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CHAPTERS COVERED POST MIDTERMS Flashcards

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1
Q

You wish to observe a galaxy like the Milky Way, but in its infancy. Where do you look?

A

Very far away. We get an image of galaxies as they were billions of years ago, and so cans many young galaxies

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2
Q

The early University contained a roughly uniform distribution of hydrogen and helium, with small pockets of higher density. Where would you expect galaxies to form?

A

In the regions of higher density

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3
Q

Which of the following is most likely to produce an elliptical galaxy?

A

A dense protogalactic cloud with almost no angular momentum

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4
Q

Why are distant galaxies often irregular in shape?

A

The early Universe was crowded, so regular galaxies collided to produce irregular ones more often

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5
Q

Which of the following is not a valid reason for why a galaxy may contain only very few young stars?

A

Short-lived stars are not produced by starbursts

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6
Q

What is a quasar?

A

A “quasi-stellar radio source”, a powerful accretion disk around a supermassive black hole

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7
Q

The edges of the accretion disk near the AGN nucleus

A

The glow of intergalactic gas stimulated by the jets of an AGN

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8
Q

About how many new stars are born in the Milky Way in one Earth year?

A

1-10

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9
Q

An X-ray source triples in luminosity over the course of a day. What can we conclude about the source?

A

It must be smaller than a light day across

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10
Q

About how many new stars are born in a starburst galaxy in one Earth year?

A

100

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11
Q

Why would it be a bad idea to shake hands with the antimatter version of yourself?

A

You would both annihilate and convert to photons

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12
Q

You are AU from a neutron star. Which force do you feel the most?

A

gravity

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13
Q

Which of the following places the eras in order of ascending time (or descending temperature)?

A

GUT, electroweak, particle, nucleosynthesis, nuclei, atoms

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14
Q

Why do we think that CMB came from the era of atoms?

A

This is when photons were first allowed to freely propagate

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15
Q

What was the approximate temperature of the Universe when the CMBR was emitted

A

3000K

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16
Q

How can inflation help explain the large-scale uniformity of the Universe today?

A

It allowed for thermal equilibration between objects that are no longer in the same observable Universe

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17
Q

If the Universe are infinite and fairly evenly distributed with stars, but didn’t have a Big Bang at the beginning (i.e. it was a “static universe”, what would the night sky look like?

A

Completely bright

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18
Q

Which of the following observations led to the idea of dark matter?

A

Galaxies were found to be more massive than their luminosities would suggest

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19
Q

Which of the following observations led to the idea of dark energy?

A

The Universe’s expansion was too fast to be explained through known physics

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20
Q

Why do we call dark matter “dark”?

A

It does not seem to emit nor absorb electromagnetic radiation

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21
Q

Suppose we made a rotation curve for the moons of Jupiter. Which of the following would best describe this plot?

A

A falling curve

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22
Q

Why do we use the motion of atomic hydrogen gas clouds to gauge the masses of distant spiral galaxies?

A

They can be found far from the galactic center

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23
Q

What would allow you to estimate the total mass of a galactic cluster?

A
  • the velocities of individual galaxies within the cluster
  • the temperature of the intro-cluster medium
  • gravitational lensing of background galaxies
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24
Q

What would be a plausible way to observe a MACHO?

A

Monitor a distance star for lensing events

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25
What would be a plausible way to observe a WIMP?
- monitor a distant star for lensing events - look into the galactic halo for their visible light output - spot them on the outskirts of distant galaxies
26
Which of the following describes our Universe, in terms of expansion?
accelerating
27
What best represents the ratio of dar matter to regular matter in the Milky Way, in terms of mass?
10:1
28
You are a WIMP. Now, before you go filing complaints to the University administration about me insulting you, please remember that a WIMP is a Weakly Interacting Massive Particle. Which of the following pairs of forces will you certainly not feel?
electromagnetic and strong
29
Which of the following list the energy components of the Universe from largest amount to smallest amount?
dark energy, dark matter, regular matter
30
What is the earliest time from which we have evidence for life on Earth?
3.85 billion years ago
31
What is a stromatolite?
A kind of rock
32
What is the panspermia hypothesis?
The idea that life originated to outer space before landing on the surface of Earth
33
What is not a requirement for life on Earth?
Oxygen
34
The Martian meteorite ALH84001 found in Antarctica was a source of excitement for what reason?
It contained evidence that life might have existed on Mars
35
What life-bearing environment on Earth is most similar to where there might be life on the ice-bound Jovian moon Europa?
Deep-sea vent
36
What is not a concern when considering whether or not planets around other stars may be able to support life?
The number of planets orbiting the star
37
How has Jupiter helped obtect life on Earth (i.e. Why is Jupiter Earth's big brother)?
By gravitationally beating up many of the objects that may have collided with us
38
What type of electromagnetic radiation does the majority of SETI use?
radio
39
Assuming there was a spaceship that could travel at close to the speed of light, what relativistic shenanigans would interstellar astronauts have to deal with?
Time would pass differently for them than for people on planets
40
How do we observe the life histories of galaxies?
Deep observations of the universe show us the gistory of galaxies because we are seeing galaxies as they were at different ages
41
How do we study galaxy formation?
Our best models for galaxy formation assume that gravity made galaxies out of regions in the early universe that were slightly denser than their surroundings
42
Why do galaxies differ?
Some of the differences between galaxies may arise from the conditions in their protogalactic clouds (e.g. competition between angular momentum and mass density) Collisions can play a major role because they can transform two spiral galxies into an elliptical galaxy, or they can induce spiral arms
43
What are starburts?
A starburst galaxy is transforming its gas into stars much more rapidly than a normal galaxy. Starburst epochs likely last only a few million to a few ten million years
44
What are quasars?
Active galactic nuclei are very bright objects seen in the centers of some galaxies, and quasars are the most luminous type
45
What is the power source for quarsars and other active galactic nuclei?
The only moel that adequately explains the observations holds that the central engines (or power sources) of AGNs consist of mass falling into supermassive black holes
46
Do supermassive black holes really exist?
Observations of stars and gas clouds orbiting at the centers of galaxies indicate that many galaxies, and perhaps all of them, have suprmassive black holes
47
How do quasars let us study gas between the galaxies?
Absporption lines in the spectra of quasars tell us about intergalactic clouds between those quasars and Earth
48
What were conditions like in the early universe?
The early universe was so hot and so dense that radiation ws constantly producing particle-antiparitcle pairs and vise versa
49
How did the early universe change with time?
As the universe cooled, particle production stopped, leaving matter instead of antimatter Fusion turned remaining neutrons into helium Radiation traveled freely after formation of atoms
50
How do observations of the cosmic microwave background support the Big Bang theory?
Radiation left over from the Big Bang is now in the form of microwaves - the cosmic microwave background - which we can observe with a radio telescope
51
How do the abundances of elements support the Big Bang theory?
Observations of helium and other light elements agree with the predictions for fusion in the Big Bang theory
52
What key features of the universwe are explained by inflation?
The origin of structure, the smoothness of the universe on large scales, the nearly critical density of the universe Structure comes from inflated quantum ribbles Observable universe became smooth before inflation, when it was very tiny Inflation flattened the curvature of space, bringing expansion rate into balance with the overall density of mass-energy
53
Did inflation really occur?
We can compare the structures we see in detailed observations of the mocrowave background with predictions for the "seeds" that should have been planted by inflation So far, our observations of the universe agree well with models in which inflation planted the "seeds"
54
Why is the darkness of the night sky evidence for the Big Bang?
If the universe were eternal, unchanging, and everywhere the same, the enture night sky would be covered with stars The night sky is dark because we can see back to a time when there were no stars Stated more scientifically: The night sky is dark because we can only see a finite part in a universe of finite age - there is a horizon in a universe of the finite age. Furthermore, the light of distant stars is redshifted beyond visibility due to the expansion of the universe
55
What do we mean by dark matter and dark energy?
Dark matter is the name given to not "directly" visible mass whose gravity governs the observed motions of stars and gas clouds Dark energy is the name given to whatever might be causing the expansion of the universe to accelerate
56
What would you conclude about a galaxy whose rotational velocity rises steadily with distance beyond the visible part of its disk?
It's especially rich in dark matter
57
What kind of measurement does not tell us the mass of a cluster of galaxies?
Measuring the total mass of cluster's stars
58
What is the evidence for dark matter in galaxies?
Rotation curves of galaxies are flat, indicating the most of their matter lies outside their visible regions
59
What is the evidence for dark matter in clusters of galaxies?
Masses measured from galaxy motions, temperature of hot gas, and gravitational lensing all indicate that the vast majority of matter in clusters is dark
60
Does dark matter really exist?
Either dark matter exists or our understanding of gravity must be revised
61
What might dark matter be made of?
There does not seem to be enough normal (baryonic) matter to account for all the dark matter, so most astronomers and physicists suspect that dark matter is made of (non-baryonic) particles that have not yet been observed in particle physics labs
62
What is the role of dark matter in galaxy formation?
The gravity of dark matter seems to be what drew gas together into protogalactic clouds, initiating the process of galaxy formation WIMP dark matter can also start to form clumps before ordinary matter could form clumps
63
What are the largest structures in the universe?
Galaxies appear to be distributed in gigantic chains and sheets that surround great voids The largest confirmed structures (like the Sloan Great Wall) have a size of order of a billion light years, and likely there are no larger structures than that (the astronomical "End of Greatness")
64
Suppose that the universe has more dark matter than we think there is today. How would this change the age we estimate from the expansion rate?
The estimated age would be smaller
65
Will the universe continue to expand forever?
Current measurements indicate that there is not enough dark matter to prevent the universe from expanding forever
66
Is the expansion of the universe accelerating?
An accelerating universe is the best explanation for the distance we measure when using white dwarf supernovae as standard candles A large amount of uniformly distributed energy (about 69% of the total energy density in the universe) can explain the observed acceleration of cosmic expansion. This uniformly distributed form of energy is denoted as Dark Energy
67
When did life arise on Earth?
Life arose at least 3.85 billion years ago, shortly after end of heavy bombardment
68
How did life arise on Earth?
Life evolved from a common organism through natural selection, but we do not yet know the origin of the first organism
69
What are the necessities of life?
Nutrients, energy, and liquid water
70
Could there be life on Mars?
Evidence for liquid water in past suggests that life was once possible on Mars
71
Could there be life on Europa or other jovian moons?
Jovian moons are cold but some show evidence for subsurface water and other liquids
72
What kinds of stars might have habitable planets?
Billions of stars have sizeable habitable zones, but we don't yet know how many have terrestrial planets in those zones
73
Are Earth-like planets rare or common?
We don't yet know because we are still trying to understand all the factors that make Earth suitable for life
74
How many civilizations are out there?
We don't know, but the Drake equation gives us a framework for thinking about the question
75
How does SETI work?
Some telescopes are looking for deliberate communications from other worlds
76
How difficult is interstellar travel?
Interstellar travel remains well beyond our current capabilities and poses enormous difficulties
77
Where are the aliens?
Some people suggest that if interstellar civilizations are common then at least one of them should have colonized the rest of the galaxy Are we alone? Has there been no colonization? Are the colonists hiding? We don't know yet

ASTRONOMY (3 decks)

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