question

Dust reddens starlight because

answer

it scatters optical and higher-frequency light

question

Dust appears dark in ___________ wavelengths and bright in ___________ wavelengths.

answer

optical; infrared

question

Sitting in a 100° F hot tub feels much hotter than standing outside on a 100° F day. This analogy illustrates why

answer

an astronaut would feel cold in 10⁶ K intercloud gas

question

Which of the following is responsible for heating the bulk of the very hot intercloud gas?

answer

Supernovae

question

Warm ionized gas will appear ___________ when imaged in the optical portion of the spectrum.

answer

red

question

H II regions are powered by

answer

young O and B stars

question

21-cm radiation is important because

answer

it allows us to study neutral hydrogen in the interstellar medium

question

In the interstellar medium, molecules survive only in regions with

answer

all of the above

question

Molecular clouds are best observed at ___________ wavelengths.

answer

radio

question

Interstellar clouds are

answer

regions where hydrogen tends to be denser than the surrounding gas

question

"Weather" in the interstellar medium is produced

answer

by supernovae and strong winds from luminous stars

question

Of the following forces at work in molecular clouds, which inevitably dominates the clouds' evolution?

answer

Gravity

question

A young protostar is ___________ than the sun even though its surface temperature is ___________.

answer

more luminous; cooler

question

What happens as a protostar contracts?

answer

All of the above are true

question

The entire process of star formation is really just an evolving balance between

answer

pressure and gravity

question

A cloud fragment too small to form a star becomes

answer

a brown dwarf

question

The source of energy for a contracting protostar comes from

answer

gravitational potential energy

question

A Hayashi track on an H-R diagram is a path of approximately constant

answer

temperature

question

The most common types of stars in our galaxy are

answer

low-mass stars

question

Which of the following stars spend the longest time on their Hayashi tracks?

answer

0.1 M₀ stars

question

A star's evolutionary "track" in the H-R diagram traces out

answer

how the star's luminosity, temperature, and size change with time

question

A main sequence star is distinguished by

answer

hydrogen burning in its core

question

The evolutionary cutoff between low- and high-mass stars occurs around

answer

3 M₀

question

What factor is most important in determining a star's position on the main sequence and subsequent evolution?

answer

Mass

question

The main sequence lifetime of a star is given by the equation

answer

t = M/L

question

As a main sequence star burns its core supply of hydrogen, what happens?

answer

Helium builds up as ash in the core

question

The luminosity of a star depends on

answer

how efficient its fuel is and how fast it burns

question

Hydrogen shell burning proceeds increasingly faster due to

answer

heat released from the core's contraction

question

The sun will likely stop being a main sequence star in

answer

5 billion years

question

When a G2 star leaves the main sequence,

answer

its luminosity increases and its surface temperature decreases

question

Degenerate refers to a state of

answer

high density

question

Just as a low-mass main sequence star runs out of fuel in its core, it actually becomes more luminous. How is this possible?

answer

The outer layers expand due to the high rate of fusion in a shell around the dead core

question

When a star depletes its core supply of hydrogen, ___________ dominates in the core and ____________ dominates in the atmosphere.

answer

gravity; pressure

question

A low-mass main sequence star's climb up the red giant branch is halted by

answer

the beginning of helium fusion in the core

question

When helium fusion begins in the core of the star, the situation quickly gets out of control because electron degeneracy pressure does not respond to changes in

answer

temperature

question

A star's surface temperature during the horizontal branch phase is determined primarily by its

answer

chemical composition

question

Asymptotic giant branch (AGB) stars lose their atmosphere because

answer

they have a low surface gravity

question

What is a planetary nebula?

answer

The ejected envelope of a giant star surrounding a stellar core remnant

question

In a white dwarf, what is the source of pressure that halts its contraction as it cools?

answer

Electrons packed so closely that they become incompressible

question

The gas in a planetary nebula comes from

answer

hydrogen and elements processed in the core of the post-asymptotic giant branch star

question

One star in a binary will almost always become a red giant before the other because

answer

small differences in main sequence masses yield large differences in main sequence ages

question

A nova is the result of which explosive situtation?

answer

Mass transfer onto a white dwarf

question

A Type I supernova occurs when a white dwarf exceeds a mass of ____________.

answer

1.4 M₀

question

A Cepheid star varies in luminosity because

answer

only the outer envelope of the star pulsates

question

Hawking radiation exists from black holes because

answer

space itself has physical properties

question

At about what mass do we distinguish between high-mass and low-mass stars?

answer

8 M₀

question

The more efficient CNO cycle of hydrogen fusion can take place in high-mass stars because of the greater ___________ in their cores.

answer

temperatures

question

What prevents the buildup of a core of helium ash in a high-mass main sequence star?

answer

Mixing by convection

question

As a high-mass main sequence star evolves off the main sequence, it follows a ___________ the HR diagram.

answer

roughly horizontal path

question

When pulsating variable stars are at their brightest, they are also

answer

largest and bluest

question

The main difference between Cepheid variable stars and RR Lyrae stars is

answer

their masses

question

If you measure the pulsation period of a Cepheid variable star, you can also determine its

answer

distance

question

An iron core cannot support a star because

answer

iron cannot fuse with other nuclei to produce energy

question

Why does the luminosity of a high-mass star remain nearly constant as the star burns heavy elements in its core, even though it is producing millions of times more energy per second than it did on the main sequence?

answer

The energy is carried off in the form of neutrinos

question

The collapse of the core of a high-mass star at the end of its life takes about

answer

one second

question

Essentially all the heaviest elements in the galaxy are formed during

answer

a supernova explosion

question

A neutron star contains the mass of up to three Suns in a sphere with a diameter approximately the size of

answer

Manhattan

question

Which of the following does not describe a neutron star?

answer

All of these describe a neutron star

question

What characteristic of a star cluster is used to determine its age?

answer

The main sequence turnoff point

question

X-ray binaries result from a process similar to that in a

answer

a nova

question

What would happen if mass were continually added to a 2.0 solar mass neutron star?

answer

The star would eventually become a black hole

question

Light is increasingly redshifted near a black hole because

answer

time is moving increasing ly slower in the observer's frame of reference

question

The event horizon of a black hole is defined as

answer

the radius at which the escape speed equals the speed of light

question

If the Sun were to be replaced by a one solar mass black hole, the gravitational pull of the black hole "sun" on Earth would be

answer

the same

question

An indestructible robot would feel ____________ as it crossed the event horizon of a black hole

answer

nothing

question

Black holes are best studied in the ____________ band of radiation.

answer

X-ray

question

What do astronomers mean when they say that the universe is homogeneous?

answer

Stars and galaxies are generally distributed similarly throughout the universe

question

The spectra of most galaxies tell us that

answer

most galaxies appear to be moving away from us

question

According to Hubble's Law, as the distance of a galaxy ____________; its _____________ increases.

answer

increases; recessional velocity

question

Hubble's constant H₀ represents

answer

the rate of expansion of the universe

question

Astronomers use galactic redshift as a measure of

answer

distance

question

If suddenly we find that the distance between Earth and the Sun is not 10 percent larger than we thought it was before, what will change?

answer

All of the above

question

If we lived on a galaxy one billion light-years from our own, what would we see?

answer

Much the same universe we see today

question

If you lived today on the farthest quasar we can see and looked around, what would you see?

answer

A universe much as we see it today

question

Galaxies move away from us in all directions because

answer

space is expanding

question

Where in the universe did the Big Bang take place?

answer

Everywhere in the universe

question

Assuming a Hubble time of 13.6 billion years and a constant rate of expansion, what was the scale factor (R₀) of the universe 10.2 billion years ago (compared to today)?

answer

0.25

question

At a redshift of z = 1,000, the universe was

answer

1000 times smaller than it is today

question

The temperature of the cosmic background radiation 2.73 K corresponds to a peak wavelength of around

answer

1,000 um

question

If, at the time of recombination, the wavelength of the background radiation peaked at 1 um, how old was the universe, compared to today?

answer

1/1,000th as old

question

Which of the following elements was not created as a result of Big Bang nucleosynthesis?

answer

Carbon

question

Why does the overall mass of the universe decide its ultimate fate?

answer

The greater the mass of the universe, the more gravitationally bound the universe will be.

question

If the fate of the universe were determined solely by the total mass of the universe (luminous and dark), astronomers would predict that we live in a universe that will

answer

stop expanding and eventually copllapse

question

How does the addition of a nonzero cosmological constant affect the expansion of the universe?

answer

It is possible for the density of the universe to be above the critical mass density and still expand forever

question

The fact that we live in an accelerating universe indicates that the age of the universe is ____________ the Hubble time.

answer

older than

question

The inverse of the value of H₀ is

answer

a time

question

In a spherical universe, the sum of the angles in a triangle sum to

answer

more than 180°

question

Why is the fact that the cosmic background radiation (CBR) is near smooth considered a problem?

answer

A universe as smooth as predicted by the CBR should never have occurred because quantum mechanics states that the universe had to have started with fluctuations too great to have smoothed out

question

Protostars are difficult to observe because

answer

a. the protostar stage is very short. b. they are surrounded by cocoons of gas and dust. c. they radiate mainly in the infrared.

question

Interstellar gas clouds may collapse to form stars if they

answer

encounter a shock wave.

question

____ are small luminous nebulae excited by nearby young stars.

answer

Herbig-Haro objects

question

Opacity is

answer

a measure of the resistance to the flow of radiation (photons) through a gas.

question

The visual pink glow of the Great Nebula in Orion

answer

is an emission nebula of thin gas.

question

The ____ is the nuclear fusion of three helium nuclei to form a carbon nucleus.

answer

triple-alpha process

question

Emission nebulae are also called ____ because they are composed of ionized hydrogen.

answer

HII regions

question

____ are star-like objects that contain less than 0.08 solar masses and will never raise their core temperatures high enough that the proton-proton chain can begin. Other minor fusion reactions do occur in these objects. They fall in a gap between the low-mass M dwarf stars and the massive planets in which nuclear fusion never occurs.

answer

Brown dwarfs

question

The average star spends ____ of its lifetime on the main sequence.

answer

90%

question

The lower edge of the Main Sequence band is known as ____ and represents the location in the H-R diagram at which stars begin their lives as main sequence stars.

answer

the zero-age main sequence

question

____ is the thermonuclear fusion of hydrogen to form helium operating in the cores of massive stars on the main sequence.

answer

The CNO cycle

question

The diagram below is an H-R diagram. The line indicates the location of the main sequence. Which of the five labeled locations on the HR diagram indicates a luminosity and temperature similar to that of a T Tauri star?

answer

4

question

In the proton-proton chain

answer

energy is produced in the form of gamma rays and the velocity of the created nuclei.

question

The carbon-nitrogen-oxygen cycle

answer

combines four hydrogen nuclei to form one helium nucleus, which produces energy.

question

What causes the outward gas pressure that balances the inward pull of gravity in a main sequence star?

answer

c. the high temperature of the gas d. the high density of the gas

question

The free-fall contraction of a molecular cloud

answer

can be initiated by shock waves from supernovae.

question

Convection is important in stars because it

answer

b. mixes the gases of the star. c. transports energy outward in the star.

question

____ occurs when most of the material collapsing to form a protostar has fallen into a disk around the star, and a strong wind from the warm protostar ejects material from its poles.

answer

A bipolar outflow

question

Which of the following is NOT evidence of the existence of an interstellar medium?

answer

molecular absorption lines in the spectra of cool stars `

question

Molecular clouds can be observed

answer

using radio telescopes to observe the CO emission from the clouds.

question

The H-R diagram main sequence of stars has a limit at the lower mass, or energy output end, because

answer

there is a minimum temperature for hydrogen nuclear fusion (the definition of a star).

question

There is a main sequence mass-luminosity relation because

answer

more massive stars support their larger weight by making more energy.

question

Due to the dust in the interstellar medium, a distant star will appear to an observer on Earth to be

answer

fainter and cooler than it really is.

question

The lowest mass object that can initiate thermonuclear fusion of hydrogen has a mass of about

answer

0.08 solar masses.

question

Stars with masses less than ____ produce most of their energy via the proton-proton chain.

answer

1.1 solar masses

question

The creation of ____ require(s) that a young hot star (T 25,000 K) be relatively nearby.

answer

emission nebulae

question

The extinction of starlight due to the interstellar medium

answer

I. is the greatest in the ultraviolet. IV. is caused by dust particles.

question

____ are small dark nebulae about 1 light-year in diameter that contain 10 to 1,000 solar masses.

answer

Bok globules

question

Absorption lines due to the interstellar medium indicate that some components of the interstellar medium are cold and of a very low density because

answer

the lines are extremely narrow.

question

Stars are born in

answer

dense molecular clouds.

question

Absorption lines due to interstellar gas

answer

are more narrow than the lines from stars because the gas has a lower pressure than stars.

question

What is the lifetime of a 10 solar mass star on the main sequence?

answer

3.2×107 years

question

What is the lifetime on the main sequence of a 2 solar mass star compared to the approximately 10 billion year life of our Sun? Pick the best answer.

answer

1.8×10^9 years

question

If the dust around a protostar radiates most strongly at 30 microns or 30,000 nm, what is the approximate temperature of that dust? Hint: T in K =3,000,000/wavelength in nm.

answer

100 K

question

A jet has an angular length of 10 seconds of arc and flows from a star at a distance of 2,000 pc. How far does this jet extend away from the star?

answer

20,000 AU

question

The H-R diagram of a young star cluster shows

answer

that low mass stars have not yet reached the main sequence yet.

question

As a star begins to form, the initial energy source is from

answer

gravitational potential energy.

question

While on the main sequence a star's primary energy source comes from

answer

nuclear fusion.

question

What must occur for an object to be considered a main sequence star?

answer

a. Hydrostatic equilibrium b. Nuclear fusion reaction in the core

question

What force(s) are responsible for the collapse of an interstellar cloud?

answer

gravity

question

Star clusters are important to the study the stellar evolution because stars in a given cluster have the same

answer

age.

question

Why do higher mass stars live shorter lives on the main sequence than lower mass stars?

answer

Higher mass stars burn through their nuclear fuel faster.

question

Why do nuclear fusion reactions only take place in the interior of a star?

answer

b. The temperature is the hottest in the center. c. The density of material is very high in the center.

question

What characteristic of a star primarily determines its location on the main sequence?

answer

mass

question

Parallax would be easier to measure if

answer

Earth's orbit was larger.

question

Absolute visual magnitude is

answer

the apparent magnitude of a star observed from a distance of 10 pc.

question

A star's luminosity depends only on the star's

answer

temperature and diameter.

question

In an H-R Diagram, stars with the smallest radius are found in the ____ of the diagram.

answer

lower left corner

question

In the H-R diagram, 90 percent of all stars are

answer

on the main sequence.

question

We know that giant stars are larger in diameter than the sun because

answer

they are more luminous but have about the same temperature.

question

Red giant stars are

answer

I. more luminous than the sun. II. larger in diameter than the sun. III. cooler than B stars. IV. located above the main sequence stars in the H-R diagram.

question

Compared with the spectral lines in the solar spectrum, lines in a supergiant star's spectrum are

answer

more narrow.

question

The most common stars are

answer

lower (less luminous) main sequence stars.

question

The ____ of a star is a measure of the total energy radiated by the star in one second.

answer

luminosity

question

To determine the orbital period of a visual binary, we must measure

answer

position on the sky.

question

In a binary system, the more massive star

answer

is nearest the center of mass.

question

The total mass of the pair of stars in spectroscopic binaries are difficult to estimate because

answer

we can't see the shape or tilt of the orbit.

question

Which star in Diagram 13-1 is most like the sun?

answer

HR 5337

question

Which star in Diagram 13-1 has the greatest surface temperature?

answer

Alnilam

question

Which of the stars in Diagram 13-1 has the largest absolute visual magnitude?

answer

Sirius B

question

An eclipsing binary will

answer

also be observed as a spectroscopic binary.

question

If we can solve the orbital motion of an eclipsing binary, we can find

answer

a. the mass of each star. b. the diameter of each star.

question

Which of the following kinds of stars best obey the mass-luminosity relation?

answer

main sequence stars

question

Which of the following kinds of stars is most dense?

answer

a white dwarf

question

A spectroscopic binary shows periodic variations in its

answer

radial velocity.

question

Stars on the main sequence with the greatest mass

answer

are spectral type O stars.

question

The total mass of a binary system can be calculated from

answer

the semi major axis and period of the orbit.

question

The diagram below illustrates two stars in a visual binary system and the center of mass of this system. Based on this diagram, what is the ratio of the mass of star A to the mass of star B?

answer

1 to 2

question

If a star has a parallax of 0.02 seconds of arc, then its distance is

answer

50 pc

question

If a star with an absolute magnitude of −5 has an apparent magnitude of +5, then its distance is

answer

1000 pc.

question

An eclipsing binary has been analyzed and it has been determined that the ratio of the mass of star A to the mass of star B is 6 and the total mass of the two stars is 26 solar masses. What are the masses of star A and star B?

answer

Star A has a mass of 22.3 solar mass and star B has a mass of 3.7 solar masses.

question

What is the total mass of a binary star system with P = 20 yr and a = 10 AU?

answer

2.5 solar masses

question

At what point in the light curve below is the cooler star in front of the hotter star?

answer

4

question

36. From the data given, which star in Table 13-1 would appear the faintest in the night sky?

answer

65 Tau

question

37. From the data given,, which star in Table 13-1 has the greatest luminosity?

answer

58 Ori

question

38. From the data given,, which star in Table 13-1 is the closest to Earth?

answer

HR 2491

question

39. From the data given,, which star in Table 13-1 has the greatest surface temperature?

answer

HR 4621

question

40. From the data given,, which star in Table 13-1 has the greatest diameter?

answer

58 Ori

question

41. Which star in Table 13-2 is the closest to Earth?

answer

9 CMa

question

42. Which star in Table 13-2 has the greatest surface temperature?

answer

δ Cen

question

43. Which star in Table 13-2 has the greatest diameter?

answer

HD 39801

question

If two stars are emitting the same amount of light, the star that is farther will appear

answer

dimmer.

question

We can determine the surface temperature of a star from

answer

a. studying its continuous spectrum. b. studying its line absorption spectrum. c. measuring the star's luminosity.

question

Which stars always have large positive absolute magnitude?

answer

Stars of low luminosity.

question

How can we tell that some stars are relatively close to us in the sky?

answer

Some stars appear to move periodically back and forth against the background stars because of the Earth's movement around the Sun.

question

The most accurate way to determine the surface temperature of a star is to study

answer

the pattern of absorption lines from various atoms.

question

If you compare two stars,

answer

the one with the smaller absolute magnitude will always have the greater luminosity.

question

Stars in the upper right part of the Hertzsprung-Russell diagram are always ____ when compared to stars near the middle of the diagram.

answer

larger

question

How is a luminosity class assigned to a star?

answer

By studying the absorption line width in the spectrum of the star.

question

As a main sequence star exhausts hydrogen in its core, its surface becomes ___ and its energy output per second (luminosity) becomes ____.

answer

cooler; larger

question

As a main sequence star exhausts hydrogen in its core, it next becomes

answer

a red giant star.

question

A star will experience a helium flash if

answer

a. it is less massive than about 3 solar masses. b. its has become a red giant star. c. its has formed a helium core. d. the material in the core has gradually become degenerate.

question

In degenerate matter

answer

pressure does not depend on temperature.

question

Giant and supergiant stars are rare because

answer

the giant or supergiant stage is very short.

question

A(n) ____ is a collection of 100 to 1000 stars in a region about 25 pc in diameter. The stars in the collection are typically quite young.

answer

open cluster

question

A(n) ____ is a collection of 105 to 106 stars in a region 10 to 30 pc in diameter. The stars in the collection tend to be more than 109 years old and mostly yellow and red stars.

answer

globular cluster

question

Stars within a cluster that are at the turnoff point

answer

have life expectancies that are equal to the age of the cluster.

question

In star clusters, the ____ stars are giant stars fusing helium in their cores and then in their shells.

answer

horizontal branch

question

In the orbital plane of a binary star system, matter can be transferred from one star to the other at the ________ located directly between the two stars is the point where the Roche lobes meet.

answer

Lagrangian points

question

A mass is transferred in a normal star in a binary system toward a white dwarf, the material forms a rapidly growing whirlpool of material known as a(n)

answer

accretion disk.

question

____ is a form of electromagnetic radiation produced by rapidly moving electrons spiraling through magnetic fields.

answer

Synchrotron radiation

question

The Crab nebula is

answer

supernova remnant.

question

Star clusters are important to our study of stars because

answer

they give us a method to test the our theories and models of stellar evolution.

question

What is the approximate age of the star cluster in the H-R diagram below? Hint: Main sequence stars of spectral types between A and B core's supply of hydrogen is sufficient to last about 250 million years. Between A and F about 2 billion years. Type G about 10 billion years. Between K and M about 30 billion years.

answer

10 billion years

question

The triple alpha process

answer

occurs during helium flash.

question

Which of the following nuclear fuels does a one-solar mass star use over the course of its entire evolution?

answer

hydrogen and helium

question

Helium flash occurs

answer

because degenerate electrons in the core do not allow the core to expand as it heats up.

question

Stars in a star cluster

answer

a. all have the same age. b. all have the same chemical composition.

question

If the stars at the turnoff point of a cluster have a mass of 3 M, what is the age of the cluster?

answer

6.4×10^8 years

question

In the diagram below, which point indicates the location on the H-R diagram of a one solar mass star when it undergoes helium flash?

answer

5

question

The lowest-mass stars cannot become giants because

answer

they cannot heat their centers hot enough.

question

A planetary nebula is

answer

the expelled outer envelope of a medium mass star.

question

The Chandrasekhar limit tells us that

answer

white dwarfs more massive than 1.4 solar masses are not stable.

question

A Type I supernova is believed to occur when

answer

a white dwarf exceeds the Chandrasekhar limit.

question

Massive stars cannot generate energy through iron fusion because

answer

both fusion or fission of iron nuclei absorb energy.

question

The theory that the collapse of a massive star's iron core produces neutrinos was supported by

answer

the detection of neutrinos from the supernova of 1987.

question

Synchrotron radiation is produced by

answer

high-velocity electrons moving through a magnetic field.

question

A nova is almost always associated with

answer

a white dwarf in a close binary system.

question

The Algol paradox is explained by considering

answer

mass transfer between the two stars in a binary system.

question

Stars with masses between 0.4 and 4

answer

undergo thermonuclear fusion of hydrogen and helium but never get hot enough to ignite carbon.

question

A type-II supernova

answer

c. is characterized by a spectrum that shows hydrogen lines. d. occurs when the iron core of a massive star collapses.

question

Synchrotron radiation is produced

answer

in supernova remnants.

question

When material expanding away from a star in a binary system reaches the Roche surface

answer

the material is no longer gravitationally bound to the star.

question

A white dwarf is composed of

answer

carbon and oxygen nuclei and degenerate electrons.

question

A planetary nebula

answer

produces an emission spectrum.

question

If the theory that novae occur in close binary systems is correct, then novae should

answer

repeat after some interval.

question

As a white dwarf cools its radius will not change because

answer

pressure does not depend on temperature for a white dwarf because the electrons are degenerate.

question

The diagram below shows a light curve from a supernova. How many days after maximum light did it take for the supernova to decrease in brightness by a factor of 100?

answer

150

question

A planetary nebula has a radius of 0.5 pc and is expanding at 20 km/sec. What is the approximate age of this planetary nebula? (1 pc is equal to 3×1013 km, and 1 year is equal to 3.15×107 seconds.)

answer

24,000 years

question

About how long will a 0.5 star spend on the main sequence?

answer

57 billion years

question

For a star of Sun-like mass, what is the last stage of the nuclear fusion?

answer

helium to carbon and oxygen

question

What are the two longest stages in the life of a one solar mass star?

answer

main sequence, white dwarf

question

What nuclear fusion mechanism does an isolated white dwarf use to generate energy?

answer

White dwarfs don't generate their own energy.

question

Stars that have ejected a planetary nebula eventually become

answer

white dwarfs.

question

After what evolutionary stage does a star become a white dwarf?

answer

Giant

question

Where are elements heavier than iron primarily produced?

answer

Supernovae

question

The explosion of a supernova typically leaves behind

answer

a shell of hot, expanding gas with a pulsar at the center.

Combo astronomy 1

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