astronomy- chapter 15 quiz review

The average density of the interstellar medium is:

1 atom/cm3

A typical molecular cloud has a temperature of approximately:

10 K

Dust that is heated to 30 K will emit a blackbody spectrum that peaks at:

100 ym

The figures below show the spectrum of a star, along with five other spectra labeled A through E. Which one of the labeled spectra shows what the spectrum of that star would look like if it were viewed through a significant amount of interstellar dust?

D

Below are three pictures of the disk of the Milky Way, taken in three different wavelength ranges. Put the three pictures in order from shortest to longest wavelength.

II, III, I

What critical event transforms a protostar into a normal main-sequence star?

Nuclear fusion begins in the core.

An H II region signals the presence of:

all of the above

If you wanted to study regions where star formation is currently happening you could use:

all of the above

In the interstellar medium, molecules survive only in regions with:

all of the above

Molecular cloud cores are places where you might find:

all of the above

Where have astronomers observed the existence of planets?

all of the above

What happens as a protostar contracts?

all of the above are true

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

an astronaut would feel cold standing in the 10^6 K intercloud gas

An accretion disk forms around a collapsing protostar because infalling material must conserve:

angular momentum

A ___ is a failed star that shines primarily because of energy derived from its gravitational collapse rather than nuclear burning.

brown drawf

"Weather" in the interstellar medium is produced:

by supernovae and strong winds from luminous stars

Stars with a mass from 0.01 M to 0.08 M are very different from the Sun because they:

cannot successfully execute the proton-proton chain reactions

Of the following processes at work in molecular clouds, which is the one that inevitably dominates the clouds' evolution?

conservation of angular momentum

If you wanted to observe heavy elements in the interstellar medium, where would be the best place to look?

dust grains

For an object in hydrostatic equilibrium, if the temperature inside the object were to increase, the object would:

expand

When looking at the space between stars, what might you see?

gas

The source of energy for a contracting protostar comes from:

gravitational potential energy

If you could watch stars forming out of a gas cloud, which stars would form first?

high-mass stars

Brown dwarfs are considered failed stars because:

hydrogen fusion never begins in their cores

As a protostar evolves, its temperature:

increases due to the kinetic energy of infalling material

Magnetic fields inside a molecular cloud act to:

inhibit gravitational collapse

The red emission in the photo below is due to:

ionized hydrogen (H II region)

21-cm radiation is important because:

it allows us to study neutral hydrogen in the interstellar medium

What is the most likely explanation for the dark area in the image below?

it is a region with thick dust blocking the starlight coming from behind.

The most common types of stars in our galaxy are:

low-mass stars

Use Figure 1 to compete the following statement. A high-mass protostar remains roughly constant in ___ and increases in ___ as it follows its evolutionary track.

luminosity; temperature

A surprising fact about a 1 M protostar is that, even though nuclear reactions have not yet started in their cores, they are ___ than the Sun.

more luminous

Molecular clouds, which have temperatures of around 10 K, are best observed at ___ wavelengths.

radio

Warm ionized gas in the interstellar medium appears ___ when imaged in the optical region of the electromagnetic spectrum.

red

Interstellar clouds are:

regions where hydrogen tends to be denser than the surrounding gas

Because angular momentum must be conserved, as a gas cloud contracts due to gravity it will also:

spin faster

Use Figure 1 to complete the following statement. A low-mass protostar remains roughly constant in ___ and decreases in ___ as it follows its evolutionary track.

temperature; luminosity

When radiation from an object passes through the interstellar medium:

the object appears redder and dimmer

We detect neutral gas in the interstellar medium by looking for radiation at 21 cm that arises when:

the spin of an electron flips and aligns with the spin of a proton in a hydrogen atom