Astronomy ch 15

We observe neutral hydrogen gas using

21-cm emission.

The figure below shows 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.

If you wanted to study regions where star formation is currently happening, you could look for

O and B stars.

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

Star formation occurs in dusty regions.

An H II region signals the presence of

all of these

Radio waves with 21-cm wavelengths are important because they

allow us to study neutral hydrogen in the interstellar medium.

As a protostar evolves towards becoming a main-sequence star, its core temperature will

always increase.

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

an astronaut would not burn up while floating in 106 K intercloud gas.

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

angular momentum.

The interstellar medium is divided into three different kinds of gas clouds. These are

cold gas at 100 K, warm gas at 8000 K, and hot gas at about 1 million K.

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 are you most likely to see?

gas

The thermal energy of a contracting protostar comes from

gravitational potential energy.

Brown dwarfs are considered failed stars because

hydrogen fusion never begins in their cores.

Molecular hydrogen atoms can be found

in dense clouds where they are shielded from stellar radiation.

As a protostar is evolving, its temperature

increases due to the kinetic energy of infalling material.

Magnetic fields inside a molecular cloud act to

inhibit gravitational collapse.

A young protostar is ________ than the Sun even though its surface temperature is ________.

more luminous; cooler.

Interstellar extinction refers to

not a

Electronic transitions from the H2 molecule are easily seen at

not e

Dust reddens starlight because it

preferentially affects light at visible and shorter wavelengths.

The entire process of star formation is an evolving balance between ________ and gravity.

pressure

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.

When radiation from an object passes through the interstellar medium,

the object appears redder and dimmer.

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

visible; infrared