Astronomy 123 Midterm 2
To predict whether a star will ultimately become a black hole, what is the key property of the star we should look at? a. mass b. surface temperature c. color d. distance e. diameter
a. mass
A gravitational lens is formed by a. mass between the source and earth b. a lens the size of a galaxy c. mass behind the source d. gravitational waves e. light redshifted by a black hole
a. mass between the source and earth
Spacetime effects like time dilation are only noticeable when a. objects move close to the speed of light b. we have proper telescopes c. events in spacetime are connected by light beams d. very massive objects are involved e. we are near a black hole's event horizon
a. objects move close to the speed of light
When we determine the age of the universe using the Hubble Time (1/H0), what important simplifying assumption goes into our calculations? a. that the expansion of the universe has been happening at the same rate -neither speeding up or slowing down b. that all the galaxies are moving away from us at exactly the same speed, no matter how far away they are c. that the cosmological principle doesn't hold: the universe is not isotropic and homogeneous d. that we have accounted correctly for the effects of dark energy e. that the universe is actually contracting instead of expanding
a. that the expansion of the universe has been happening at the same rate -neither speeding up or slowing down
The speed that gravitational waves travel is a. the speed of light b. one half the speed of light c. the speed of sound in empty space d. dependent on the black hole mass e. twice the speed of light
a. the speed of light
Spacetime effects like time dilation are only noticeable when a.objects move close to the speed of light b.we have proper telescopes c.events in spacetime are connected by light beams d.very massive objects are involved e.we are near a black hole's event horizon
a.objects move close to the speed of light
Why did Einstein introduce the cosmological constant into the equations of his General Theory of Relativity when describing the universe? a. Einstein did not realize that black holes would exist at the centers of galaxies and pull everything into them b. Einstein's equations required the universe to expand or contract; he could not imagine or accept it doing either one, so he put a factor in to stop it from moving c. Einstein talked to Hubble and learned about Hubble's observations of the expanding universe, which made him so uncomfortable that he decided to change his equations d. Einstein had a hunch that the universe was accelerating (speeding up its expansion) back in 1918 and so introduced the constant into his equations to describe that e. Einstein liked cups of tea in the afternoon, and his constant was a comment on that habit
b. Einstein's equations required the universe to expand or contract; he could not imagine or accept it doing either one, so he put a factor in to stop it from moving
Einstein suggested that the regular change (advance) in the perihelion of the planet Mercury could be explained by: a. the presence of a planet inside the or bit of Mercury, whose gravity influenced Mercury b. a distortion in spacetime caused by the gravity of the Sun c. the pull of a small black hole that orbits our Sun so closely that we are not able to see it d. the presence of a strong magnetic field in the Sun, which causes huge outburst of material e. a distortion in our view of the solar system caused by the Earth's atmosphere
b. a distortion in spacetime caused by the gravity of the Sun
When laser beams in an interferometer combine a. the resulting light only gets brighter b. an interference pattern of bright and dark light is formed c. the resulting light travels at twice the speed of light d. the increased laser power melts the camera e. the photons are destroyed
b. an interference pattern of bright and dark light is formed
General Relativity predicts that light passing near a massive object like the sun will a. be spread into a spectrum of wavelengths b. appear bent when observed from Earth c. be the same as always d. make the sun's mass exceed 1.4 solar masses e. be reflected back
b. appear bent when observed from Earth
After travelling 140 million light years from the 170817 neutron star merger, gravitational waves and gamma rays a. annihilated each other to produce a gamma-ray burst b. arrived at earth at almost exactly the same time c. combined to produce heavy elements d. were assumed to have been produced, but were not observed e. arrived at earth 1.4 years apart
b. arrived at earth at almost exactly the same time
In our modern view of the expansion of the universe, we understand that it is space that is stretching; individual galaxies don't speed away from each other as if they were rockets. In that case, why do galaxies show a redshift? a. as galaxies age, they get redder and redder b. as space stretches, the waves of radiation in space also stretch and their wavelength increases c. as space stretches, the presence of dark matter slows down the light between galaxies d. as time go es on, waves in space encounter more and more dust, and get redder e. astronomers cannot think of any good explanation for the redshift if it's space that expands/stretches
b. as space stretches, the waves of radiation in space also stretch and their wavelength increases
The gravitational wave signal from merging black holes is called a "chirp" because a. birds mimicked the signal b. as the black holes get closer, the signal frequency and amplitude increase c. as the black holes get closer, the signal frequency and amplitude decrease d. as the black holes get closer, the signal frequency decreases and the amplitude increases e. after the merger, the final black hole produces a chirp-like signal
b. as the black holes get closer, the signal frequency and amplitude increase
Today, we believe that only a small number of elements were actually formed during the Big Bang. Which of the following was NOT one of these: a. hydrogen b. carbon c. lithium d. helium e. you can't fool me, all of the above were definitely formed during the big bang
b. carbon
The term "multi-messenger astronomy" refers to a. using both audio and video in the classroom b. combining electromagnetic and gravitational wave observations c. finding standard candles for measurements of the Hubble Law d. a misnomer for multi-messenger astrology e. none of the above
b. combining electromagnetic and gravitational wave observations
If the universe consisted only of matter and its density were equal to critical, the universe would a. continue expanding, then slow down and contract, ending in a "big crunch" b. continue expanding, eventually slowing down to zero c. continue expanding, eventually speeding up d. continue expanding at a reduced rate e. not expand at all
b. continue expanding, eventually slowing down to zero
Current measurements of the Hubble constant Ho a. all agree on a single value b. disagree depending on the method used c. all use Type Ia supernovae as standard candles d. indicate the universe will someday contract to a single point e. are meaningless
b. disagree depending on the method used
Based on many surveys of the average density of matter in the universe (regular matter and dark matter), astronomers now conclude that the average density of the universe is a. less than the critical density b. exactly equal to the critical density c. more than the critical density d. essentially equal to zero e. so great that the universe will experience a "big crunch" before the Sun becomes a red giant
b. exactly equal to the critical density
Evidence for dark matter in astronomy includes galactic rotation curves, interacting galaxy clusters like the "bullet cluster", and a. cosmic rays b.gravitational lensing by galaxy clusters c. neutrino emission d. detection by underground instruments e. collisions in particle accelerator experiments
b. gravitational lensing by galaxy clusters
Galaxies that we see as they were 11 billion years ago or more, as compared to galaxies today, are generally: a. bluer and smaller b. redder and smaller c. redder and larger d. bluer and larger e. pretty much the same
b. redder and smaller
When astronauts aboard the International Space Station (ISS) in space let go of an orange, it just floats there. Why is that? a. the ISS is so far from the Earth, the gravity there is essentially zero b. the ISS is falling around the Earth, and in free fall, things feel no weight c. spacetime is so different aboard the ISS, that time stops, and so nothing can fall d. the law of gravity only works on the Earth, it doesn't work in space e. this is an unsolved problem in science, and so it is "fruitless" to worry about it
b. the ISS is falling around the Earth, and in free fall, things feel no weight
The three pillars of evidence for big bang cosmology are the cosmological redshift, big bang nucleosynthesis, and a. dark matter b. the cosmic microwave background c. grand unification of forces d. the matter-antimatter asymmetry e. supersymmetry
b. the cosmic microwave background
Once a black hole forms, the size of its event horizon is determined only by a. the size (diameter) of the star that collapsed into the black hole b. the mass inside the event horizon c. the time since the black hole formed d. the composition of the material that formed the black hole e. none of the above -- every black hole has an event horizon of the same size
b. the mass inside the event horizon
Recent observations indicate that the universe is expanding faster today than it was a few billion years ago (that, in other words, the expansion of the universe is accelerating.) What kind of observations have led astronomers to this surprising conclusion? a. the measurements of cepheid variables in the galaxies of the Local Group b. the measurement of galaxy distances using Type Ia supernovae c. the discovery of large amounts of dark matter in the halo of the Milky Way d. the measurements of the amount of deuterium in the universe e. the fact that galaxies today are getting a lot more speeding tickets than they used to
b. the measurement of galaxy distances using Type Ia supernovae
The first time that astronomers observed both gravitational waves and electromagnetic waves from the same event, what they were observing was: a. a supernova explosion in one of the closest galaxies to us b. the spiraling toward each other of two neutron stars c. a binary star system where a giant st ar is overloading a white dwarf with too much material d. the merger of two black holes with masses dozens of times the mass of our Sun e. the collapse of an entire cluster of stars into one big black hole
b. the spiraling toward each other of two neutron stars
In the observation of galaxies, astronomers refer to look-back time, which means a. the glory days of astronomy b. the time it took for the observed light from a galaxy to reach us c. the current distance to a galaxy divided by c d. the time required to take a good spectral image of a galaxy e. Thursdays
b. the time it took for the observed light from a galaxy to reach us
The main postulate of special relativity is that a.the speed of gravity is zero b.the speed of light is an absolute constant c.cosmic rays should be able to reach the earth d.space and time should be discarded e.the speed of thought is nonexistent in LA 177
b.the speed of light is an absolute constant
A galaxy observed at redshift of z=9 has a prominent hydrogen spectral line. If this same spectral line has a wavelength of 100nanometer (nm) when observed from hydrogen in a lab on earth, its observed wavelength from the galaxy is a. 100 nm b. 500 nm c. 1000 nm d. 2000 nm e.1 millimeter
c. 1000 nm
At first, right after the Big Bang, the universe was too hot for nuclei and electrons to combine into the kinds of neutral atoms that are familiar to us today. How soon after the beginning did it become cool enough for neutral atoms to form? a. 10-43 seconds b. 3 minutes c. a few hundred thousand years d. a billion years e. only last Thursday
c. a few hundred thousand years
The object(s) created by the merger of two black holes is a. a neutron star b. a pair of black holes with slightly lower mass c. a single black hole with mass slightly lower than the sum of the merging ones d. a single black hole with mass equal to the sum of the merging ones e. a supernova
c. a single black hole with mass slightly lower than the sum of the merging ones
If you are in a freely falling elevator near the top of a tall building, as the elevator falls, your weight would be: a. the same as your usual weight b. a bit less than your usual weight c. equal to zero - you would be weightless d. a little more than your usual weight e. so great that you would be pressed to the floor and in great pain
c. equal to zero - you would be weightless
According to the Cosmological Principle, the universe a. has no beginning and no end b. cannot be understood by the use of scientific observations alone c. is isotropic and homogeneous d. consists only of galaxies that are exactly like the Milky Way e. has all the galaxies arranged in groups about the size of our Local Group
c. is isotropic and homogeneous
In describing the universe usin g his equations of general relativity, Einstein assumed that it was isotropic (the same in all directions.) What recent observations have confirmed that the universe is isotropic on the large scale? a. the discovery of pulsars b. the discovery of cannibal galaxies c. measurements of the cosmic microwave background radiation d. measurements of neutrinos from Supernova 1987A e. the discovery that there is really nothing very good on TV, no matter which way you point your dish (antenna)
c. measurements of the cosmic microwave background radiation
Merging black holes can be observed a. only at night b. by their radio wave emissions c. only by their gravitational wave emission d. by radio and gravitational wave emissions e. by their x-ray and gravitational wave emissions
c. only by their gravitational wave emission
The reciprocal of the Hubble constant (1/H0) is a rough measure of the: a. the period of a typical Cepheid variable b. the distance to the last galaxies that formed c. the age of the universe d. the luminosity of a type I supernova explosion e. the cost of building a telescope in space
c. the age of the universe
How do astronomers currently think the amount of detectable (observable) matter in the universe compares to the amount of dark matter and dark energy? a. the amount of detectable matter is about equal to the amount of dark matter & energy b. the amount of detectable matter is far greater than the amount of dark matter & energy c. the amount of detectable matter is far less than the amount of dark matter & energy d. the amount of detectable matter is about 1/10th the amount of dark matter & energy e. there is no evidence for dark matter anywhere, so this is not a topic astronomers can make any estimates about
c. the amount of detectable matter is far less than the amount of dark matter & energy
The equivalence principle (principle of equivalence) says that a. the amount of energy released by fusion is equivalent to the amount of mass that is lost b. gravity is equivalent the strong nuclear force is inside any nucleus c. the effects of gravity are equivalent to the effects of acceleration d. far away from a black hole, its pull is equivalent to the pull of the star that it formed from e. the event horizon of a black hole is equivalent to the place where things are forever trapped
c. the effects of gravity are equivalent to the effects of acceleration
An astronomer is observing a distant galaxy which looks blue. Which of the following can she conclude from this observation? a. the galaxy must be moving toward us (must have a blue shift) b. the galaxy must be extremely large (probably a giant elliptical) c. the galaxy must have a lot of star formation going on at the time we are seeing it d. the galaxy must be rotating very slowly or not at all e. the galaxy must contain only older stars (those that formed billions of years ago)
c. the galaxy must have a lot of star formation going on at the time we are seeing it
With enormous effort, a team of astronomers manages to collect enough light from a galaxy far, far away to produce a spectrum. That spectrum has lines from the elements carbon, silicon, and sulfur. This tells the team that a. the galaxy must be closer to us than 1 billion light years b. the galaxy must contain a quasar c. the galaxy must have had an entire generation of stars that was born, lived, and died d. the galaxy must be a massive elliptical galaxy e. what they are seeing is not a galaxy at all, but the remnant of one supernova
c. the galaxy must have had an entire generation of stars that was born, lived, and died
In the first direct detection of gravitational waves by LIGO in 2015, the waves came from a. the collapse of a nearby star into a white dwarf b. a supernova explosion in a nearby galaxy c. the merger of two black holes d. the rapid motion of three hot Jupiter planets around a nearby star e. the dashed hopes of all the people in the U.S. who want their government to work well for them
c. the merger of two black holes
In the first direct detection of gravitational waves by LIGO in 2015, the waves came from a. the collapse of a nearby star into a white dwarf b. a supernova explosion in a nearby galaxy c. the merger of two black holes d. the rapid motion of three hot Jupiter planets around a nearby star e. the dashed hopes of all the people in the U.S. who want their government to work well for them
c. the merger of two black holes
The elementary particles making up ordinary matter on earth today are a. up quark, down quark, top quark b. up quark, neutrino, gluon c. up quark, down quark, electron d. electron, proton, neutrino e. electron, positron, neutrino
c. up quark, down quark, electron
Special relativity gives a "speed limit", meaning that a.time slows down in rockets b. elliptical galaxies have smaller redshifts c.objects cannot move faster than the speed of light d. vehicles in Bern, Switzerland move too fast e. Einstein did not watch Star Trek
c.objects cannot move faster than the speed of light
After the Big Bang, in order for the universe to become transparent to light and other electromagnetic radiation, what had to happen? a. stars and galaxies had to form b. the whole universe had to be hotter than the interior of a star c.the universe had to cool enough to allow neutral hydrogen to form d. the dark energy had to dominate over regular matter and energy e. telescopes had to be invented
c.the universe had to cool enough to allow neutral hydrogen to form
Roughly what percent of the mass and energy contents of the universe is made up of dark matter plus dark energy? a. 5 percent b. 10 percent c. 50 percent d. 95 percent e. astronomers have no way of estimating this percentage
d. 95 percent
Which of the following is not a candidate for the identity of dark matter: a. primordial black holes b.weakly interacting elementary particles c. anti-matter d. MACHOs e. we now know there is no dark matter
d. MACHOs
Having two LIGO detectors separated by 3000 km is important because a. only true astrophysical signals would be observed in both detectors b. chirping signals can only be observed by two or more detectors c. the time of arrival of signals can be used to find the position of the sources d. a & c e. none of the above
d. a & c
Factoring in everything we currently know about the history of the universe, our best estimate for the age of the universe is a. 4.6 billion years b. about 100 billion years c. roughly 2 million years d. about 13.8 billion years e. the age of the universe is infinite; there was no beginning
d. about 13.8 billion years
According to the general theory of relativity, the presence of mass a. causes motion at the speed of light squared b. is equivalent to the presence of light c. causes curved paths to straighten out until they are exactly straight lines d. causes a curvature (or warping) of spacetime e. will cause a black hole to form, unless there is motion
d. causes a curvature (or warping) of spacetime
Measurements of the cosmic microwave background provide strong evidence that the overall geometry of space is a. trapezoidal b. spherical, or positive curvature c. hyperbolic, or negative curvature d. flat, or zero curvature e. circular
d. flat, or zero curvature
When one member of a binary star system is a black hole, and astronomers detect flickering x-rays coming from the system, where are these x-rays usually coming from? a. from inside the black hole event horizon b. from the photosphere of the companion star (the star that is not a black hole) c. from the singularity d. from a disk of material around the black hole (material that has been pulled from the companion star and is falling toward the black hole) e. from a distant galaxy that just happens to lie behind the black hole system (astronomers discovered that such x-rays have nothing to do with the black hole)
d. from a disk of material around the black hole (material that has been pulled from the companion star and is falling toward the black hole)
What do the surveys of the three -dimensional distribution of groups of galaxies reveal about how groups and clusters of galaxies are organized? a. galaxy groups are distributed completely evenly--there is typically the same amount of space between them--and so there is no structure evident b. galaxy groups make a huge spiral structure that resembles the Milky Way (but is much bigger) c. galaxy groups are organized into huge spherical "lumps" with concentric rings of groups of galaxies around each lump d. galaxy groups are organized into huge filaments with great voids between them--something like the structure one would see taking a cross - section of some soap bubbles e. you can't fool me; astronomers cannot get any sense with our present - day instruments of how groups of galaxies are distributed on the large scale
d. galaxy groups are organized into huge filaments with great voids between them--something like the structure one would see taking a cross-section of some soap bubbles
What is a key reason that gravitational waves are so much harder to detect than electromagnetic (e-m) waves? a. gravitational waves don't create any kind of disturbance the way e-m waves do b. gravitational waves are so strong, they really shake our detectors, making measurements difficult c. gravitational waves get all mixed up with sound waves in the Earth's atmosphere, and are therefore hard to distinguish from all the sound d. gravitational waves are much weaker than e-m waves, and therefore require very, very precise equipment to detect e. because the GW scientists are incompetent
d. gravitational waves are much weaker than e-m waves, and therefore require very, very precise equipment to detect
The most prolifically created nuclear species in big bang nucleosynthesis is a. hydrogen, H b. deuterium,2H c. helium 3,3He d. helium 4,4He e. carbon 12,12C
d. helium 4,4He
If we want to see what galaxies looked like at a time close to the beginning of the universe, where should we look? a. in the Local Group of galaxies b. within the nearest 100 million light years from the Milky Way c. near the center of the Virgo Cluster of galaxies d. in a direction away from the plane of the Milky Way, where we can see very faint galaxies that are more than 10 billion light years away e. it doesn't matter; you can look at any galaxy, because all galaxies look pretty much the same today as they did in the early days of the universe
d. in a direction away from the plane of the Milky Way, where we can see very faint galaxies that are more than 10 billion light years away
Which of the following does NOT happen when two galaxies collide? a. large interstellar gas clouds collide b. the rate of star formation increases c. the shape of the galaxy is often changed d. many of the stars in one galaxy collide with the stars in the other e. a smaller galaxy may wind up inside a larger one
d. many of the stars in one galaxy collide with the stars in the other
We now know that most heavy elements such as gold are produced in a. factories in China b. supernova explosions of massive stars c. black hole mergers d. neutron star mergers e. white dwarf mergers
d. neutron star mergers
The three pillars of evidence for big bang cosmology are the cosmological redshift, the cosmic microwave background, and a.dark matter b. the matter-antimatter asymmetry c. grand unification of forces d. nucleosynthesis e. supersymmetry
d. nucleosynthesis
The red and blue spots in images of the cosmic microwave background images represent a. creation of heliumnuclei b. regions of extremely large over-density and under-density c. regions of star formation d. regions of small over-density and under-density e. regions where antimatter dominates
d. regions of small over-density and under-density
The region around a black hole where everything is trapped, and nothing can get out to interact with the rest of the universe, is called a. the singularity b. the neutron star radius c. the gravitational redshift zone d. the event horizon e. day-time television
d. the event horizon
The redshift observed in the light emitted by distant galaxies is due to a. the Doppler shift of the galaxies moving away from us through a fixed space b. the Doppler shift of the galaxies moving towards us through a fixed space c. the gravitational redshift of the galaxies' immense mass d. the expansion of space e. radio-bright quasars
d. the expansion of space
The location of the 170817 neutron star merger was first determined using a. radio telescopes b. texts by ancient Chinese astronomers c. the iterative guess method d. three gravitational wave detectors e. the earth's rotation
d. three gravitational wave detectors
In the 2015 gravitational wave discovery event, the two black holes a. were supermassive b. combined to form a neutron star c. were each about 1 solar mass d. were each about 30 solar masses e. never merged
d. were each about 30 solar masses
Time dilation means that a.cosmic rays cannot hit the earth b.we cannot determine time in moving reference frames c. the closer a star is to the center of the galaxy, the longer it will take to go around d.moving clocks run slow e. you need your eyes examined
d.moving clocks run slow
The 170817 event demonstrated that neutron star mergers a. produce gamma ray bursts b. produce gravitational waves c. produce most of the heavy elements on earth d. produce kilonova afterglows e. all of the above
e. all of the above
The core of neutron stars consists of a. a hot, dense gas b. neutrons c. a mix of nuclear matter d. a quark-gluon plasma e. matter with super-nuclear density in a form we don't know for sure
e. matter with super-nuclear density in a form we don't know for sure
A student shines a flashlight out the window of a very fast rocket. If the normal speed of light is c, then a. if she shines it forward, the light travels a bit faster than c b. if she shines it backwards, the light travels a bit slower than c c. if she shines it forward, the light travels a bit slower than c d. if she shines it backwards, the light travels a bit faster than c e. the light always travels at speed c
e. the light always travels at speed c
