D) All of the above.
What do we know about the maximum mass of neutron stars? A) Theoretical arguments based on general relativity suggest that it is not much higher than 3 solar masses. B) Observations of pulsars tell us that it must be at least 2 solar masses. C) The precise limit is uncertain because our theoretical understanding of neutron degeneracy pressure is incomplete. D) All of the above.
D) All of the above.
Why can systems where matter accretes onto black holes be so luminous? A) Black holes radiate immense amounts of radiation via hawking radiation. B) Each black hole coexists with a white hole that emits immense amounts of light. C) Black holes accrete more matter than other objects with the same mass because their gravitational force is so much stronger. D) Black holes are very compact for their mass
D) Black holes are very compact for their mass
Julia and Ari are two astronauts traveling in opposite directions with a relative speed of 0.9 c. Which of the following is true? A) Ari thinks that Julia's clock runs fast, Julia thinks that Ari's clock runs slow. B) Julia thinks that Ari's clock runs fast, Ari thinks that Julia's clock runs slow. C) Both think that the other's clock runs fast. D) Both think that the other's clock runs slow
D) Both think that the other's clock runs slow
Which of the following statements about spacetime is correct? A) Newton invented the concept of spacetime. B) Spacetime is a combination of an absolute space and an absolute time. C) Einstein invented the concept of spacetime. D) Gravity can be understood to arise from the curvature of spacetime. E) All of the above.
D) Gravity can be understood to arise from the curvature of spacetime.
What happens next after a star uses up all the hydrogen in its core? A) It starts fusing helium in its core and the star contracts. B) It starts fusing helium in its core and the star expands. C) It starts burning hydrogen in a shell and the star contracts. D) It starts burning hydrogen in a shell and the star expands.
D) It starts burning hydrogen in a shell and the star expands.
Why would Newton's version of Kepler's third law be useful to an astronomer who wanted to study a distant black hole? A) It would help her to calculate distance to the black hole if the black hole is orbited by another star. B) It tells her that objects orbiting the black hole follow elliptical orbits. C) It would help her to calculate the power radiated by the black hole if the the black hole is orbited by another star. D) It would help her to calculate the mass of the black hole if the black hole is orbited by another star.
D) It would help her to calculate the mass of the black hole if the black hole is orbited by another star.
How are wavelength, frequency, and speed related for light traveling in space? A) Longer wavelength means higher frequency and lower speed. B) Longer wavelength means higher frequency and same speed. C) Longer wavelength means lower frequency and higher speed. D) Longer wavelength means lower frequency and same speed.
D) Longer wavelength means lower frequency and same speed.
Jody and Joy are identical twins. Jody stays on Earth while Joy travels at a large fraction of the speed of light to study a distant star system. When Joy returns, she is only 5 years older, but her sister has long since died as 200 years have passed on Earth. How can this aging difference be reconciled with the concept that different inertial observers in relative motion each perceive the other observer's clock to run slow? A) It cannot be reconciled. This scenario is not allowed by special relativity. B) Special relativity does not apply when the velocities are close to the speed of light. C) Special relativity only says that inertial observers in relative motion perceive each other's clocks to run slow. It does not require their clocks to run slowly by the same amount. D) Special relativity does not apply because Joy is not an inertial observer during this trip.
D) Special relativity does not apply because Joy is not an inertial observer during this trip.
Which of these parts of the electromagnetic spectrum corresponds to the most energetic photons? A) visible light B) radio waves C) infrared D) X-rays
D) X-rays
If you cross the event horizon of a Schwarzschild black hole, what must happen? A) The answer depends on which direction you crossed - inward or outward. B) You must enter a parallel universe. C) You are immediately ripped apart by the infinite spacetime curvature at the horizon. D) You are pulled towards the singularity.
D) You are pulled towards the singularity.
In general, what type(s) of energy does the E in the equation E = mc2 represent? A) gravitational potential energy only. B) rest mass energy only. C) kinetic energy only. D) both rest mass energy and kinetic energy. E) any type of energy.
D) both rest mass energy and kinetic energy.
An inertial observer is an observer who: A) has no inertia. B) has no velocity. C) has no mass. D) has no acceleration.
D) has no acceleration.
Without telescopes or other aid, we can look up and see the Moon in the night sky because it A) emits visible light. B) reflects infrared light. C) glows through radioactive decay. D) reflects visible light.
D) reflects visible light.
Which of the following does special relativity say inertial observers must agree on? A) the observers' masses. B) the time between events. C) the observers' lengths D) the observers' speed relative to each other
D) the observers' speed relative to each other
Which of the following is not a source of spacetime curvature in Einstein's field equations? A) mass B) light C) pressure D) time
D) time
Which of the following follows a geodesic? A) A photon. B) A planet in orbit around a star. C) A rocket accelerating out of Earth's gravity. D) All of the above. E) A and B only
E) A and B only
Which of the following is not a test that general relativity has passed? A) Mercury's perihelion precession. B) The bending of light from background stars by the Sun. C) Comparison of atomic clocks located at different distances from Earth's surface. D) Measurement of the change in the Moon's orbital radius using lasers. E) All of the above are tests that general relativity has passed.
E) All of the above are tests that general relativity has passed.
If you are an astronaut on a planet with twice the mass of the Earth, but one eighth the radius of the Earth, how would the planet's escape velocity compare to Earth's escape velocity? A) 1/4 as large as the Earth's escape velocity B) Half as large as the Earth's escape velocity. C) Same as the Earth's escape velocity. D) Twice the Earth's escape velocity. E) Four times the Earth's escape velocity.
E) Four times the Earth's escape velocity.
What made the detection of gravitational waves from the merger of neutron stars interesting to astronomers? A) The merger was more energetic than previous black hole mergers and thus provided a better test of general relativity. B) The merger was accompanied by an electromagnetic counterpart signal whereas previous black hole mergers did not coincide with detectable electromagnetic signals. C) The merger provides evidence that most of the heavy elements (e.g. gold) in the universe may have been produced in such mergers. D) All of the above. E) Only B and C.
E) Only B and C.
