Question 1

The Horsehead Nebula in Orion (see Figure 11-3 in Comins,Discovering the Essential Universe,6th ed.)is a distinct dark region surrounded by brighter regions.The Horsehead is an example of a(n):

Accepted Answer

The distinct dark region surrounded by brighter regions is a characteristic feature of a dark nebula. The Horsehead Nebula is an example of a dark nebula, as it is a dense cloud of gas and dust that blocks the light from behind it.

Question 2

What radiation ionizes the hydrogen in an emission nebula (H II region)?

Accepted Answer

Ultraviolet radiation from O and B stars is known to ionize the hydrogen in an emission nebula (H II region). These massive and hot stars emit a significant amount of ultraviolet radiation which is energetic enough to ionize the hydrogen atoms in the nebula, leading to the emission of light seen by astronomers as the characteristic red glow of H II regions.

Question 3

What is an emission nebula (H II region)? See Figure 11-3 in Comins,Discovering the Essential Universe,6th ed.

Accepted Answer

An emission nebula, also known as an H II region, is a region of ionized hydrogen gas that emits light due to the presence of one or more hot O- and B-type stars in the region. These stars emit large amounts of ultraviolet radiation that ionize the surrounding gas, causing it to glow. The ionized hydrogen gas is denoted by the symbol H II, where the Roman numeral II represents the fact that the hydrogen atoms have lost their electrons and are ionized. The emission nebulae are some of the most photogenic objects in the night sky and are often referred to as H II regions because the ionized hydrogen gas is the prominent feature of these objects.

Question 4

How do massive stars normally end their lives?

Accepted Answer

Massive stars normally end their lives through a massive explosion known as a supernova, which can briefly outshine an entire galaxy. This explosion leaves behind a remnant like a neutron star or a black hole.

Question 5

New stars are formed from:

Accepted Answer

New stars are formed from huge, cool dust and gas clouds that collapse under their own gravity, forming a protostar. As the protostar gathers more matter and becomes denser, nuclear fusion reactions begin at its core, producing energy and light. Eventually, the star stabilizes and reaches a state of equilibrium. This process of star formation is known as gravitational collapse.

Question 6

Evidence of massive amounts of hydrogen gas surrounding some stars comes from:

Accepted Answer

The observation of emission of characteristic red Balmer light from nebulosity around them is a clear indication of the presence of massive amounts of hydrogen gas. This is because the Balmer series of hydrogen emission lines lies in the visible range, and is excited through collisions with high-energy particles. Therefore, the detection of Balmer emission lines indicates the presence of hydrogen gas, which is being ionized by the radiation from the nearby stars.

Question 7

Long-exposure color photographs of the night sky often show regions that glow red,such as the Rosette Nebula in Figure 11-6 of Comins,Discovering the Essential Universe,6th ed.This distinctive red color is caused by the:

Accepted Answer

The distinctive red color in long-exposure color photographs of the night sky is caused by the ionization and subsequent recombination of hydrogen atoms in the Rosette Nebula. This process emits red light, which can be captured in the photograph.

Question 8

Open clusters are not:

Accepted Answer

Open clusters are gravitationally bound groups of stars, so option A is incorrect.

Answer: C
 Open clusters are formed from the same giant molecular cloud, so they are associated with other stars. Therefore, option C is incorrect.

Answer: D
 Open clusters typically contain fewer than a few hundred stars. Therefore, option D is also incorrect.

The correct answer is B: Open clusters are the result of star formation within a single giant molecular cloud.

Question 9

What causes the characteristic blue color of a reflection nebula?

Accepted Answer

The characteristic blue color of a reflection nebula is caused by the scattering of starlight from dust grains in the nebula. Blue light has a shorter wavelength than red light and is scattered more easily by the small dust grains, causing the nebula to appear blue.

Question 10

The distinct blue color of the nebulosity around stars in young clusters such as the Pleiades (see Figure 11-2,Comins Discovering the Essential Universe,6th ed.)is caused by:

Accepted Answer

The blue color is due to starlight being scattered and reflected by small dust grains in the interstellar material, which is more effective at shorter (blue) wavelengths.

Question 11

The bright stars at the center of an emission nebula (H II region)are:

Accepted Answer

The bright stars at the center of an emission nebula are typically young, massive stars of spectral type O and B, which emit large amounts of ultraviolet radiation that ionizes the surrounding gas and causes it to glow. These stars are short-lived and are thought to be responsible for much of the chemical enrichment in the galaxy. Red supergiants are older and less luminous stars, while hot white dwarfs are the remnants of stars that have already gone through their main sequence evolution. T Tauri stars are young stars that have not yet reached the main sequence and are not typically found in H II regions.

Question 12

Which statement about open star clusters is TRUE?

Accepted Answer

The motions of individual stars in open clusters cause them to eventually disperse. This is due to interactions with other stars and the gravitational influence of the Milky Way galaxy. While some may merge into larger clusters, the majority will eventually become unbound and scatter throughout the galaxy. Option A is incorrect as open star clusters do not transform into globular clusters. Option B is incorrect as supernova explosions are rare events and do not typically occur in open clusters. Option C is incorrect as open clusters do not have enough mass to condense into spiral galaxies.

Question 13

A reflection nebula is made visible by:

Accepted Answer

A reflection nebula is made visible by blue light preferentially scattered by dust grains. As the light from embedded stars passes through a cloud of dust, the blue light is scattered more efficiently than the other colors, making the nebula visible as a blue haze. The dust does not emit its own light, but instead reflects and scatters the light from the stars behind it.

Question 14

The distinctive color of a reflection nebula is:

Accepted Answer

The distinctive color of a reflection nebula is blue, caused by the scattering of light from dust grains.

Question 15

The MOST likely places in which stars and planetary systems are forming in the universe are:

Accepted Answer

Nebulae composed of gas and dust are the most likely places in which stars and planetary systems are forming. These nebulae, also known as stellar nurseries, provide the necessary materials for the formation of stars and planets. The gas and dust in these nebulae are pulled together by gravity, eventually forming dense clumps that ignite as stars.

Question 16

The energy required to ionize the hydrogen gas in an emission nebula (H II region)comes from:

Accepted Answer

The ionization of hydrogen gas in an emission nebula is primarily caused by the intense UV radiation emitted by the hot O and B stars within the nebula. These stars have very high surface temperatures and emit a large amount of energy in the form of UV radiation, which is absorbed by the surrounding gas, ionizing its atoms and creating the characteristic emission lines observed in H II regions. Supernovae, collisions between gas clouds, and T Tauri stars can also contribute to ionization in some cases, but they are not the primary source of energy in H II regions.

Question 17

There are several mechanisms that can trigger star formation in a cold,dark nebula.In each mechanism,the key to star formation is:

Accepted Answer

Compressing the gas and dust is the key to star formation, as it allows for gravitation to overcome the gas pressure and initiate the collapse of the cloud into a protostar. Ultraviolet radiation, heating the gas, and intense magnetic fields can all contribute to the process but they are not the primary triggers of star formation.

Question 18

What is the ultimate fate of an open star cluster?

Accepted Answer

An open star cluster is a loosely bound system of stars held together by gravitational attraction. As the cluster ages, its stars gradually disperse and escape the cluster's gravity, eventually leaving the cluster completely disbanded. This process can take millions or billions of years, depending on the initial size and density of the cluster. Therefore, the ultimate fate of an open star cluster is for its stars to escape one by one until the cluster no longer exists.

Question 19

Where are emission nebulae (H II regions)found?

Accepted Answer

Emission nebulae, also known as H II regions, are found around hot stars. These stars emit high-energy ultraviolet radiation, which ionizes the surrounding gas in the nebula, causing it to emit light in the visible spectrum. Therefore, emission nebulae are typically found in areas of active star formation, such as in spiral arms of galaxies, in nebulae, and in young open clusters.

Question 20

In photographs,the Pleiades open star cluster is surrounded by a bluish haze (see Figure 11-2,Comins,Discovering the Essential Universe,6th ed.).What causes this blue light?

Accepted Answer

The bluish haze seen in photographs of the Pleiades star cluster is caused by starlight being scattered by interstellar dust within the cluster. This scattered light appears blue due to Rayleigh scattering, which causes shorter wavelength light (blues and greens) to scatter more easily than longer wavelength light (reds and yellows).

Quiz 11: The Lives of the Stars From Birth Through Middle Age

The Horsehead Nebula in Orion (see Figure 11-3 in Comins,Discovering the Essential Universe,6th ed.) is a distinct dark region surrounded by brighter regions.The Horsehead is an example of a(n) :

What radiation ionizes the hydrogen in an emission nebula (H II region) ?

What is an emission nebula (H II region) ? See Figure 11-3 in Comins,Discovering the Essential Universe,6th ed.