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Flashcards in Mastering Astronomy Timed quiz 4 Deck (54):
1

Approximately, what basic composition are all stars born with?

90 percent hydrogen, 10 percent helium, no more than 1 percent heavier elements
one-quarter hydrogen, three-quarters helium, no more than 2 percent heavier elements
three-quarters hydrogen, one-quarter helium, no more than 2 percent heavier elements
98 percent hydrogen, 2 percent helium
half hydrogen, half helium, no more than 2 percent heavier elements

three-quarters hydrogen, one-quarter helium, no more than 2 percent heavier elements

2

Since all stars begin their lives with the same basic composition, what characteristic most determines how they will differ?

mass they are formed with
time they are formed
location where they are formed
color they are formed with
luminosity they are formed with

mass they were formed with

3

What are the standard units for luminosity?

joules
Newtons
kilograms
watts per second
watts

watts

4

What are the standard units for apparent brightness?

Newtons
watts
watts per square meter
joules
watts per second

watts per square meter

5

Which of the following correctly states the luminosity-distance formula?

distance =
apparent brightness = luminosity × 4π × (distance)2
luminosity =
apparent brightness =

apparent brightness = luminosity / 4pie x (distance)^2

6

Why do astronomers often measure the visible-light apparent brightness instead of the total apparent brightness of a star?

Astronomers are lazy.
All stars put out most of their light in the visible range of the spectrum.
They are identical for most stars.
Most stars do not put out light in other ranges of the spectrum.
In order to measure the total apparent brightness of a star, you must measure its brightness in all wavelengths, and this is difficult to do. The only wavelengths you can measure from the surface of Earth are visible and radio wavelengths.

In order to measure the total apparent brightness of a star, you must measure its brightness in all wavelengths, and this is difficult to do. The only wavelengths you can measure from the surface of Earth are visible and radio wavelengths.

7

The most distant stars we can measure stellar parallax for are approximately

5,000 parsecs away.
halfway across the Milky Way Galaxy.
50 parsecs away.
500 parsecs away.
in the Andromeda Galaxy.

50 parsecs away.

8

Which of the following statements about apparent and absolute magnitudes is true?

A star with apparent magnitude 1 is brighter than one with apparent magnitude 2.
A star's absolute magnitude is the apparent magnitude it would have if it were at a distance of 10 parsecs from Earth.
The absolute magnitude of a star is another measure of its luminosity.
The magnitude system that we use now is based on a system used by the ancient Greeks over 2,000 years ago that classified stars by how bright they appeared.
All of the above are true.

all of the above are true

9

The spectral sequence sorts stars according to

surface temperature.
mass.
radius.
core temperature.
luminosity.

surface temperature

10

The spectral sequence in order of decreasing temperature is

OBAFGKM.
BAGFKMO.
OBAGFKM.
ABFGKMO.
OFBAGKM.

OBAFGKM

11

Why is the spectral sequence of stars not alphabetical?

Because there is still uncertainty over what generates the energy in stellar cores.
The original alphabetical labeling did not correspond to surface temperature and thus had to be reordered.
Because it refers to stellar masses and these were difficult to measure accurately.
The letters refer to the initials of the original discovers.
They were chosen to fit a mnemonic.

The original alphabetical labeling did not correspond to surface temperature and thus had to be reordered.

12

Which of the following statements about spectral types of stars is true?

The spectral type of a star can be used to determine its color.
A star with spectral type F2 is hotter than a star with spectral type F3.
A star with spectral type A is cooler than a star with spectral type B.
The spectral type of a star can be used to determine its surface temperature.
All of the above are true.

all of the above are true

13

Which of the following persons reorganized the spectral classification scheme into the one we use today and personally classified over 400,000 stars?

Annie Jump Cannon
Williamina Fleming
Henry Draper
Cecilia Payne-Gaposchkin
Edward Pickering

Annie Jump Cannon

14

On a Hertzsprung-Russell diagram, where would we find stars that are cool and luminous?

upper right
lower right
upper left
lower left

Upper right

15

On a Hertzsprung-Russell diagram, where would we find stars that have the largest radii?

upper right
lower right
upper left
lower left

Upper right

16

On a Hertzsprung-Russell diagram, where on the main sequence would we find stars that have the greatest mass?

upper right
lower right
upper left
lower left

Upper left

17

On a Hertzsprung-Russell diagram, where would we find red giant stars?

upper right
lower right
upper left
lower left

Upper right

18

You observe a star in the disk of the Milky Way, and you want to plot the star on an H-R diagram. You will need to determine all of the following, except the

spectral type of the star.
apparent brightness of the star in our sky.
distance to the star.
rotation rate of the star.

Rotation rate of the star

19

A star of spectral type G lives approximately how long on the main sequence?

100 million years
10,000 years
10 billion years
1 million years
1,000 years

10 billion years

20

Which of the following luminosity classes refers to stars on the main sequence?

II
V
III
I
IV

V

21

Cluster ages can be determined from

main sequence turnoff.
main sequence fitting.
visual binaries.
pulsating variable stars.
spectroscopic binaries.

main sequence turnoff.

22

In order to understand star clusters, we need to be able to estimate their ages. What technique do scientists use for this?

radioisotope dating
finding the main-sequence turnoff point of the stars
measuring its parallax
calculating orbital parameters using Kepler's Laws
counting the planets that have formed around the largest stars

finding the main-sequence turnoff point of the stars

23

What do astronomers mean when they say that we are all "star stuff"?

that life would be impossible without energy from the Sun
that the carbon, oxygen, and many elements essential to life were created by nucleosynthesis in stellar cores
that Earth formed at the same time as the Sun
that the Universe contains billions of stars
that the Sun formed from the interstellar medium: the "stuff" between the stars

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

24

All of the following are involved in carrying energy outward from a star's core except

radiative diffusion.
convection.
neutrinos.
conduction.

conduction.

25

Which stars have convective cores?

high-mass stars
intermediate-mass stars
low-mass stars
all of the above
none of the above

High mass stars

26

What is happening inside a star while it expands into a subgiant?

It is fusing hydrogen into helium in a shell outside the core.
It is fusing helium into carbon in a shell outside the core.
It is not fusing any element; it is contracting and heating up.
It is fusing helium into carbon in the core.
It is fusing hydrogen into helium in the core.

It is fusing hydrogen into helium in a shell outside the core.

27

Compared to the star it evolved from, a red giant is

cooler and brighter.
the same temperature and brightness.
hotter and dimmer.
hotter and brighter.
cooler and dimmer.

cooler and brighter.

28

At approximately what temperature can helium fusion occur?

a few million K
100 million K
100 billion K
100,000 K
1 million K

100 million K

29

The helium fusion process results in the production of

carbon.
oxygen.
nitrogen.
iron.
hydrogen.

carbon.

30

Which of the following sequences correctly describes the stages of life for a low-mass star?

white dwarf, main-sequence, red giant, protostar
protostar, main-sequence, white dwarf, red giant
protostar, red giant, main-sequence, white dwarf
protostar, main-sequence, red giant, white dwarf
red giant, protostar, main-sequence, white dwarf

protostar, main-sequence, red giant, white dwarf

31

During which stage is the star's energy supplied by gravitational contraction?

ii
v
vi
iii
viii

ii

32

During which stage does the star have an inert (nonburning) carbon core?

vi
ii
iii
iv
viii

viii

33

Which stage lasts the longest?

vi
iv
viii
i
iii

iii

34

In the end, the remaining core of this star will be left behind as

a black hole.
a neutron star.
a white dwarf made primarily of carbon and oxygen.
a supernova.
a white dwarf made primarily of silicon and iron.

a white dwarf made primarily of carbon and oxygen.

35

Based on its main-sequence turnoff point, the age of this cluster is

more than 15 billion years.
about 1 billion years.
less than 1 billion years.
about 2 billion years.
about 10 billion years.

about 10 billion years.

36

You discover a binary star system in which one member is a 15MSun main-sequence star and the other star is a 10MSun giant. Why should you be surprised, at least at first?

It doesn't make sense to find a giant in a binary star system.
The two stars in a binary system should both be at the same point in stellar evolution; that is, they should either both be main-sequence stars or both be giants.
The odds of ever finding two such massive stars in the same binary system are so small as to make it inconceivable that such a system could be discovered.
The two stars should be the same age, so the more massive one should have become a giant first.
A star with a mass of 15MSun is too big to be a main-sequence star.

The two stars should be the same age, so the more massive one should have become a giant first

37

Degeneracy pressure is the source of the pressure that stops the crush of gravity in all the following except

a very massive main-sequence star.
a brown dwarf.
the central core of the Sun after hydrogen fusion ceases but before helium fusion begins.
a white dwarf.
a neutron star.

a very massive main-sequence star.

38

Why is there an upper limit to the mass of a white dwarf?

The upper limit to the masses of white dwarfs was determined through observations of white dwarfs, but no one knows why the limit exists.
White dwarfs come only from stars smaller than 1.4 solar masses.
Above this mass, the electrons would be pushed together so closely they would turn into neutrons and the star would become a neutron star.
The more massive the white dwarf, the higher its temperature and hence the greater its degeneracy pressure. At about 1.4 solar masses, the temperature becomes so high that all matter effectively melts, even individual subatomic particles.
The more massive the white dwarf, the greater the degeneracy pressure and the faster the speeds of its electrons. Near 1.4 solar masses, the speeds of the electrons approach the speed of light, so more mass cannot be added without breaking the degeneracy pressure.

The more massive the white dwarf, the greater the degeneracy pressure and the faster the speeds of its electrons. Near 1.4 solar masses, the speeds of the electrons approach the speed of light, so more mass cannot be added without breaking the degeneracy pressure.

39

Suppose a white dwarf is gaining mass because of accretion in a binary system. What happens if the mass someday reaches the 1.4-solar-mass limit?

The white dwarf immediately collapses into a black hole, disappearing from view.
The white dwarf, which is made mostly of carbon, suddenly becomes much hotter in temperature and therefore is able to begin fusing the carbon. This turns the white dwarf back into a star supported against gravity by ordinary pressure.
The white dwarf undergoes a catastrophic collapse, leading to a type of supernova that is somewhat different from that which occurs in a massive star but is comparable in energy.
A white dwarf can never gain enough mass to reach the limit because a strong stellar wind prevents the material from reaching it in the first place.

The white dwarf undergoes a catastrophic collapse, leading to a type of supernova that is somewhat different from that which occurs in a massive star but is comparable in energy.

40

Which of the following statements about novae is not true?

A star system that undergoes a nova may have another nova sometime in the future.
The word nova means "new star" and originally referred to stars that suddenly appeared in the sky, then disappeared again after a few weeks or months.
A nova involves fusion taking place on the surface of a white dwarf.
When a star system undergoes a nova, it brightens considerably, but not as much as a star system undergoing a supernova.
Our Sun will probably undergo at least one nova when it becomes a white dwarf about 5 billion years from now.

Our Sun will probably undergo at least one nova when it becomes a white dwarf about 5 billion years from now.

41

Observationally, how can we tell the difference between a white-dwarf supernova and a massive-star supernova?

The spectrum of a massive-star supernova shows prominent hydrogen lines, while the spectrum of a white-dwarf supernova does not.
We cannot yet tell the difference between a massive-star supernova and a white-dwarf supernova.
The light of a white-dwarf supernova fades steadily, while the light of a massive-star supernova brightens for many weeks.
A massive-star supernova happens only once, while a white-dwarf supernova can repeat periodically.
A massive-star supernova is brighter than a white-dwarf supernova.

The spectrum of a massive-star supernova shows prominent hydrogen lines, while the spectrum of a white-dwarf supernova does not.

42

Which of the following is closest in size (radius) to a neutron star?

the Sun
a basketball
a football stadium
a city
Earth

a city

43

Which of the following best describes what would happen if a 1.5-solar-mass neutron star, with a diameter of a few kilometers, were suddenly (for unexplained reasons) to appear in your hometown?

The entire mass of Earth would end up as a thin layer, about 1 cm thick, over the surface of the neutron star.
It would crash into Earth, throwing vast amounts of dust into the atmosphere which in turn would cool Earth. Such a scenario is probably what caused the extinction of the dinosaurs.
It would crash through Earth, creating a large crater, and exit Earth on the other side.
The combined mass of Earth and the neutron star would cause the neutron star to collapse into a black hole.
It would rapidly sink to the center of Earth.

The entire mass of Earth would end up as a thin layer, about 1 cm thick, over the surface of the neutron star.

44

From an observational standpoint, what is a pulsar?

a star that slowly changes its brightness, getting dimmer and then brighter with a period of anywhere from a few hours to a few weeks
an object that emits random "pulses" of light that sometimes occur only a fraction of a second apart and other times stop for several days at a time
a star that rapidly changes size as it moves off the main sequence
an object that emits flashes of light several times per second or more, with near perfect regularity
a star that changes color rapidly, from blue to red and back again

an object that emits flashes of light several times per second or more, with near perfect regularity

45

What causes the radio pulses of a pulsar?

The star's orbiting companion periodically eclipses the radio waves emitted by the main pulsar.
A black hole near the star absorbs energy and re-emits it as radio waves.
The star vibrates.
As the star spins, beams of radio radiation sweep through space. If one of the beams crosses Earth, we observe a pulse.
The star undergoes periodic explosions of nuclear fusion that generate radio emission.

As the star spins, beams of radio radiation sweep through space. If one of the beams crosses Earth, we observe a pulse.

46

How does a black hole form from a massive star?

If enough mass is accreted by a white-dwarf star so that it exceeds the 1.4-solar-mass limit, it will undergo a supernova explosion and leave behind a black-hole remnant.
If enough mass is accreted by a neutron star, it will undergo a supernova explosion and leave behind a black-hole remnant.
During a supernova, if a star is massive enough for its gravity to overcome neutron degeneracy of the core, the core will be compressed until it becomes a black hole.
A black hole forms when two massive main-sequence stars collide.
Any star that is more massive than 8 solar masses will undergo a supernova explosion and leave behind a black-hole remnant.

During a supernova, if a star is massive enough for its gravity to overcome neutron degeneracy of the core, the core will be compressed until it becomes a black hole.

47

What do we mean by the singularity of a black hole?

It is the edge of the black hole, where one could leave the observable universe.
An object can become a black hole only once, and a black hole cannot evolve into anything else.
It is the center of the black hole, a place of infinite density where the known laws of physics cannot describe the conditions.
It is the "point of no return" of the black hole; anything closer than this point will not be able to escape the gravitational force of the black hole.
There are no binary black holes—each one is isolated.

It is the center of the black hole, a place of infinite density where the known laws of physics cannot describe the conditions.

48

Why do astronomers consider gamma-ray bursts to be one of the greatest mysteries in astronomy?

because we know they come from pulsating variable stars but don't know how they are created
because they are so rare
because current evidence suggests that they come from our own Milky Way, but we have no idea where in the Milky Way they occur
because the current evidence suggests that they are the most powerful bursts of energy that ever occur anywhere in the universe, but we don't know how they are produced
because current evidence suggests that they come from massive black holes in the centers of distant galaxies, adding to the mystery of black holes themselves

because the current evidence suggests that they are the most powerful bursts of energy that ever occur anywhere in the universe, but we don't know how they are produced

49

An advanced civilization lives on a planet orbiting a close binary star system that consists of a 15MSun red giant and a 10MSun black hole. Assume that the two stars are quite close together, so that an accretion disk surrounds the black hole. The planet on which the civilization lives orbits the binary star at a distance of 10 AU.


One foolhardy day, a daring major (let's call him Tom) in the space force decides to become the first of his race to cross the event horizon of the black hole. To add to the drama, he decides to go in wearing only a thin space suit, which offers no shielding against radiation, no cushioning against any forces, and so on. Which of the following is most likely to kill him first (or at least cause significant damage)? (Hint: The key word here is first. Be sure to consider the distances from the black hole at which each of the noted effects is likely to become damaging.)

the sucking force from the black hole, which will cause his head to explode
the X rays from the accretion disk
the crush of gravity at the singularity embedded within the black hole
the tidal forces due to the black hole
the strong acceleration as he descends towards the black hole

the X rays from the accretion disk

50

If you were to come back to our Solar System in 6 billion years, what might you expect to find?

Everything will be pretty much the same as it is now.
a rapidly spinning pulsar
a black hole
a white dwarf
a red giant star

a white dwarf

51

Keplers 3 laws

Law of ellipses
Law of equal areas
Law of harmonies t^2= R^3
Period ^2 = distance ^3

52

Newton's first law

Law of inertia

Object at rest remains at rest...

53

Newtons 2nd law

Force = mass times acceleration

54

Newtons 3rd law

For every action there is an opposite and equal reaction