Question 1

How do astronomers measure the properties of molecular clouds?

Accepted Answer

Astronomers measure the properties of molecular clouds through the emission lines of tracer molecules like CO₂, which are used to determine various properties such as temperature, density, and chemical composition. This method allows astronomers to gather detailed information about molecular clouds and their role in star formation.

Question 2

Which of the following lists the phases of the interstellar medium in order,from densest to least dense?

Accepted Answer

The correct order from densest to least dense is molecular clouds (densest, where stars are born), H I clouds (neutral hydrogen), H II regions (ionized hydrogen, around hot stars), warm interstellar medium (partially ionized gas), and coronal gas (very hot, low-density gas).

Question 3

Giant molecular clouds are typically:

Accepted Answer

Giant molecular clouds are hierarchical in nature, meaning that they have structure on a wide range of length scales. This is due to the turbulent nature of the interstellar medium in which they form. They are not typically spherical, are not dominated solely by magnetic fields, and are found in the galactic disk rather than the halo.

Question 4

Which of the following adjectives best describes the interstellar medium?

Accepted Answer

The interstellar medium is known to be turbulent, as it is constantly being stirred up by the movement of stars and the explosions of supernovae. This turbulence creates complex patterns of gas and dust that can be difficult to study, but which play a vital role in the formation and evolution of galaxies.

Question 5

Which of the following is an important effect of interstellar dust?

Accepted Answer

Interstellar dust provides a platform for the formation of molecules, including complex organic molecules. This is important for the development of life in the universe.

Question 6

What is the wavelength of radiation produced by the system in the figure below?

Accepted Answer

The answer of What is the wavelength of radiation produced...

Question 7

An interstellar gas cloud has a temperature of 100 K and a density of 50 particles per cubic centimeter.How could an astronomer most easily observe this cloud?

Accepted Answer

Atomic hydrogen absorption lines are the most easily observed because the cloud is cold and has a low density.

Question 8

A gas cloud is in pressure equilibrium with its surroundings,which have a temperature of 10⁴ K.If the gas cloud is 100 times denser than the surrounding medium,what is its temperature?

Accepted Answer

In pressure equilibrium, the pressure inside the gas cloud equals the pressure of the surroundings. Pressure is proportional to the product of density and temperature. If the gas cloud is 100 times denser, its temperature must be 100 times lower to maintain the same pressure, so the temperature is 100 K.

Question 9

How do dust particles affect the formation of interstellar molecules?

Accepted Answer

Dust particles can act as a surface for other atoms and molecules to react upon, creating larger and more complex molecules. The surface area of the dust particles provides a place for molecules to attach and react, leading to the formation of interstellar molecules. This process is known as adsorption.

Question 10

How are the properties of the densest parts of the interstellar medium measured?

Accepted Answer

The properties of the densest parts of the interstellar medium are usually measured using molecular lines as they provide information about the physical conditions and chemical composition of the gas.

Question 11

An interstellar gas cloud with a density of 100 particles per cubic centimeter and with a temperature of 100 K is in equilibrium with a medium with a density of 0.1 particles per cubic centimeter and 10⁶ K.What is the most likely explanation?

Accepted Answer

The answer of An interstellar gas cloud with a density...

Question 12

Which part of the interstellar medium is primarily photoionized?

Accepted Answer

The warm interstellar medium is primarily photoionized due to its high temperature and low density, which make it easier for photons to ionize atoms and molecules. Molecular clouds and H I clouds are less likely to be photoionized, as they contain denser and cooler gas, which requires higher-energy photons to ionize. Coronary gas refers to the outer atmosphere of a star, which is not part of the interstellar medium.

Question 13

What is the typical size of an interstellar dust grain?

Accepted Answer

Interstellar dust grains are typically very small, with sizes around 500 nanometers (0.5 microns). This size range allows them to contribute to the interstellar reddening and extinction of starlight as it passes through the dust-filled regions of space.

Question 14

Which of the following is a key constituent of the interstellar medium?

Accepted Answer

The key constituent of the interstellar medium is both gas and dust. The interstellar medium is a thin mixture of gases and dust that fills the space between stars. The gas is primarily composed of hydrogen and helium with trace amounts of other elements, while the dust is comprised of tiny particles including carbon, silicon, and other heavier elements. Together, these components make up the interstellar medium and play a crucial role in the formation and evolution of stars and galaxies.

Question 15

Which of the following provides the best example of turbulence?

Accepted Answer

Turbulence refers to chaotic, irregular fluid motion characterized by eddies and vortices. A molecular cloud with large whorls containing many smaller whorls is a classic example of turbulence, where the fluid (in this case, the gas in the cloud) exhibits chaotic and irregular motion on many scales.

Question 16

Which of the following phases of the interstellar medium is coldest?

Accepted Answer

Molecular clouds are the coldest phase of the interstellar medium, with temperatures as low as 10 K (-263°C). H I clouds have temperatures around 100 K, H II regions have temperatures around 10,000 K, and coronal gas has temperatures around 1,000,000 K.

Question 17

Which of the following is most strongly affected by interstellar dust?

Accepted Answer

Visible light is most strongly affected by interstellar dust, which can absorb and scatter this type of electromagnetic radiation, leading to phenomena such as the dimming and reddening of starlight as it passes through the dust.

Question 18

Which of the following molecules is the most abundant species in giant molecular clouds in the Milky Way?

Accepted Answer

H₂ (molecular hydrogen) is the most abundant molecule in giant molecular clouds, as these clouds are primarily composed of hydrogen.

Question 19

What is the best evidence that giant molecular clouds formed through collisions of large gas flows?

Accepted Answer

The Doppler shifts of segments of the clouds indicate varying velocities within the clouds, suggesting that they were formed through the dynamic process of collisions between large gas flows.

Question 20

What is the typical density of the interstellar medium?

Accepted Answer

The typical density of the interstellar medium is about 1 particle per cubic centimeter, which includes a mix of gas and dust particles.

Quiz 12: Nursery of the Stars: the Interstellar Medium and Star Formation