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astrology > pollev questions > Flashcards

pollev questions Flashcards

1
Q

There is a limit to how much electron degeneracy pressure a star can have. This leads to…
A. a maximum mass for a main sequence star of 150Msun
B. a maximum mass for a neutron star of 10Msun
C. a maximum mass for a white dwarf of 1.4Msun
D. a maximum mass for a red giant star of 2Msun

A

C

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2
Q

Which of the following objects has the smallest radius?
A. 1.0Msun main sequence star
B. 1.1Msun star undergoing hydrogen shell fusion
C. 1.2 Msun white dwarf
D. 1.3Msun neutron star

A

D

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3
Q

Assuming that Sirius A (main sequence) and Sirius B (white dwarf) were born at the same time, which star would you expect is more massive?
A. Sirius A
B. Sirius B
C. you can’t tell, because white dwarfs cool on the H-R diagram
D. you can’t tell, for some other reason

A

B

more massive stars evolve off the main sequence faster.
however, keep in mind it ejected mass during the planetary nebula phase

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4
Q

What happens to a white dwarf if it accretes material from a binary companion and reaches the white dwarf limit of 1.4Msun?
A. explodes as a white dwarf supernova
B. explodes as a massive star supernova
C. splits apart into two white dwarfs
D. nothing, accretion just stops

A

A

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5
Q

How does an isolated white dwarf produce light?
A. nuclear fusion of hydrogen on its surface
B. nuclear fusion of carbon in its core
C. accretion of material from a companion star
D. thermal radiation from its leftover heat

A

D

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6
Q

Supernova 1987A emitted neutrinos that signified the formation of a neutron star; but when we look there today, we don’t see a pulsar. What can you conclude?
A. it must have collapsed into a black hole
B. it could still have left behind a neutron star
C. it must have been a white dwarf supernova, not a massive star supernova
D. the neutrinos must have been emitted by some other mechanism

A

B
the pulsar beam might just never point towards earth

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7
Q

X-ray bursts from neutron stars have a similar origin as __________ from white dwarfs
A. novae
B. supernovae
C. electron degeneracy pressure
D. black holes

A

A
a result of accretion, and does not cause the destruction of the original star

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8
Q

If the sun suddenly collapsed to become a black hole (without changing its mass), what would happen to Earth’s orbit?
A. quickly fall into black hole
B. keep orbiting as it currently does
C. fly off in a straight line with a constant speed
D. spiral in to the black hole to make an accretion disk

A

B

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9
Q

Which occurs near the event horizon of a black hole?
A. time slows down
B. light appears redshifted
C. the sum of the angles in a triangle is not equal to 180 degrees
D. all of the above

A

D

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10
Q

Imagine the sun shrunk to a radius of just a few km, but kept all of its mass.
What would happen to the escape velocity from its surface (compared to now)?
A. stay the same
B. decrease
C. increase
D. not possible to tell

A

C

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11
Q

What happens to the radius of the event horizon as material falls into a black hole?
A. increases
B. decreases
C. doesn’t change
D. material can’t fall in

A

A

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12
Q

Einstein’s Theory of Relativity describes gravity as…
A. a force that acts instantly between two massive objects
B. a force carried by photons at the speed of light
C. a distortion of 3D space
D. a distortion of 4D spacetime

A

D

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13
Q

What happens when a neutron star’s mass exceed 3Msun?
A. neutrons split into protons and electrons
B. it exceeds the Scharzschild radius for its mass
C. it collapses down to a black hole
D. B and C

A

C

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14
Q

Where do we have strong evidence for the presence of a black hole?
A. center of the sun
B. center of the Milky Way
C. in all X-ray binary star systems
D. nowhere

A

B

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15
Q

How do we measure the mass of a black hole in an X-ray binary system?
A. orbital period and velocities inferred from the Doppler shift
B. luminosity and temperature of the companion star
C. time between X-ray pulses
D. black holes cannot be in X-ray binary systems, because no light can escape from a black hole

A

A

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16
Q

Which kind of main-sequence star is most likely to be part of the spheroidal population of the Milky Way?
A. A
B. B
C. M
D. O

A

C

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17
Q

William Herschel tried to locate the center of the Milky Way by counting the number of stars in different directions. This didn’t work because…
A. stars are not uniformly distributed
B. more distant stars are obscured by interstellar dust and gas
C. most of the stars are in the halo
D. there are very few stars near the galactic center

A

B

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18
Q

Rank the parts of the Milky Way from youngest to oldest: bulge; halo; disk; spiral arms

A

spiral arms < disk < bulge < halo

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19
Q

What differentiates a star in the Milky Way disk from a star in the Milky Way halo?
A. disk stars have more heavy elements
B. disk stars are younger
C. disk stars travel in organized orbits
D. all of the above

A

D

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20
Q

Which of the following best describes how globular clusters are distributed in the Milky Way?
A. spherically about the center of the galaxy in the halo
B. in a ring around the center of the galaxy
C. only in the spiral arms
D. distributed around the center in the disk

A

A

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21
Q

What is the likely result of the merger of two large spiral galaxies?
A. elliptical galaxy
B. small irregular galaxy
C. larger spiral galaxy
D. two galaxies of different types

A

A

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22
Q

Why does ongoing star formation lead to a blue-white appearance for the disk of a spiral galaxy?
A. the blue stars in the disk outshine other stars
B. there aren’t any red or yellow stars in the disk
C. there are a lot more blue stars than red or yellow stars in the disk
D. gas and dust in the disk absorbs all the blue light

A

A

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23
Q

What is likely to happen when two galaxies collide?
A. their stars will crash into each other
B. their shapes will be distorted by mutual gravity
C. their stars will evolve off the main sequence faster
D. nothing; they will go right through each other

A

B

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24
Q

Which of the following is a difference between elliptical and spiral galaxies?
A. on average, elliptical galaxies have bluer stars
B. stars in an elliptical galaxy all revolve around in the same direction
C. elliptical galaxies form new stars at a higher rate
D. large elliptical galaxies are more often found near the centers of galaxy clusters

A

D

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25
Q

Compared to elliptical galaxies, spiral galaxies have more…
A. gas
B. dust
C. young stars
D. all of the above

A

D

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26
Q

Edwin Hubble showed that distant galaxies are moving __________ us, with their __________ proportional to their ____________.
A. toward; brightness; distance
B. toward; speed; luminosity
C. away from; speed; distance
D. away from; distance; luminosity

A

C

27
Q

You observe a nearby star. When should you observe it again to see the largest parallax shift?
A. 3 months later
B. 6 months later
C. 9 months later
D. 12 months later

A

B

28
Q

You observe two Cepheid variable stars: Cepheid 1 has a period of 10 days, and appears brighter than Cepheid 2, which has a period of 20 days. Which can you infer?
A. 1 is farther away than 2
B. 2 is farther away than 1
C. 1 has a higher luminosity than 2
D. 2 has a higher luminosity than 1

A

B
2 has a higher luminosity but appears less bright, so it must be farther

29
Q

Why do white dwarf supernovae make better standard candles than massive star supernovae?
A. white dwarfs are brighter than massive stars
B. white dwarf supernovae come from binary systems, while massive star supernovae come from single stars
C. white dwarf supernovae are all nearly the same luminosity, because they explode when a white dwarf reaches the 1.4Msun limit
D. massive star supernovae only occur in elliptical galaxies

A

C

30
Q

A distant galaxy emits an infrared photon towards Earth. When the photon reaches Earth, it might be…
A. an X-ray photon
B. an ultraviolet photon
C. a red, visible light photon
D. a microwave photon

A

D

31
Q

Hubble’s law is V=H_0*d
If Hubble’s constant is 22km/sec per million light years, how fast is a galaxy moving away from us if it is at a distance of 100 million light years?

A. 22 km/s
B. 220 km/s
C. 2200 km/s
D. 22000 km/s

A

C

32
Q

Which of the following is the best standard candle to measure distances to galaxies that are billions of light-years away?
A. main sequence stars
B. a cepheid variable star
C. a white dwarf supernova
D. a massive star supernova

A

C

decent standard candles are B or C (because it’s possible to figure out their luminosity); for something this far away, you would want the additional apparent brightness of a supernova

33
Q

You observe a galaxy moving away from you at a speed of 0.1 light-years per year.
If this galaxy is 1.4 billion light-years away, how long has it taken to get there? (assume a constant rate of expansion)
A. 140 million years
B. 1.4 billion years
C. 14 billion years
D. 140 billion years

A

C

34
Q

Most of the light emitted by stars is in the visible part of the spectrum. If we wanted to observe the starlight from the very first galaxies, at what wavelength should we observe?
A. infrared
B. optical
C. ultraviolet
D. X-rays

A

A

35
Q

1km is 3.2e-20 Mpc. If the Hubble constant is 70km/s/Mpc, how old is the universe?

A

15 billion years

36
Q

What is the electric charge of an anti-electron?
A. negative
B. positive
C. neutral
D. the charge can vary

A

positive

37
Q

What are the eras of the universe, from earliest to latest?

A

Planck, GUT, electroweak, particle, nucleosynthesis, nuclei, atoms, galaxies

38
Q

As the universe transitioned through its different eras, what was happening?
A. the four fundamental forces were growing more similar
B. amount of antimatter in the universe was increasing
C. mass density of the universe was increasing
D. temperature of the universe was decreasing

A

D

39
Q

Which of the following is a prediction of the Big Bang Theory?
A. abundance of helium relative to hydrogen in the universe
B. 3000K background thermal radiation filling the universe today
C. galaxies are rushing away from a single point in space
D. matter and antimatter should be equally common in the universe

A

A

40
Q

Which of these abundance patterns is an unrealistic chemical composition for a star?
A. 70% H, 28% He, 2% other
B. 95% H, 5% He, <0.02% other
C. 75% H, 25% He, <0.02% other
B. 72% H, 27% He, 1% other

A

B

41
Q
A
42
Q

The cosmic background radiation has been mapped in detail. What does it look like?
A. it is all over the sky, and seen even where there is no matter
B. it is very uniform in its overall distribution
C. if you look very closely, there are slight variations from place to place
D. all of the above

A

D

43
Q

What is the temperature of the CMB?
A. 0K
B. 3K
C. 270K
D. 273K

A

B

44
Q

Which of the following is false?
A. universe may have inflated because of a strange vacuum energy
B. universe is uniform on large scales because before inflation, parts of universe were in equilibrium
C. universe started off in very hot state and has inflated exponentially since
D. according to inflation theory, universe is very much larger than the parts we currently see
E. during inflation, speed of expansion of space can exceed speed of light

A

C

45
Q

Why can’t we observe light from a time earlier than the beginning of the era of atoms?
A. there were no galaxies then
B. the light has redshifted too much to be detected today
C. photons from previous eras got absorbed and scattered by matter
D. our telescopes are made of atoms

A

C

46
Q

The idea of cosmic inflation explains…
A. the temperature of the CMB at the beginning of the era of atoms
B. the abundance of helium in the universe
C. the overall uniformity and amplitude of fluctuations in the CMB
D. the slight excess of matter over antimatter in the universe

A

C

47
Q

Geometry of the universe is most closely related to what other property of the universe?
A. total density of matter and energy
B. strength of strong nuclear force
C. mass of electron
D. temperature of CMB

A

A

48
Q

Why does cosmic inflation predict a flat geometry for the universe today?
A. inflation can only start in a flat universe
B. inflation implies the observable universe is a small fraction of the overall universe, so it should look flat on the scales we can observe
C. inflation predicts a total density of matter and energy for the universe to be much lower than the critical density
D. inflation predicts a total density of matter and energy for the universe to be much higher than the critical density

A

B

49
Q

Dark matter is inferred to exist because…
A. the Milky Way is full of dark patches
B. we observe its gravitational effects on visible matter
C. it causes the expansion of the universe to speed up
D. without it the CMB wouldn’t exist

A

B

50
Q

Approximately what fraction of the Milky Way’s mass is dark matter?

A

90%

51
Q

Which of the following is NOT a good way to measure the total mass of a cluster of galaxies?
A. add up the total mass of all the stars in the galaxies in the cluster
B. measure the speeds of the galaxies as they move around in the cluster
C. measure the temperature of the hot X-ray emitting gas in the cluster
D. observe the gravitational lensing of galaxies behind the cluster

A

A

52
Q

Which is NOT evidence for dark matter?
A. galaxies in clusters are moving faster than they should be
B. X-ray emitting gas in galaxy clusters is hotter than it should be
C. stars and gas in the outer parts of spiral galaxies are orbiting slower than they should be
D. gravitational bending of light by galaxies and clusters is stronger than it should be

A

C

53
Q

Which of the following explains the fluctuations seen in the CMB?
A. some parts of the universe were at a slightly higher temperature than others at the time when the CMB was formed
B. some parts of the universe were at a slightly higher density than others at the time when the CMB was formed
C. inflation expands the size of quantum fluctuations in the early universe to the size of the fluctuations seen in the CMB
D. all of the above

A

D

54
Q

Which region in the early universe was most likely to become a galaxy?
A. slightly higher density than average
B. exactly average density
C. slightly lower density than average
D. made of antimatter

A

A

55
Q

Evidence for accelerating expansion of the universe comes from observations of…
A. spiral galaxy rotation curves
B. X-ray emitting gas in galaxy clusters
C. cepheid variable stars
D. white dwarf supernovae

A

D

56
Q

How would a higher density of dark matter affect our estimate of the age of the universe?
A. implies an older universe
B. doesn’t affect inferred age
C. implies a younger universe
D. means expansion speeds up over time

A

C
higher density of dark matter would mean that expansion was originally faster than we believed, so universe would not have to be as old to be this expanded

57
Q

A universe with more dark matter is younger.

A universe with more dark energy is…

A. younger
B. the same age
C. older

A

C

58
Q

As far as we know, will the universe expand forever?

A. no, because the density may be slightly greater than the critical density
B. yes, because there is not enough dark matter to stop the expansion
C. yes, because dark energy causes the expansion to go faster and faster
D. yes, because of both B and C

A

D

59
Q

What is the PRIMARY evidence for the Big Bang?
A. expansion of the universe
B. CMB
C. abundance of helium and other light elements
D. all of the above

A

C

60
Q

What kind of galaxies are commonly found in galaxy clusters, contain little cool gas, and are not forming new stars?
A. elliptical
B. irregular
C. Local Group
D. spiral

A

A

61
Q

Which type of galaxy most often has a reddish-yellow appearance?

A

Elliptical

62
Q

Stars in the outer part of a spiral galaxy’s disk orbit…
A. much faster than stars near the center
B. much slower
C. about the same speed
D. in the opposite direction

A

C

63
Q

What is the expansion pattern of a universe where the matter density is more than the critical density, and there is no dark energy?
A. coasting
B. accelerating
C. recollapsing
D. critical

A

C

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