Astronomy MCQ's (since quiz 3 and all 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
. 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
1. 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
11 Why are accreting black holes so hot that they primarily emit in the X-rays? They are very luminous and emitting area is small. They are very luminous and emitting area is large. They need to be hot for nuclear reactions to proceed. The emitting area is large and the accretion rate is large.
A
14 Hawking radiation is: the production of real particles (mostly photons) from gravity acting on virtual particles. the production of a special type of gravitational wave. not really radiation. something that occurs only for charged black holes.
A
16 The information paradox is a statement that: The information about how the black hole is created seems to be lost after the black hole evaporates. The information about objects that fall into a black hole is lost when those objects cross the event horizon. Information seems to be lost when quantum systems are measured. Black holes seem to contain an infinite amount of information.
A
2 Given what we learned about tidal forces, what type of black hole would be most effective at disrupting a Sun-like star million solar mass black hole billion solar mass black hole it should not depend on black hole mass
A
3 What observation of galaxies implies the existence of a supermassive black hole at its center? Average stellar velocities are too high near the galaxies centers. Rotational velocities are too high in the outer regions of galaxies. Rotational velocities are too low in the outer regions of galaxies. Galaxies seem to be moving away from us too quickly.
A
4 Why did observations of NASA's Compton Gamma Ray Observatory (CGRO) convince most astronomers that gamma ray bursts were most likely from outside our galaxy? Observations from CGRO showed that the bursts were isotropically distributed on the sky, which was inconsistent with an origin from galactic neutron stars. Observations from CGRO showed that the burst were very energetic, which meant they must be very far away to explain their relatively modest flux at Earth. Observations from CGRO discovered afterglows from material running into the surrounding interstellar gas, that allowed them to determine the galaxies where the burst originiated. Observations from CGRO actually supported the opposite view that gamma ray bursts occurred in our galaxy, which mislead astronomers for many years.
A
5 If Hawking radiation causes the mass to decrease, it also causes the event horizon area (entropy) of the black hole to decrease. What does the 2nd law of thermodynamics then imply about the Hawking radiation? The Hawking radiation must have the same or more entropy than what is lost by the black hole. The Hawking radiation must have the same or less entropy than what is gained by the black hole. The Hawking radiation must have zero entropy. The Hawking radiation must have negative entropy.
A
8 What do we primarily need to measure to infer a lower limit on the mass of a black hole in a binary star system? The orbital period and Doppler shift. The orbital period and the distance to the binary. The distance to the binary and the Doppler shift. The temperature of the companion star and the Doppler shift.
A
Lyman alpha is a prominent emission line seen in quasar spectra. It is emitted at 122 nm for an object at rest. At what wavelength would we observe this line if it were emitted by a quasar at redshift z=6.8? 952 nm 830 nm 722 nm 122 nm
A
Review: Why is this particular neutron star binary containing a pulsar so useful to astronomers? The pulsar is an accurate clock that allows us to measure small changes in the orbital period of the binary. The pulsar is an accurate clock that allows us to measure small changes in the neutron star spin period. We can directly measure the gravitational waves produced by this binary. The mass of one of the neutron stars in this system is above 3 Msun, placing important constraints on the theory of general relativity.
A
Since the event horizon of the black hole in the Galactic center still has a very small angular size, how can we hope to image the accretion flow on horizon scales? It can be imaged from the ground using radio telescopes located on different continents as interferometers. It can be imaged from the ground using a single large radio telescope. It is just barely imageable with the Hubble space telescope. It can be imaged from the ground in the near infrared using adaptive optics.
A
Why do astronomers expect observations of black hole mergers to require the measurement of incredibly small wave strain? Mergers of black hole are thought to be incredibly rare so that a typical event will happen very far from Earth and the gravitational waves will be weak by the time they reach us. Even the merger of black holes produces rather weak gravitational waves. Black hole mergers are thought to have only occurred in the very early universe so the gravitational waves will be weak because they have travelled billions of light years to reach us. The frequencies at which we can observe black holes with LIGO are very poorly matched to the incredibly low frequencies that gravitational waves will be emitted at.
A
How does LIGO detect gravitational waves? It looks for changes in the distance between sets of mirrors located at right angles to each other. It uses lasers in an interferometer. It measures variations in the Earth's gravitational acceleration. It looks for the same signal nearly simultaneously in two different detectors located a few miles apart.
A and B
15 In Hawking's original theory, what can determine the spectrum of the Hawking radiation? The black hole's mass. The formation history of the black hole. The black hole's spin. The age of the black hole. The black hole's position in space. Choose all that apply.
A and C
1 What do astronomers infer from observations thant almost every galaxy is moving away from us and ones that are more distant are moving away faster? We must be near the center of the universe. The universe is expanding everywhere. The universe is contracting everywhere. The Big Bang originated somewhere close to our own galaxy.
B
10 Why did it take astronomers so long to discover evidence for black holes using X-ray telescopes? Astronomers had not considered that any objects would be hot enough to emit X-rays. The Earth's atmosphere is opaque to X-rays so we had to wait until we could launch detectors into space. The technology to detect X-rays was not available until the 1960s. Black hole X-ray binaries are very faint X-ray sources.
B
11 Why do we not expect to see tidal disruption of Sun-like stars by black holes larger than about 108 Msun? Black holes larger than this mass are almost never observed. Black holes larger than this mass have tidal forces that are too weak to disrupt the star until it has already passed through the event horizon. Black holes larger than this mass are in galaxies that are so old that all of the Sun-like stars that could have been disrupted have already been disrupted. Black holes larger than this mass have gravity that is too weak to perturb the stars so that their orbits brings them close to the black hole.
B
13 If at 15 Msun black hole merges with a 30 Msun black hole and they form a single black hole of 43 Msun, how much energy must be radiated as gravitational waves? 3.6 x 1046 J 3.6 x 1047 J 3.6 x 1048 J 3.6 x 1049 J
B
2 What observation of galaxies implies the existence of dark matter? Average stellar velocities are too high near the galaxies centers. Rotational velocities are too high in the outer regions of galaxies. Rotational velocities are too low in the outer regions of galaxies. Galaxies seem to be moving away from us too quickly.
B
4 How does the LIGO interferometer work? It measures changes in the speed of light as the gravitational wave passes by It measures changes in the distance between mirrors as the gravitational wave passes by It measures changes in the Earth's gravitational acceleration as the gravitational wave passes by It measures changes in the Earth's radius at two different detectors as the gravitational wave passes by
B
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
Black hole spin affects all of the following aspects of accretion in black hole X-ray binaries. Based on what we've discussed, which is the most important to astronomers studying black holes? Spin affects the structure of the black hole insdie the event horizon. Spin determines the effective inner edge of the black hole accretion disk (the ISCO). Spin determines how much energy can be extracted via a Penrose like process. Spin affects the vertical thickness of the accretion disk.
B
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
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
So gas can fall into a black hole. Why does this matter? Gas falling into a black hole will cause it to grow and start radiating Hawking radiation that can be observed. Gas falling into a black hole loses gravitational potential energy and some of that can be radiated as light. Gas falling into a black hole loses kinetic energy and of that can be radiated as light. Gas clouds falling into a black hole becomes very dense due to tidal forces and forms stars that radiate intensely.
B
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
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
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
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
Why did observation of a pulsar in a binary allow astronomers to infer the existence of gravitational waves? Gravitational waves from black hole mergers modified the period of the binary as they passed by. We can measure the gradual shift in the stars' closest approach due to emission of gravitational waves. We can measure the change in the Doppler shift caused by the emission of gravitational waves. We observed the gravitational waves produced when the binary merged.
B
Why do quasar continuum peak in the ultraviolet while X-ray binaries peak in the X-rays? quasars are less luminous than X-ray binaries quasars have a much larger emitting area than X-ray binaries quasars are so highly redshifted that their X-rays come out in the ultraviolet the X-ray radiation emitted by quasars is absorbed by nearby gas an reradiated in the ultraviolet
B
Why would merging black hole binaries be stronger sources of gravitational waves than merging stars of the same mass? The black holes themselves are non-axisymmetric The black holes are compact enough that they can get very close to each other before merging. The gravity from the black holes is stronger. Merging stars of the same mass would produce more gravitational waves, but this is rarer than black hole mergers.
B
Why would these accretion disks be so hot that their thermal emission is in X-rays? large luminosity and large emitting area large luminosity and small emitting area small luminosity and large emitting area small luminosity and small emitting area
B
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 125 mph. What is your speed at the time of measurement? A) 215 mph B) 35 mph C) 75 mph D) 125 mph
B
12 How is black hole spin estimated in X-ray binaries? By taking an image of the accretion disk and finding the position of the inner edge of the disk. By modeling the spectrum of the accretion disk continuum emission. By modeling the relativistic effects on spectral emission lines. Astrophysical black holes are not thought to have significant spin so spin estimates are not considered useful. Choose all that apply.
B and C
9 What are the main pieces of evidence we use to differentiate a black hole binary from a neutron star binary? Black hole accretion disk emit in the X-rays but neutron star disks are cooler. We assume it is likely to be a black hole if its mass is larger than 3 Msun. We assume it is a neutron star if it shows pulsations or thermonuclear bursts. Choose all that apply.
B and C
8 Why do astronomers think that accretion onto the black hole in our galactic center is not very bright compared to accreting supermassive black holes in active galactic nuclei? The accretion flow is just as luminous as in quasars but most of the light is absorved by dust before reaching Earth. The gas that is available to accrete does not seem to make it down to radii comparable to the black hole event horizon. The gas that is available to accrete does not seem to make it down to radii comparable to the black hole event horizon. The gas that does accrete to the scale of the black hole event horizon is low density and not very efficient at emitting light. Choose all that apply.
B,C,D
Which of the following produce gravitational waves if general relativity is correct? A spinning black hole. A conductor directing a symphony. The Earth orbiting the Sun. A neutron star with a mountain on it.
B,C,D
. 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
1 If the Universe is infinite why can we only see 100 billion galaxies? Technological limitations. As long as we continue improving our telescopes, we will be able to see as many galaxies as we like. The cosmic microwave background forms a barrier that prevents us from seeing more distant galaxies We can only see galaxies whose light has had time to reach us travelling at the speed of light for the age of the universe The distance between galaxies gets larger as we look further away so it becomes increasingly difficult to see them.
C
13 What parameters would one need to measure to completely characterize and astrophysical black hole? Mass only. Mass and charge. Mass and spin. Mass and temperature. Mass and luminosity.
C
2 Why are accreting black holes thought to form jets? The jets are associated with the emission of Hawking radiation from the black hole's event horizon. Accreting black holes are not thought to form jets. This phenomenon only occurs for accreting neutron stars. Magnetic fields threading the accretion disk or black hole are wound up by rotation, which accelerates particles that then radiate. The jets are thought to form because of the relativistic beaming of light emitted on the approaching side of the accretion disk.
C
2 Why do galaxies collide while this almost never happens with stars? Stars move much slower than galaxies move Stars move much faster than galaxies move Galaxies are much closer together relative to their size than stars are. Galaxies have a much stronger mutual gravitational attraction than stars do.
C
3 Why do we think common envelope phases must occur? We see binaries that appear to be in a common envelope phase. The physics of the common envelope phase is well understood from theory. The final separation of some binaries with black holes or neutron stars are smaller than the radii of the original star. common envelope is the most common outcome in binaries due angular momentum losses in stellar winds.
C
4 If a typical quasar spectrum peaks around 100 nm, in what part of the electromagnetic spectrum would its peak be observed for a source at z=7? X-ray ultraviolet infrared radio
C
6 Quasars are more luminous than X-ray binaries, but their emission comes out at longer wavelengths, indicating cooler temperature for the accretion disk. How could a more luminous accretion flow give rise to a lower temperature? Temperature is lower because flux is lower due to smaller emitting area. Temperature is lower because flux is higher due to smaller emitting area. Temperature is lower because flux is lower due to larger emitting area. Temperature is lower because flux is higher due to larger emitting area.
C
6 What is this dependence only on the spin, mass, and charge reminiscent of? The equivalence principle Cosmic censorship hypothesis "No hair" theorem Penrose process
C
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
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
How much energy is radiated by a non-spinning black hole that accretes 10-7 Msun per year? 3.4 x 1029 W 3.4 x 1030 W 3.4 x 1031 W 3.4 x 1032 W
C
Imagine your insane physicist friend gives you 5 micrograms (5×10−9 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 × 108 joules D) 9 × 1011 joules
C
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
Once an accretion disk forms, how does matter lose angular momentum in order to slowly move towards the black hole? The matter does not need to lose angular momentum to move inwards. The viscosity caused by collisions between particles provides friction between neighboring rings in the disk. The turbulent magnetic fields provide friction between neighboring rings in the disk. The radiation forces from light emitted by the accretion disk provide friction between neighboring rings in the disk.
C
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
So, if even a tiny amount of angular momentum makes it hard for gas to fall directly into the black hole, how does anything end up there? It does not. Black holes don't grow much after they are born. The angular momentum of the gas will slowly decrease with time because angular momentum is not a conserved quantity. Gas can interact with itself so that some gas loses and some gains angular momentum, allowing a fraction of the gas to fall in.
C
What do astronomers need to measure masses of black holes in binaries? orbital period, distance, and temperature orbital period, Doppler shift, and distance orbital period, Doppler shift, and viewing angle Doppler shift, viewing angle, and distance Doppler shift, distance, and luminosity
C
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
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
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
Why are there usually two low tides per day at any location on the Earth? A) One low tide is caused by the Moons gravity and a second low tide is caused by the Suns 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
Why can systems where matter accretes onto black holes be so luminous? Each black hole coexists with a white hole that emits immense amounts of light. Black holes radiate immense amounts of radiation via hawking radiation. Black holes are very compact for their mass. Black holes accrete more matter than other objects with the same mass because their gravitational force is so much stronger.
C
Why do astronomers think the accretion disks in X-ray binaries form a collimated jet? They observe long narrow structures in image of the X-ray emission from X-ray binaries. They observe long narrow structures in images of radio emission from X-ray binaries. They assume radio emission in X-ray binaries arises from the same mechanism seen in quasars. The spectral properties of the X-ray emission are difficult to understand without invoking a relativistically beamed jet.
C
Why do astronomers think the black hole in our galactic center has the event horizon with the largest angular size? We believe it is the closest black hole to our location at Earth. We believe it is the most massive black hole we have observed and therefore has the largest Schwarzschild radius. We believe it has the largest ratio of Schwarzschild radius to distance from Earth of any black hole. We believe it has the largest ratio of Schwarzschild radius to mass of any black hole.
C
Based on the above criteria, which of the following would be strong sources of gravitational waves? spinning black hole spinning neutron star spinning neutron star with a mountain on it binary star system
C andD
. 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
. 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
1 What property would a star need to have to get close enough to the black hole to be ripped apart? high velocity low velocity high angular momentum low angular momentum
D
12 How luminous (in gravitational waves) was the first black hole merger detected by LIGO at its peak? It was comparable to the luminosity of the Sun. It was comparable to the luminosity of the entire Milky way galaxy. It was comparable to the luminosity of a gamma ray burst. It was comparable to the luminosity of all the stars in the observable universe.
D
13 The area of a black hole event horizon: is not well defined. must always increase. must always decrease. must always increase, except when Hawking radiation is emitted.
D
14 In both the first and second LIGO detections, the final black hole was found to have a spin parameter of a = 0.7, meaning that the black hole was spinning at about 0.7 times its maximum possible value. What does this tell us about the spins of the initial black holes? The sum of their spins must be nearly equal to 0.7. The sum of their spins must be less than 0.7. The sum of their spins must be more than 0.7. Not much, because the spin of the final black hole could be dominated by the orbital angular momentum of the merging black holes.
D
3 How were gamma ray bursts first discovered or predicted? Despite their name, gamma ray burst were first discovered by their radio emission and it was only later realized they mostly emitted gamma rays. NASA launched the first gamma ray astronomical observatories into space and gamma ray burst turned out to be the brightest gamma ray sources. Gamma ray bursts were predicted from models of black hole formation. Gamma ray bursts were discovered by gamma ray detectors onboard satellites that were looking for nuclear detonations.
D
4 If you have 8 (non-interacting) particles in a system, what is the probability that they will all be located in on the left side? (Hint: consider case of 1, 2, 3,... particles.) 1/2 1/8 1/(82) (1/2)8
D
5 What is the generally accepted theoretical explanation for gamma ray bursts? Merger of two neutron stars. Collapse of the core of a massive star. Accretion onto a newly formed black hole. All of the above.
D
5 Where did the energy of the gravitational waves come from? The gravitational potential energy of the black holes as their orbit shrank The orbital energy of the black holes as their orbit shrank The rest mass energy of the black holes that was lost when they merged All of the above
D
6 What fraction of stars in the stellar neighborhood are binary stars? Binaries are extremely rare. About 1/100 About 1/10 About 2/3 Almost all stars are in binaries. The Sun is a rare exception.
D
7 What do adaptive optics systems on telescopes allow astronomers to do? They allow astronomers to control the telescope over the internet. They allow astronomers to combine the signals from two different telescopes. They allow astronomers to adjust the telescope for changing weather conditions. They allow astronomers to deform a telescopes mirror to correct for turbulence in the atmosphere.
D
7 What is the theoretical argument to explain why observable black hole binaries are rare? Massive stars that form black holes are a small fraction of stars. Because the stars had to have survived a common envelope phase to decrease the orbital separation. Because most binaries are probably disrupted when the more massive star undergoes supernova. All of the above.
D
An inertial observer is an observer who: A) has no inertia. B) has no velocity. C) has no mass. D) has no acceleration.
D
Given a measured Doppler shift, the associated line-of-sight velocity depends on our viewing angle. How could we measure this angle? We cannot measure this angle. We measure the angle dependent lensing from the black hole. We use two different estimates of the Doppler shift at different times in the stars orbit. We measure the changes in the observed flux from the companion star as it orbits.
D
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
How does LIGO identify at black hole merger event? It simply looks for very large oscillations at the correct frequency. It looks for very large oscillations coincident with the detection of a gamma ray burst. It looks for specific waveforms that can be computed analytically. It looks for specific waveforms that must be computed using numerical simulations.
D
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
If a powerful gravitational wave passed through you body, moving from your back to your chest, what would happen to your body? You would experience an oscillation in your height only. You would experience an oscillation in your width only. Your width and height would both oscillate in such a way that you get taller and wider at the same time. Your width and height would both oscillate in such a way that you would get taller as you got narrower and shorter as you got wider.
D
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
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
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
What makes the stars close to the galactic center black hole so difficult to observe? They are so close to the black hole that their light is redshifted. They are very low luminosity. They are not resolvable, even with adaptive optics. They are viewed through a large amount of dust.
D
What was so mysterious about quasars when astronomers first realized how distance they were? Their radio lobes required incredibly large magnetic field energies to generate. Their optical emission was much more luminous than the brightest galaxies then observed. Their variability implied they must be coming from regions more than a thousand times smaller than the size of galaxies. All of the above. Only a and b.
D
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
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. 176 D) It would help her to calculate the mass of the black hole if the black hole is orbited by another star.
D
1 How do astronomers see astrophysical black holes if no light can escape from the event horizon of the black hole? We look for light emitted by matter close to the black hole that has not yet crossed the event horizon. We look for the black hole's gravitational effect on the motion of nearby stars. We look for the emission from the black holes corresponding white hole. All of the above Both a and b
E
12 Why are the observable properties of tidal disruption events difficult to predict from theory? They are challenging to simulate with computers. They involve accretion rates that are so large that the light emitted can push accreting gas away from the black hole. They require us to know what happens to the star after it has passed inside the event horizon. All of the above. Only A and B.
E
2 Why do some astrophysical objects form spheres and others form disks? Disks form when the initial distribution of matter is created by an explosion of a spherical object. Disks form when the initial distribution of matter has low angular momentum. Disks form when the initial distribution of matter is very cold. Disks form when the initial distribution fo matter is very hot. Disks form when the initial distribution of matter has high angular momentum.
E
The universe is filled with light at microwave wavelengths called the cosmic microwave background. This light was created a few hundred thousand years after the big bang. When we observe this light with our telescopes, it has traveled over 13 billion years (in our reference frame) to reach us. In the frame of the light, how much time passes between emission in the early universe and absorption in our detector? (Hint: what is the Lorentz factor for v = c and what does it mean for time dilation?) A) About 13 billion years B) About 10 years C) About 100 billion years D) About 10 billion years E) No time passes in the frame of the light. Emission and absorption are effectively simultaneous.
E
Tidal disruption events are difficult to observe. Why? they are rare events in any single galaxy they are short-lived by astronomical standards they do not emit much light all of the above only (a) and (b)
E
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
Why is the black hole in our galactic center not very luminous? There is is not much gas around. Very little of the gas actually makes it to the black hole. The gas that does make it to the black hole does not radiate efficiently all of the above only b and c
E
