ASTR Chap 15 - Star Formation & the Interstellar Medium

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In protoplanetary environments, the plane of an accretion disk is perpendicular to the axis of rotation of the interstellar cloud out of which it forms.

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

Angular momentum

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

H-alpha emission to look for O and B stars
21 cm radiation to find neutral hydrogen clouds
Radio emission from carbon monoxide (CO) to find molecular cloud cores
Infrared emission to identify T Tauri stars

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

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 10^6 K intercloud gas

At which point in time does the collapsing cloud have the greatest angular momentum?

The cloud has the same angular momentum at each point in time.

If a collapsing interstellar cloud formed only a protostar without an accretion disk around it, what would happen?

The forming protostar would be rotating too fast to hold itself together.

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 space images?

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

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

visible; infrared

The red emission in the photo below is due to:

ionized hydrogen (H II region)

Molecular hydrogen atoms are found only inside dense clouds where they are shielded from stellar radiation.

We observe neutral hydrogen gas using 21-cm emission.

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:

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