Astronomy Chapter 20-21

A typical molecular cloud has a temperature of approximately

10K

The coldest molecular clouds in our galaxy have temperatures of approximately

10K

What is the most likely explanation for the dark area in the figure shown?

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

What happens as a protostar contracts?

Its density rises, Its temperature rises, Its radius decrease, Its pressure rises. (all of the above)

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

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

an astronaut would feel cold standing in the 10⁶ 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 dwarf

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

Which of the following traits does not help slow or prevent the collapse of a gas cloud?

high mass

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

high-mass stars

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

how the protostar's luminosity, temperature, and radius change with time.

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.

Dust in the ISM appears dark in _________ wavelengths and bright in _________ wavelengths.

infrared, visible

Magnetic fields inside a molecular cloud act to

inhibit gravitational collapse.

The most common types of stars in our galaxy are

low mass stars

Use the figure shown to complete the following statement. A high-mass protostar remains roughly constant in

luminosity, temperature

The average density of the interstellar medium is

much less dense than the best vacuum on Earth.

Dust reddens starlight because it

preferentially affects light at visible and shorter wavelengths.

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

pressure and gravity.

Molecular cloud cores are places where you might find

protostars, Herbig-Haro objects, molecular hydrogen (H2), carbon monoxide (CO). (all of the above)

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 the figure shown 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.

The dust in the interstellar medium comes primarily from

the stellar winds of main-sequence stars

What primarily makes it difficult to observe the process of star formation?

they occur in dusty regions