Podcast
Questions and Answers
The polarization of light passing through the dust grains shows that:
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?
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?
What is the overall dimming of starlight by interstellar matter called?
extinction
Where are gas and dust found in the Milky Way galaxy?
Where are gas and dust found in the Milky Way galaxy?
Which is the least dense?
Which is the least dense?
The relative density of dust to gas is least in which place?
The relative density of dust to gas is least in which place?
Most interstellar clouds are:
Most interstellar clouds are:
What feature of interstellar dust is inferred by the polarization of starlight?
What feature of interstellar dust is inferred by the polarization of starlight?
Emission nebulae like M42 occur only near stars that emit large amounts of:
Emission nebulae like M42 occur only near stars that emit large amounts of:
What is the primary visible color of an emission nebula?
What is the primary visible color of an emission nebula?
The gas density in an emission nebula is typically about how many particles per cc?
The gas density in an emission nebula is typically about how many particles per cc?
Interstellar gas is composed of:
Interstellar gas is composed of:
Ionization of hydrogen in H II regions is most visible at:
Ionization of hydrogen in H II regions is most visible at:
In which wavelengths have the births of new stars been best mapped recently?
In which wavelengths have the births of new stars been best mapped recently?
What two things are needed to create an emission nebula?
What two things are needed to create an emission nebula?
A large gas cloud in the interstellar medium that contains several type O and B stars would appear to us as:
A large gas cloud in the interstellar medium that contains several type O and B stars would appear to us as:
What type of interstellar matter produces narrow absorption lines in spectra of stars?
What type of interstellar matter produces narrow absorption lines in spectra of stars?
Which of these is NOT a consequence of dust in the interstellar medium?
Which of these is NOT a consequence of dust in the interstellar medium?
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:
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:
A 'fuzzy' dark or light patch in the sky is called a:
A 'fuzzy' dark or light patch in the sky is called a:
A reflection nebula is caused by:
A reflection nebula is caused by:
What effect do even thin clouds of dust have on light passing through them?
What effect do even thin clouds of dust have on light passing through them?
Astronomers use roman numerals to indicate the ionization state of a gas. Ionized hydrogen is indicated by which of the following symbols?
Astronomers use roman numerals to indicate the ionization state of a gas. Ionized hydrogen is indicated by which of the following symbols?
Unlike the ultraviolet photons originally emitted by the embedded stars of an emission nebula, the photons emitted by the recombination of electrons with atoms:
Unlike the ultraviolet photons originally emitted by the embedded stars of an emission nebula, the photons emitted by the recombination of electrons with atoms:
Emission nebulae take up about how much of the Milky Way galaxy?
Emission nebulae take up about how much of the Milky Way galaxy?
Why are dark dust clouds largely misnamed?
Why are dark dust clouds largely misnamed?
Interstellar absorption lines are narrow primarily because:
Interstellar absorption lines are narrow primarily because:
Which statement about dark nebulae is true?
Which statement about dark nebulae is true?
The average temperature of the typical dark dust cloud is about:
The average temperature of the typical dark dust cloud is about:
Interstellar dust clouds are best observed at what wavelength?
Interstellar dust clouds are best observed at what wavelength?
The Local Bubble was probably created by:
The Local Bubble was probably created by:
The 'Local Bubble' is:
The 'Local Bubble' is:
The ________ of light passing through thin dust clouds lets us map the Galaxy's magnetic field.
The ________ of light passing through thin dust clouds lets us map the Galaxy's magnetic field.
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.
