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Flashcards in Chapter 12 Deck (35):
1

Which two processes can generate energy to help a star maintain its internal thermal pressure?

nuclear fusion and gravitational contraction

2

Our Sun is considered to be a ________.

low mass star

3

Which process is required to allow a gravitationally-collapsing gas cloud to continue to collapse?

The cloud must radiate much of its thermal energy.

4

Angular momentum plays an important role in star formation. Which of the following characteristics of a protostellar system is probably not strongly affected by the star's angular momentum?
the onset of core hydrogen fusion
the formation of a protostellar disk
the existence of protostellar jets
the strength of protostellar winds

the onset of core hydrogen fusion

5

Generally speaking, how does the surface temperature and luminosity of a protostar compare to the surface temperature and luminosity of the main-sequence star it becomes?

A main-sequence star is hotter and dimmer than it was as a protostar.

6

Consider a large molecular cloud that will give birth to a cluster of stars. Which of the following would you expect to be true?
All the stars in the cluster will be of about the same mass.
A few massive stars will form, live, and die before the majority of the star's clusters even complete their protostar stage.
All the stars in the cluster will become main-sequence stars at about the same time.
All the stars in the cluster will have approximately the same luminosity and surface temperature.

A few massive stars will form, live, and die before the majority of the star's clusters even complete their protostar stage.

7

We do not know for certain whether the general trends we observe in stellar birth masses also apply to brown dwarfs. But if they do, then which of the following would be true?

Brown dwarfs would outnumber all ordinary stars.

8

Where would a brown dwarf be located on an H-R diagram?

below and to the right of the lowest part of the main sequence

9

Which of the following types of data provide evidence that helps us understand the life tracks of low-mass stars?
observing a low-mass star over many years
H-R diagrams of open clusters
spacecraft observations of the Sun
H-R diagrams of globular clusters

H-R diagrams of globular clusters

10

Why is a 1 solar-mass red giant more luminous than a 1 solar-mass main sequence star?

Fusion reactions are producing energy at a greater rate in the red giant.

11

Carbon fusion occur in high-mass stars but not in low-mass stars because ________.

the cores of low-mass stars never get hot enough for carbon fusion

12

Which of the following statements about various stages of core nuclear burning (hydrogen, helium, carbon, and so on) in a high-mass star is not true?
Each successive stage lasts for approximately the same amount of time.
As each stage ends, the reactions that occurred in previous stages continue in shells around the core.
As each stage ends, the core shrinks and heats further.
Each successive stage creates an element with a higher atomic number and atomic mass number.

Each successive stage lasts for approximately the same amount of time.

13

Which event marks the beginning of a supernova?

The sudden collapse of an iron core into a compact ball of neutrons

14

Suppose that the star Betelgeuse (the upper left shoulder of Orion) were to supernova tomorrow (as seen here on Earth). What would it look like to the naked eye?

Betelgeuse would remain a dot of light, but would suddenly become so bright that, for a few weeks, we'd be able to see this dot in the daytime.

15

Observations show that elements with atomic mass numbers divisible by 4 (such as oxygen — 16, neon — 20, and magnesium — 24) tend to be more abundant in the universe than elements with atomic mass numbers in between. Why do we think this is the case?

At the end of a high-mass star's life, it produces new elements through a series of helium capture reactions.

16

You discover a binary star system in which one star is a 15 MSun main-sequence star and the other is a
10 MSun giant. How do we think that a star system such as this might have come to exist?

The giant must once have been the more massive star, but is now less massive because it transferred some of its mass to its companion.

17

What did Carl Sagan mean when he said that we are all "star stuff"?

that the carbon, oxygen, and other elements essential to life were created by nucleosynthesis in stellar cores

18

Which two energy sources can help a star maintain its internal thermal pressure?

nuclear fusion and gravitational contraction

19

No stars are expected with masses greater than 150 times our Sun because

they would generate so much power that they would blow themselves apart.

20

Which of the following statements about degeneracy pressure is not true?
Degeneracy pressure is a consequence of the laws of quantum mechanics.
Degeneracy pressure keeps any protostar less than 0.08 solar mass from becoming a true, hydrogen-fusing star.
Degeneracy pressure varies with the temperature of the star.
Degeneracy pressure can halt gravitational contraction of a star even when no fusion is occurring in the core.

Degeneracy pressure varies with the temperature of the star.

21

What is the fate of an isolated brown dwarf?

it will remain a brown dwarf forever

22

What happens when a star like the sun exhausts its core hydrogen supply?

Its core contracts, but its outer layers expand and the star becomes bigger and brighter.

23

At approximately what temperature can helium fusion occur?

100 million K

24

After a supernova event occurring in a high-mass star, what is left behind?

either a neutron star or a black hole

25

Why is Supernova 1987A particularly important to astronomers?


It was the nearest supernova detected in nearly 400 years.

26

What kind of gas cloud is most likely to give birth to stars?

a cold, dense gas cloud

27

Which of the following phenomena is not commonly associated with the star formation process?
the formation of a spinning disk of material around a protostar
powerful "jets" shooting out along the rotation axis of a protostar
intense ultraviolet radiation coming from a protostar
strong winds of particles blowing out into space from a protostar

intense ultraviolet radiation coming from a protostar

28

When does a protostar become a main-sequence star?

when the rate of hydrogen fusion becomes high enough to balance the rate at which the star radiates energy into space

29

Which star spends the longest time in the protostellar phase of life?

a 1 solar mass star

30

The main source of energy for a star as it grows in size to become a red giant is ________.

hydrogen fusion in a shell surrounding the central core

31

What is a helium flash?

The sudden onset of helium fusion in the core of a low-mass star

32

What is the CNO cycle?

a set of steps by which four hydrogen nuclei fuse into one helium nucleus

33

Why is iron significant to understanding how a supernova occurs?

Iron cannot release energy either by fission or fusion

34

After a supernova explosion, the remains of the stellar core ________.

may be either a neutron star or a black hole

35

Algol consists of a 3.7 MSun main-sequence star and a 0.8 MSun subgiant. Why does this seem surprising, at least at first?

The two stars should be the same age, so we'd expect the subgiant to be more massive than the main-sequence star.