Astrophysics Chapter 18 Flashcards

Questions and Answers

The polarization of light passing through the dust grains shows that:

The dust grains are elongated in shape. (correct)

The dust grains are aligned by a weak interstellar magnetic field. (correct)

Why does the density of interstellar dust block starlight?

The dust particles are about the same size as the light waves they absorb.

What is the overall dimming of starlight by interstellar matter called?

extinction

Where are gas and dust found in the Milky Way galaxy?

everywhere Signup and view all the answers

Which is the least dense?

interstellar dust Signup and view all the answers

The relative density of dust to gas is least in which place?

the atmosphere of Earth Signup and view all the answers

Most interstellar clouds are:

much bigger than our solar system Signup and view all the answers

What feature of interstellar dust is inferred by the polarization of starlight?

its shape Signup and view all the answers

Emission nebulae like M42 occur only near stars that emit large amounts of:

ultraviolet radiation Signup and view all the answers

What is the primary visible color of an emission nebula?

red due to ionized hydrogen atoms Signup and view all the answers

The gas density in an emission nebula is typically about how many particles per cc?

hundred Signup and view all the answers

Interstellar gas is composed of:

90% hydrogen, 9% helium by weight Signup and view all the answers

Ionization of hydrogen in H II regions is most visible at:

656.3 nm, Balmer alpha line for 3-2 electron transition Signup and view all the answers

In which wavelengths have the births of new stars been best mapped recently?

infrared Signup and view all the answers

What two things are needed to create an emission nebula?

hot stars and interstellar gas, particularly hydrogen Signup and view all the answers

A large gas cloud in the interstellar medium that contains several type O and B stars would appear to us as:

an emission nebula Signup and view all the answers

What type of interstellar matter produces narrow absorption lines in spectra of stars?

neutral gas Signup and view all the answers

Which of these is NOT a consequence of dust in the interstellar medium?

red light from the emission nebulae Signup and view all the answers

Charles Messier mapped the night sky and identified many objects now known to be emission nebulae in his search for objects that might be confused with:

comets Signup and view all the answers

A 'fuzzy' dark or light patch in the sky is called a:

nebula Signup and view all the answers

A reflection nebula is caused by:

starlight scattered by dust particles Signup and view all the answers

What effect do even thin clouds of dust have on light passing through them?

It dims and reddens the light of all more distant stars. Signup and view all the answers

Astronomers use roman numerals to indicate the ionization state of a gas. Ionized hydrogen is indicated by which of the following symbols?

H II Signup and view all the answers

Unlike the ultraviolet photons originally emitted by the embedded stars of an emission nebula, the photons emitted by the recombination of electrons with atoms:

escape the nebula Signup and view all the answers

Emission nebulae take up about how much of the Milky Way galaxy?

1% Signup and view all the answers

Why are dark dust clouds largely misnamed?

They contain much more gas than dust. Signup and view all the answers

Interstellar absorption lines are narrow primarily because:

the matter is at a low temperature, and atoms are almost still. Signup and view all the answers

Which statement about dark nebulae is true?

They can be penetrated only with longer wavelengths such as radio and infrared. Signup and view all the answers

The average temperature of the typical dark dust cloud is about:

100 K Signup and view all the answers

Interstellar dust clouds are best observed at what wavelength?

Radio and infrared Signup and view all the answers

The Local Bubble was probably created by:

a nearby supernova perhaps 300,000 years ago, brighter than the full Moon. Signup and view all the answers

The 'Local Bubble' is:

about 100 pcs across and transparent to extreme ultraviolet radiation. Signup and view all the answers

The ________ of light passing through thin dust clouds lets us map the Galaxy's magnetic field.

polarization Signup and view all the answers

Study Notes

Interstellar Dust and Its Properties

Polarization of light through dust grains indicates that they are aligned by a weak interstellar magnetic field.
Interstellar dust has a very low density but still blocks starlight due to particles being similar in size to the light waves they absorb.
The overall dimming of starlight caused by interstellar matter is referred to as extinction.
Dust and gas are omnipresent in the Milky Way galaxy and contribute to its structure.

Characteristics of Interstellar Gas

Interstellar gas is primarily composed of 90% hydrogen and 9% helium by weight.
Most interstellar clouds are significantly larger than the solar system.
The gas density in emission nebulae, such as M42, often involves hundreds of particles per cubic centimeter.

Emission Nebulae

Emission nebulae occur near stars that emit substantial ultraviolet radiation, with red being the primary visible color due to ionized hydrogen atoms.
The formation of an emission nebula requires the presence of hot stars and interstellar gas, particularly hydrogen.
The Balmer alpha line (656.3 nm) is indicative of ionized hydrogen in H II regions.

Interstellar Medium Observations

New star births are best mapped in the infrared spectrum, while neutral gas produces narrow absorption lines in stellar spectra.
Emission nebulae comprise approximately 1% of the Milky Way galaxy.

Dark Dust Clouds

Dark dust clouds are somewhat misnamed as they contain significantly more gas than dust.
They can be observed in longer wavelengths like radio and infrared, with an average temperature around 100 K.

Light Interaction with Interstellar Medium

Even thin dust clouds can significantly dim and redden light from distant stars.
Starlight scattered by dust particles leads to the formation of reflection nebulae.

The Local Bubble

The Local Bubble, about 100 parsecs across, was likely formed by a nearby supernova approximately 300,000 years ago.
This region is transparent to extreme ultraviolet radiation and allows astronomers to map the Galaxy's magnetic field through light polarization.

Interstellar Radiation and Detection

21 cm radiation provides distribution information about gas clouds, effectively used for studying interstellar matter.

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Description

Explore key concepts related to interstellar dust and its impact on light polarization in this flashcard set. Gain insights into how dust shapes our understanding of astrophysical phenomena. Perfect for revising Chapter 18's essential topics in astrophysics.