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Visions of the Universe > Final > Flashcards

Final Flashcards

1
Q

Which of these forms of radiation passes most easily through the disc of the Milky Way?

A

Infrared light

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2
Q

How do we determine the Milky Way’s mass outside the Sun’s orbit?

A

from the orbits of stars and gas clouds orbiting the galactic center at greater distances than the Sun

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3
Q

How old are most globular clusters?

A

12-13 billion years

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4
Q

What type of cluster is more abundant of heavy elements?

A

open clusters because they are younger

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5
Q

What is the halo?

A

covers the whole galaxy but is barely seen except for a few bright stars

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6
Q

Where are globular clusters located?

A

Not in the disk or bulge

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7
Q

Where does active star formation occur in galaxies?

A

in the disc

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8
Q

What are the differences between the disc and the halo?

A

Clusters of young stars are found only in the disk.
Gas and dust are abundant in the disk but not in the halo.
Stars in the disk all orbit in the same direction and nearly the same plane, while halo stars have more randomly oriented orbits.
Disk stars come in a broad range of masses and colors, while halo stars are mostly of low mass and red.

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9
Q

How does the diameter of the disk of the Milky Way compare to its thickness?

A

Diameter is 100x greater than the thickness

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10
Q

What do we call the bright, sphere-shaped region of stars that occupies the central few thousand light-years of the Milky Way Galaxy?

A

the bulge

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11
Q

Where is the Sun located in the Milky Way?

A

in the galactic disk, roughly halfway between the center and the outer edge of the disk

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12
Q

What do we mean by the interstellar medium?

A

the gas and dust that lies in between the stars in the milky way

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13
Q

What are the Magellanic Clouds?

A

2 small galaxies that orbit the Milky Way

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14
Q

How do disk stars orbit the center of the galaxy?

A

They all orbit in roughly the same plane and in the same direction

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15
Q

How do we know the total mass of the Milky Way Galaxy that is contained within the Sun’s orbital path?

A

by applying Newton’s version of Kepler’s third law (or the equivalent orbital velocity law) to the Sun’s orbit around the center of the Galaxy

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16
Q

Heavy elements constitute what percent of the mass of the interstellar medium?

A

2%

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17
Q

What do we mean by the star-gas-star cycle?

A

It is the continuous recycling of gas in the galactic disk between stars and the interstellar medium

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18
Q

What are cosmic rays?

A

subatomic particles that travel close to the speed of light

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19
Q

The primary way that we observe the atomic hydrogen that makes up most of the interstellar gas in the Milky Way is with _________.

A

radio telescopes observing at a wavelength of 21cm

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20
Q

Which of the following molecules is the most abundant in molecular clouds?

A

h2 (hydrogen)

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21
Q

What does interstellar dust mostly consist of?

A

microscopic particles of carbon and silicon

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22
Q

Which of the following models best explains why our galaxy has spiral arms?

A

The spiral arms are a wave of star formation caused by wave of density propagating outward through the disk of the galaxy.

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23
Q

What is a protogalactic cloud?

A

a cloud of hydrogen and helium that contracts to become a galaxy

24
Q

What is the age of most stars in the halo?

A

very old

25
Q

What is an ionization nebula?

A

A colorful cloud of gas that glows because it is heated by light from nearby stars

26
Q

What do halo stars do differently from disk stars?

A

they orbit the galactic center with many different inclinations, while disk stars all orbit in nearly the same plane

27
Q

Where do most stars form in the Milky Way?

A

in the spiral arms

28
Q

Based on observations, which of the following statements about stars in the Milky Way is generally true?

A

the older the star, the lower its abundance of heavy elements

29
Q

What kind of object do we think lies in the center of the milky way?

A

a 3 to 4 million solar mass black hole

30
Q

What is Hubble’s Law?

A

a relationship between the distance of a galaxy and the speed at which it is moving away from us

31
Q

What do we have to calibrate before using Hubble’s Law?

A

by measuring the distances to many distant galaxies with a standard candle technique

32
Q

What best describes the meaning of Hubble’s constant?

A

it describes the expansion rate of the universe, with high values meaning more rapid expansion

33
Q

When we observe a distant galaxy whose photons have traveled for 10 billion years before reaching Earth, we are seeing that galaxy as it was when the universe was

A

4 billion years old

34
Q

We can in principle measure the expansion rate by studying galaxies in many different directions in space and at different times of year. If we compare such observations, we would find that the expansion rate is __________.

A

the same no matter when or in which direction we measure it

35
Q

Why should galaxy collisions have been more common in the past than they are today?

A

galaxies were closer together in the past because the universe was smaller

36
Q

Dark matter is thought to exist because?

A

we can observe its gravitational influence on visible matter

37
Q

Dark energy has been hypothesized to exist in order to explain what?

A

observations suggesting that the expansion of the universe is accelerating

38
Q

The flat part of the milky ways rotation curve tells us that stars in the outskirts of the galaxy:

A

orbit the galactic center just as fast as stars closer to the center

39
Q

Strong evidence for the existence of dark matter comes from the observations of:

A

clusters of galaxies

40
Q

A photograph of a cluster of galaxies shows distorted images of galaxies that lie behind it at greater distances. This is an example of what astronomers call:

A

a gravitational lens

41
Q

Which region of the early universe was most likely to become a galaxy?

A

a region whose matter density was higher than average

42
Q

The major evidence for the idea that expansion of the universe is accelerating comes from the observations of:

A

white dwarf supernovae

43
Q

What happens when a proton collides with an antiproton?

A

they convert into 2 photons

44
Q

What is the charge of an antiproton?

A

negative

45
Q

Has the universe been cooling or heating up since the Big Bang?

A

cooling

46
Q

Hotter objects emit light with a:

A

shorter peak wavelength

47
Q

If the current density of normal matter in the universe were 10 times as great as it is now, we would expect to observe

A

less deuterium

48
Q

What does inflation help to explain?

A

the uniformity of the cosmic microwave background

49
Q

When did life on earth arise?

A

within a few hundred million years after birth

50
Q

The key requirement for life is what?

A

liquid water

51
Q

Which of the following is not considered crucial for life to exist on some world?

A

an atmosphere

52
Q

Which of the following best describes what we mean by a habitable world?

A

a planet or moon that could support life, if any life happened to be on it

53
Q

What is the Sun’s habitable zone?

A

it extends from slightly beyond Venus’s orbit to near the orbit of Mars

54
Q

The “rare Earth hypothesis” holds that Earth-like planets will prove to be quite rare. Which of the following statements best sums up the current status of the debate over this hypothesis?

A

We do not have enough data to settle the debate, because counterarguments can be made for each argument suggesting Earth-like planets may be rare.

55
Q

At present, what is the primary way that the search for extraterrestrial intelligence (SETI) is carried out?

A

by using radio telescopes to search for signals

56
Q

In the Drake equation (Number of Civilizations = N HP × f life × f civ × f now), what do we mean by f now?

A

the fraction of planets with civilizations at the present time

57
Q

Einstein’s theory of relativity tells us that travelers who make a high-speed trip to a distant star and back will _________.

A

age less than people who stay behind on Earth

Visions of the Universe (4 decks)

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