Spring 2019 ASTR 2030 Clicker Questions

Spring 2019 ASTR 2030 Homepage

Spring 2019 ASTR 2030 Black Holes: Clicker Questions

Mon 2019 Jan 14 (not graded):

Will you get an A in this class?
A. Yes, I am at least 90% sure of it.
B. I think I have a better than 50% chance.
C. Probably not.
Wed 2019 Jan 16 (not graded):
For what kinds of black holes do astronomers see evidence?
A. Exploding mini-black holes.
B. Stellar-sized black holes.
C. Supermassive black holes at the centers of galaxies.
D. Both B and C.
E. The Universe as a whole is a black hole.
Why does the spaceship not go closer to the black hole?
A. Because the black hole would suck in the spaceship, regardless of how hard the spaceship fired its rockets.
B. Because it would take too much rocket fuel to go closer.
C. Because the acceleration needed to stay outside the event horizon would squash a human.
D. Because the x-rays would kill a human.
E. Because the tidal forces would tear a human apart.
Will the probe fall into the black hole?
A. Yes.
B. No.
How long does Thorne say that our journey to the center of the Milky Way, 30,000 lightyears distant, will take, from our point of view? We accelerate at one gee (one Earth gravity) for the first half of the journey, then decelerate at one gee for the second half.
A. Almost no time.
B. 20 years.
C. 30,000 years.
D. 60,000 years.
E. Much longer than any of the above.
Fri 2019 Jan 18:
The tidal force is the difference in the gravitational force between two parts of an object (e.g. between your head and your toes). The tidal force of a black hole will tear you apart:
A. at the event horizon;
B. somewhere inside the event horizon;
C. at the singularity;
D. inside the event horizon if the black hole has a stellar-size mass, or outside the horizon if the black hole is supermassive;
E. outside the event horizon if the black hole has a stellar-size mass, or inside the horizon if the black hole is supermassive.
If the postulates of special relativity are correct, would the light have moved differently if Cerulean, not Vermilion, had emitted the light?
A. Yes.
B. No.
On this spacetime diagram, how fast is Cerulean moving relative to Vermilion, in units of the speed of light?
A. 0.
B. 1/2.
C. 1.
D. 2.
E. The information on the diagram is insufficient to answer the question.
Wed 2019 Jan 23:
Why is the wavelike nature of light difficult to see?
A. Because the speed of light is so large.
B. Because the wavelengths of visible light are so short.
C. Because white light is a mixture of many wavelengths.
D. Because our eyes are sensitive only to three colors.
E. B & C.
Is this a cube?
A. Yes, seen in projection.
B. No.

Fri 2019 Jan 25:
According to Thorne Ch 1, what influence did the Michelson-Morley (1887) experiment have on Einstein's thinking?
A. Michelson and Morley's failure to detect any difference in the speed of light in different directions suggested to Einstein that the speed of light is a universal constant.
B. Michelson and Morley's failure to detect the motion of the Earth through the aether suggested to Einstein that there is no aether, no absolute space or time.
C. It caused Einstein to think that motion through the aether would cause clocks to run slow and rulers to contract.
D. It provoked Einstein to think about Maxwell's equations of electromagnetism, which showed that light is electromagnetic waves.
E. Very little.
If Cerulean were moving as shown relative to Vermilion, which line would be a “now line” for Cerulean?
A.
B.
C.
D.
E.

Mon 2019 Jan 28:
Is this a line of simultaneity for twin on return?
A. Yes.
B. No.
On your way out to Alpha Cen, you appear to me, watching you through a telescope on Earth, to move at what speed?
A. 0;
B. ½ c;
C. Near c;
D. 2 c;
E. Near infinite speed.
On your way back from Alpha Cen, you appear to me, watching you through a telescope on Earth, to move at what speed?
A. 0;
B. ½ c;
C. Near c;
D. 2 c;
E. Near infinite speed.
If round-trip time is 8 years from my (Earth) perspective, then the round-trip time from your (traveler's) perspective is:
A. less than 8 years;
B. 8 years;
C. more than 8 years.
Wed 2019 Jan 30:
After the round-trip to Alpha Cen, the Earth-bound and traveling persons, now at rest relative to each other, compare their watches. They find that:
A. the traveling person's watch is running slow;
B. their watches are both running at the same rate;
C. the traveling person's watch is running fast;
D. they both think each other's watch is running slow.
When you accelerate to relativistic velocities, the view ahead appears to shrink. Why?
A. Because you are moving away from the scene ahead.
B. Because of Lorentz contraction.
C. Because of special relativistic aberration.
D. Because acceleration curves space.
If you travel through a scene at near the speed of light, clocks attached to the scene ahead appear:
A. slowed down compared to your own clock;
B. to run the same rate as your own clock;
C. speeded up compared to your own clock.
Mon 2019 Feb 4:
What “breaks the symmetry” between you and your twin, that allows the twin to be younger than you on return?
A. On the outward journey, the velocity at which the twin sees you recede is different from the velocity at which you see the twin recede; and then on the return journey, the velocity at which the twin sees you return is different from the velocity at which you see the twin return.
B. There is no difference, so in fact you must both age the same.
C. Twin moved through space, whereas you did not.
D. Twin accelerated (at turnaround at Alpha), whereas you did not.
E. Twin experienced a sudden loss of time at Alpha.
Your twin watches you on Earth through a telescope. At the moment that the twin accelerates at Alpha, the twin sees your clock:
A. Run at the same slowed-down rate both before and after accelerating.
B. Suddenly change from 2 years to 8 years.
C. Suddenly speed up.
D. Suddenly slow down.
E. Change from running forward to runing backward.
Very Long Baseline Interferometry (VLBI) observations of the quasar 3C273 show blobs emerging at 8c. This indicates that:
A. The jet is moving faster than c.
B. Special Relativity is wrong.
C. The blob is not a parcel of matter, but rather a wave of brightness passing along the jet.
D. The jet is pointed almost towards us, and is moving at close to c.
E. The jet is pointed away from us, and is moving at close to c.
Why is a second jet not observed in 3C273?
A. There is no second jet.
B. Aberration bends the second jet out of view.
C. The second jet is relativistically dimmed out of view.
D. The second jet is relativistically redshifted out of view.
E. The second jet is behind the quasar, which obscures it.
Will the spaceship fit inside the space station?
A. Yes.
B. No.
Wed 2019 Feb 6:
Not graded: Do you understand time dilation?
A. I think so!
B. I understand the diagram we filled in two weeks ago, but not much more.
C. I think I could maybe understand if I thought more about it.
D. I have no clue.
Not graded: Do you understand Lorentz contraction?
A. I think so!
B. I understand the diagram we filled in two weeks ago, but not much more.
C. I think I could maybe understand if I thought more about it.
D. I have no clue.
When you move through a scene at near the speed of light, which of the following is not true?
A. The scene ahead shrinks.
B. The scene ahead is blueshifted.
C. The scene ahead appears brightened.
D. Clocks on the scene ahead appear speeded up.
E. The scene ahead appears slowed down by time dilation.
Mon 2019 Feb 18:
(No grade). Vote for best relativistic scene.
Astronauts orbiting Earth in the Space Station feel weightless because:
A. There is no gravity in space;
B. The Space Station and the astronauts are in free fall.
Suppose you watch this scene while falling freely. According to the Principle of Equivalence, what kind of trajectory will the cannonball follow from your perspective (relative to you)?
A. A vertical line.
B. A straight line.
C. A curved (parabolic) line.
According to Special Relativity, does B see the light from A to be redshifted or blueshifted?
A. B sees the light to be redshifted (lower energy) compared to A.
B. B sees the light to have the same energy as A.
C. B sees the light to be blueshifted (higher energy) compared to A.
You are in flat space. You swing a clock on a rope in a circle around you, so that the clock is moving at near the speed of light relative to you. According to Special Relativity, the clock will appear to you to tick:
A. Slow;
B. At the same rate as your own clock;
C. Fast;
D. None of the above.
Wed 2019 Feb 20:
In the situation of the previous question, the object therefore appears to you (according to Special Relativity):
A. Redshifted;
B. Neither redshifted nor blueshifted;
C. Blueshifted.
What is Einstein's (Strong) Principle of Equivalence?
A. Mass and energy are equivalent.
B. Space and time are equivalent.
C. Objects fall under gravity at the same rate regardless of their mass.
D. The rules of physics in a gravitating frame are the same as those in an accelerating frame.
E. Spacetime is curved.
Will the probe fall into the black hole?
A. Yes.
B. No.
Fri 2019 Feb 22:
According to Thorne Ch 2, Einstein came up with the Principle of Equivalence:
A. In 1905, the same year he published his theory of Special Relativity;
B. In 1907, while preparing an invited review on Special Relativity;
C. In 1915, after 10 years of intermittent work;
D. Over a period of several decades, up to nearly the end of his life in 1955;
E. Actually it was Poincaré, not Einstein, who first proposed the Principle of Equivalence.
According to Thorne Ch 2, an astronaut in outer space can detect that spacetime is curved from:
A. Measuring the speed of light (with ruler, mirror, and clock);
B. The presence of a gravitational force;
C. The presence of a tidal force (difference in gravitational force between two points a small distance apart);
D. Outer space is empty, so spacetime there must be flat, not curved;
E. The Principle of Equivalence implies that the astronaut cannot detect that spacetime is curved.
According to the river model of black holes, a person who free-falls through the horizon of a black hole appears to an outside observer to freeze and become highly redshifted at the horizon because:
A. The black hole freezes at its horizon, and never actually collapses;
B. The person freezes at the horizon, and never actually falls through;
C. The curvature of space becomes infinite at the horizon;
D. The closer to the horizon a photon is emitted, the longer the photon takes to forge against the inrushing torrent of space to reach an outside observer;
E. It's not true: an outside observer sees the infaller become highly speeded up and blueshifted.
According to the river model of black holes, a person who free-falls through the horizon of a black hole:
A. Experiences time to come to a halt at the horizon;
B. Experiences an infinite curvature, a singularity, at the horizon;
C. Is tidally torn apart at the horizon;
D. Sees an infinitely bright shaft of light directly above them at the horizon;
E. Experiences nothing special at the horizon.
Mon 2019 Feb 25:
Does the Schwarzschild geometry describe the geometry of empty space around the Sun?
A. Yes, to a good approximation.
B. No, not at all.
How to get to the Parallel Universe?
A. Accelerate towards the Parallel Universe.
B. Accelerate away from the Parallel Universe.
C. A, then go backwards in time.
D. B, then go backwards in time.
E. It's impossible.
Wed 2019 Feb 27:
What evidence most convincingly suggests that there is a supermassive black hole at the center of our own Milky Way?
A. The black hole causes gravitational lensing.
B. The supermassive black hole is in an x-ray binary star system.
C. Hubble Space Telescope observations show gas swirling down a vortex.
D. A relativistic jet is seen coming out of the core of the Milky Way.
E. Measurements of the velocities of stars at the center of the Milky Way indicate a large mass in a small space.
The curve of enclosed mass versus radius has a flat part, then an upturn at larger radius? What mass causes these?
A. All the mass is produced by stars.
B. All the mass is produced by a black hole.
C. A point mass causes the flat part; stars cause the upturn.
D. A point mass causes the flat part; an accretion disk causes the upturn.
E. A star causes the flat part; a black hole cause the upturn.
From a safe distance, we watch a spherical, pressureless star collapse to a black hole. What will we see?
A. The star will appear to freeze when at the horizon radius, and never collapse.
B. The star will appear to branch into a wormhole and white hole, before becoming a black hole.
C. The star will appear to collapse to a singularity.
When the mass of a black hole increases, its horizon expands. Does the horizon appear to engulf stuff that previously fell through the horizon?
A. Yes, stuff that previously fell into the black hole disappears.
B. No, stuff that previously fell into the black hole remains frozen at the horizon, appearing to expand with the horizon.
If, as seen by an outside observer, a star appears never to collapse through its horizon, does the star ever actually collapse?
A. Yes.
B. No.
Wed 2019 Mar 6:
Where do the x-rays in an x-ray binary like Cyg X-1 come from?
A. Light from the companion star, gravitationally lensed and blueshifted by the black hole.
B. The black hole.
C. Hot gas in an accretion disk spiralling on to the black hole.
D. A jet emerging from near the black hole.
E. Decay of radioactive elements synthesized near the black hole.
Oppenheimer and Snyder carried out the first calculation of the collapse of an idealized, spherical, uniform, pressureless star in 1939. They found that:
A. All observers would see the star collapse to a singularity;
B. All observers would see the star freeze at its horizon;
C. An observer collapsing with the star would find that it collapsed, whereas a distant observer would see the star freeze at its horizon.
According to Thorne Ch 3, Einstein rejected black holes (which he called “Schwarzschild singularities”) because:
A. There was no observational evidence for black holes;
B. It was absurd to think that nature could actually make such an extreme object;
C. A black hole has a singularity at its horizon, and singularities should not exist in nature;
D. A black hole has a central singularity, where spacetime comes to an end, which is impossible;
E. A black hole would curve space so much that it would swallow itself and disappear.
Fri 2019 Mar 8:
According to Thorne Ch 6, what breakthrough persuaded physicists that the Schwarzschild solution might represent an object that could actually exist in physical reality (in Thorne's words, “What converted Wheeler from a skeptic of black holes to a believer and advocate?”)?
A. Gullstrand and Painlevé's discovery in 1921 of coordinates that showed space flowing like a river into the black hole.
B. Zwicky's discovery in the 1930s of supernovae, which might represent the creation of a black hole.
C. Oppenheimer and Snyder's 1939 calculation that a collapsing star would appear to an outside observer to freeze at its horizon, but would appear to an observer on the star's surface to collapse through the horizon to zero radius.
D. Finkelstein's 1958 discovery of a coordinate system that showed that light could fall through the horizon.
E. Observations around 1970 that seemed to establish that Cygnus X-1 contains a black hole.
From outside the horizon, you watch your friend free-fall into a black hole. You talk to each other constantly via a direct radio link.
A. You both hear each other's voice continue almost normally.
B. You both hear each other's voice become much deeper.
C. You both hear each other's voice become much higher.
D. You hear your friend's voice become much deeper, while she hears your voice continue almost normally.
E. You hear your friend's voice become much deeper, while she hears your voice become much higher.
In order to fall into the black hole from this unstable circular orbit, we should do what?
A. Stop firing on our thrusters.
B. Execute a short forward burst on our thrusters.
C. Execute a short reverse burst on our thrusters.
D. The only way to fall in is to fire thrusters continuously.
Mon 2019 Mar 11:
As you approach the inner horizon of a charged (or rotating) black hole, you see the outside Universe:
A. Disappear into blackness;
B. Gravitationally lensed, but otherwise fairly normal;
C. Concentrate into an immensely bright, blueshifted point.
A Penrose diagram is a kind of spacetime diagram, in which time proceeds upwards, space fills out horizontal dimensions, and light goes at 45°. What is a Penrose diagram useful for?
A. Illustrating and resolving paradoxes in special relativity;
B. Depicting the curvature of spacetime around a gravitating object;
C. Depicting the causal structure of spacetimes, especially complicated spacetimes like black holes;
D. Depicting interactions between particles in high energy physics;
E. Showing off your IQ.
From the point of view of an observer outside the outer horizon of a white hole, is the white hole gravitationally attractive or gravitationally repulsive?
A. Attractive.
B. Repulsive.
C. Neither.
Mon 2019 Mar 18:
You free-fall into the rotating, supermassive black hole at the center of the Galaxy. What kills you?
A. The gravitational acceleration crushes you.
B. The tidal force tears you apart near the horizon.
C. High energy radiation from gas in an accretion disk kills you.
D. You are vaporized at the inflationary instability at the inner horizon.
E. You die at the central singularity.
According to Thorne Ch 8, how were astronomers, in 1971, able to identify Cyg X-1 definitely with the star HDE 226868?
A. Because HDE 226868 had a peculiar spectrum.
B. Because both objects varied with same 5.6 day binary period.
C. Because a radio flare from the position of HDE 226868 coincided with an x-ray flare from Cyg X-1.
D. Because an occultation of Cyg X-1 by the moon pinpointed its location at that of HDE 226868.
E. With the advent of high resolution x-ray telescopes, the positions of Cyg X-1 and HDE 226868 were found to coincide precisely within one arcsecond.
According to Thorne Ch 9, what is the brightest radio source in the sky?
A. The Sun.
B. Jupiter.
C. The x-ray binary Sco X-1.
D. The central regions of the Milky Way.
E. The quasar 3C 273.
If x-rays from an AGN vary on a timescale of one day, then the AGN is probably:
A. Smaller than one lightday across.
B. Larger than one lightday across.
C. Variability places no constraint on the size of the AGN.
D. A black hole.
Wed 2019 Apr 3:
What does the silence (in the first scene of “Contact”) mean?
A. Sound waves cannot go through space.
B. Radio waves cannot go through space.
C. Radio waves from Earth have not yet reached this distance.
D. Radio waves from Earth are too faint to reach this distance.
E. The Universe is large.
What will Ellie Arroway's boyfriend Palmer Joss turn out to be, professionally? (What would generate most conflict?)
A. A scientist.
B. An artist.
C. A journalist/writer.
D. A religious person.
E. A multi-billionaire.
Who is “the leader of the scientific team that made this remarkable discovery” who will take the podium?
A. Ellie Arroway.
B. David Drumlin.
Who does Ellie meet on the beach?
A. Herself as a young girl.
B. Drumlin.
C. Her father.
D. An alien, masquerading as her father.
E. God.
Fri 2019 Apr 5:
Who is clearly the hero of this movie?
A. Captain Dan Holland (Robert Forster).
B. Dr. Kate McCrae (Yvette Mimieux).
C. The robot, Vincent.
D. The black hole.
E. There isn't a clear hero.
Why does the dialog suck?
A. Because the script writer cannot write.
B. Because the actors cannot act.
C. Because the story is boring.
D. Because it's a Walt Disney movie aimed at kids.
E. Because there is no emotional connection or conflict between the characters.
What is the best way to avoid being pulled into the black hole?
A. Fire rockets continuously.
B. Invent anti-gravity (the movie solution).
C. Go into orbit, rely on centrifugal force.
D. Reduce the mass of the ship by throwing almost everything overboard.
E. Fall into the black hole and get frozen at its horizon.
Who will the villain turn out to be?
A. Journalist Harry Booth (Ernest Borgnine).
B. Dr. Alex Durant (Anthony Perkins, the Psycho guy).
C. Maximillian, an evil robot.
D. A mad German scientist who wears a white coat and who has turned all his crew into mindless robots.
E. There will not be a discernible villain.
Not graded: The climax of the movie is: The orange jello knocks the ship into the black hole, and:
A. The villains fall into the black hole, killing them, but the heros manage to escape to safety just in time.
B. The heros and villains have an all-out battle as they fall into the black hole (with an intense one-on-one between Vince and Maximilian), all the villains are killed, and all the heros escape through a wormhole.
C. The crew who had been turned into mindless robots are magically restored to life inside the black hole, and all the good guys escape through a wormhole.
D. Reinhardt is crushed by a beam, and goes to “hell” inside the black hole, while our heros fly through a “heavenly” wormhole to safety.
E. All die inside the black hole, excepting that Vince rescues Bob the Texan robot.
Mon 2019 Apr 8:
When you, a human, try to compress ordinary solid or liquid matter, what happens to the electrons orbiting nuclei in atoms?
A. They orbit much slower.
B. They hardly change their orbits.
C. They orbit much faster.
D. They move so fast that they escape the nuclei.
E. They jiggle around randomly.
Planets are made of solid/liquid matter, which is almost incompressible. Their density (mass/volume) equals atomic density, which is constant. What does the imply about the relation between mass M and radius R of planets?
A. The radius R is constant, independent of mass M.
B. M ∝ R.
C. M ∝ R².
D. M ∝ R³.
E. M ∝ R^1/3.
Eddington's paradox:
If the charactistic velocity v of atoms inside a star obeys v ≈ (GM/R)^1/2, and if the temperature T of atoms increases with their velocity as T ∝ v², then as a star decreases in temperature T (at fixed mass M), then its radius R should:
A. Decrease.
B. Remain the same.
C. Increase.
Suppose you put an electron in a box and removed as much energy as possible from the electron. Would the electron:
A. Stop moving?
B. Have a small but finite velocity?
Suppose you made the box smaller (and kept it at absolute zero temperature). Would the electron:
A. Remain at rest?
B. Go slower?
C. Go faster?
D. Stay the same velocity?
E. You could not make the box smaller.
Wed 2019 Apr 10:
The Schwarzschild diameter of a black hole is \(\dfrac{4 G M}{c^2}\). The Schwarzschild diameter of the \(M = 6 \times 10^9\) solar mass supermassive black hole in M87 is \(3.6 × 10^{10} ~{\rm km}\) = 2.5 times the orbital diameter of Pluto = 1.5 light days.
On what timescale do you expect the M87 black hole to vary?
A. Seconds.
B. Hours.
C. Days.
D. Years.
E. Centuries.
Mon 2019 Apr 15:
What kind of pressure holds up a white dwarf star against its own gravity?
A. The pressure of a liquid or solid of atoms.
B. The pressure of a gas of atoms.
C. The pressure of a hot gas of nuclei and electrons (a plasma).
D. Electron degeneracy pressure.
E. Neutron degeneracy pressure.
The transition between atomic pressure and electron degeneracy pressure in cold matter at very high density occurs when:
A. The matter is cooled to absolute zero temperature;
B. The matter is heated to the point where the electrons are ionized;
C. The electrons are compressed to the point where their velocities exceed the atomic velocity c/137;
D. The electrons are compressed to the point where their velocities approach the speed of light c;
E. The electrons and protons fuse into neutrons.
According to Thorne Ch 4, a white dwarf becomes highly compressible when it reaches the Chandrasekhar limit of 1.4 solar masses, at which point the white dwarf collapses. Why does the gas become so compressible?
A. The matter ceases to be solid or liquid.
B. Electron velocities exceed the atomic velocity, and are ionized out of atoms.
C. Electrons become relativistic (move at almost the speed of light), and can move no faster.
D. The temperature increases enormously.
E. A supernova explosion occurs.
The fact that pulsars were observed to pulse at several different radio frequencies ruled out the possibility that pulsars were LGM (Little Green Men). Why?
A. Because any signal from LGM would be too faint to be detectable.
B. Because LGM would probably not use radio waves.
C. Because LGM would emit only at a single narrow frequency.
D. Because LGM would emit a complicated signal, not just pulses.
E. Because the probability of LGM existing is tiny.
Wed 2019 Apr 17:
Who discovered pulsars, now known to be rotating neutron stars?
A. Chandrasekhar.
B. Sir Arthur Stanley Eddington.
C. Tony Hewish and Martin Ryle, who won the Nobel Prize for the discovery of pulsars.
D. Jocelyn Bell, as a graduate student at Cambridge.
E. Shep Doeleman, leader of the Event Horizon Telescope Collaboration.
What type of supernova is this?
A. Core collapse.
B. Thermonuclear.
You drop a basketball and a superball together, the superball on top of the basketball. How high does the superball bounce?
A. Lower than the height from which it was dropped.
B. To roughly the same height as from which it was dropped.
C. Higher than the height from which it was dropped.
Repeat the experiment with a smaller superball. Does the smaller superball bounce lower or higher than the larger superball?
A. Lower.
B. Roughly the same.
C. Higher.
Both types of supernova (core collapse and thermonuclear) are initiated by the collapse of an electron-degenerate core that reaches the Chandrasekhar limit of 1.4 solar masses. What causes the difference in outcomes?
A. The composition of the core, iron versus carbon-oxygen.
B. A difference in the mass of the envelope surrounding the core.
C. The gravity of the core.
D. Magnetic fields.
E. Chance.
Fri 2019 Apr 19:
What is the significance of the fact that the neutron stars in the Hulse-Taylor binary are both near 1.4 solar masses (1.4414 and 1.3867 suns)?
A. They formed from the collapse of a white dwarf that reached the Chandrasekhar limit.
B. That is the maximum mass of a neutron star.
C. Pulsars are rotating neutron stars.
D. At 1.4 solar masses, a neutron star is pulsationally unstable.
E. Neutron stars that massive will form a black hole when they merge.
In the first ever detected merger of two black holes, GW150914, the starting masses of the black hole pair were 29 and 36 suns, but the mass of the resulting single black hole was 62 suns, which is 3 suns less than the sum 29 + 36 = 65 suns of the original pair. Where did the energy in the missing 3 suns go to?
A. A supernova.
B. A jet.
C. Gravitational waves.
D. They disappeared inside the black hole.
E. In general relativity, mass-energy is not conserved.
As GW150914 approached the merger climax, the separation between wave peaks was a bit less than 0.01 seconds. What was the approximate wavelength of the gravitational waves detected?
A. About 10^–3 times the size of a proton nucleus.
B. About the size of a proton nucleus.
C. About the size of an atom.
D. About the wavelength of visible light.
E. About the size of the merging black hole system (about 1000 km).
Why does the detection of a burst of gamma rays 2 seconds after the gravitational wave signal in GW170817 imply that the speed of gravitational waves is the speed of light?
A. Because gamma-rays are a kind of gravitational wave.
B. Because general relativity predicts that gravitational waves move at the speed of light.
C. Because the signal travelled the same distance, 130 million lightyears, in the same time.
D. Because extremely energetic particles must move at the speed of light.
E. Actually, the fact that the gamma-ray signal was delayed by 2 seconds implies that gravity moves slightly faster than light.
Mon 2019 Apr 22:
In a gravitational wave interferometer such as LIGO, why must the distance between the mirrors along an arm (4 km) be much less than a wavelength of a gravitational wave from the merger of a stellar-mass binary (10s to 1000s of km), in order to track the wave accurately?
A. In any telescope, the size of the detector must be greater than the wavelength.
B. In any telescope, the size of the detector must be less than the wavelength.
C. Because the distance between the mirrors must be measured more rapidly than the distance is changing.
D. The further apart the mirrors, the greater the difference in seismic noise at each mirror.
E. The larger the interferometer, the more expensive it is.
Which merger produces an electromagnetic signal that astronomers can detect?
A. The merger of two black holes.
B. The merger of two neutron stars.
C. Both types of merger.
If a gravitational wave detector were built to detect mergers of supermassive black holes, how would it have to differ from the LIGO/Virgo detectors?
A. The LIGO/Virgo detectors are already able to detect mergers of supermassive black holes, but has not done so because supermassive mergers are rarer.
B. The detector arms should be much longer, because supermassive black holes are much larger, so generate longer wavelength waves.
C. The detector would have to be more sensitive, because merging supermassive black holes produce less powerful gravitational waves.
D. The detector would need to last a long time, because supermassive black hole binaries are detectable in gravitational waves long before they merge.
E. The detector should be built in space, to reduce the seismic noise.
You fire a rocket from Earth. Which rocket wins the orbital race (which rocket returns first to the starting point)?
A. The rocket that stays on Earth;
B. The rocket that fires forwards;
C. The rocket that fires outwards;
D. The rocket that fires backwards;
E. The rocket that fires inwards.

Wed 2019 Apr 24:
What in this room has the highest entropy (technically, is closest to thermodynamic equilibrium)?
A. Your brain.
B. Your blood.
C. The chairs and tables.
D. The image on the screen you are looking at.
E. The air.
The “no-hair” theorem states that an isolated black hole quickly evolves to a state characterized by what?
A. Space and time.
B. Energy and momentum.
C. Mass and radius.
D. Luminosity and temperature.
E. Mass, electric charge, and spin.
A more massive black hole produces Hawking radiation with longer wavelength. Therefore a more massive black hole produces Hawking radiation that is _____ energetic, and therefore has a _____ Hawking temperature.
A. Equally, equal.
B. Less, lower.
C. More, lower.
D. Less, higher.
E. More, higher.
Could the x-ray emission observed from x-ray binaries containing a black hole be Hawking radiation?
A. Yes.
B. No.
Mon 2019 Apr 29:
Would you vote in favor of making a baby Universe?
5 A. I think that it is immoral to attempt to make a baby Universe. I vote no.
16 B. If this is the only way that our Universe can reproduce, then I think society has a moral duty to make it happen. I vote yes.
7 C. I don't think society should waste resources attempting to make a baby Universe. I vote no.
47 D. I don't have a strong moral opinion, but I support the notion that society should attempt to make a baby Universe. I vote yes.
1 E. I don't really care either way. I probably won't bother to vote.
If society were presented with the one-time opportunity to make a baby Universe, what do you think the eventual outcome would be?
12 A. All out war between the yes and no factions.
21 B. Fierce political discussion, resolved by the democractic process.
34 C. Fierce political discussion, leading to deadlock.
8 D. Nothing. Society would not care, and would just go about its business.
You are the leader of the “No-baby-Universe” faction. You believe deeply that your cause is right. You strive for right. But your faction has lost the vote. What do you do?
10 A. Continue to argue non-violently for your cause.
46 B. Fight for right. Start a guerilla war.
16 C. Spread disinformation about your opponents and their theory of making baby Universes.
3 D. Something else.
How should the movie end?
18 A. As the science says: the people outside the black hole never know whether a baby Universe was made, or what might be the nature of that baby Universe.
14 B. The baby Universe should expand out into the old Universe, destroying it, and starting afresh.
25 C. Somehow there is an unexpected line of communication from inside the black hole to outside, that allows people outside the black hole to discover what happened.
15 D. Postpone the conclusion to a sequel.
3 E. Something else.
Wed 2019 May 1:
What aspects of these observations allows the mass of the black holes to be measured?
A. The brightness of the central region of the galaxy.
B. The velocity of the stars.
C. The size of the region containing the stars.
D. The combination of the stars' velocity and the size of the region containing them.
E. The fact that the velocity is constant at small radius.
What do astronomers consider to be the best current observational evidence for black holes?
A. Evidence for relativistic motion, such as superluminal jets.
B. Evidence for very high energy phenomena, such as quasars.
C. A lot of mass in a small space.
D. Gravitational waves.
E. Einstein's theory of general relativity predicts black holes, and keeps passing observational tests.

Black Hole silhouetted against the Milky Way Spring 2019 ASTR 2030 Homepage

Updated 2019 May 1