Astronomers believe that stars develop from the condensation of interstellar gas clouds (IGCs) that are initially hundreds to even thousands of times more massive than the Sun. Two astronomers discuss the star formation process in these clouds.Astronomer X:Star formation begins when large fragments of a gas cloud collapse. Each of these fragments typically contains hundreds of times more gas than exists in an individual star. This collapse occurs when the gravitational attraction between the gas particles overcomes the sum of all outward forces. When collapsing gas particles in each fragment get close together, heat builds up. As a protostar begins with the inward movement of particles from the exterior of the protostar. Its collapse stops when outward forces, especially forces that result from the heating of the gas being compressed, balance the gravitational force. This brings a small region of the original cloud into equilibrium and a new star into a stable form.Astronomer Y:Stars develop when small fragments of gas clouds collapse. Calculations show that when fragmentation occurs, the fragments that form are much smaller in size than mature stars. Thus, stars develop from relatively small masses and volumes of the large IGCs called cores. A cold core collapses because of its own gravity. However, 95% of all localized cores are called protostars. The collapse of a cold core is stopped by outward forces that develop when the gas heats up. The protostar then gravitationally attracts for outer layers of the cold core together until the gas has completely transformed into a star. At early stages in development, the outer layers of the cold core are so thick that they prevent the core's light from escaping into space. Only after the outer layers have been incorporated into the star does the star become visible.Which of the following hypotheses would Astronomer Y most likely make if a new star suddenly appeared in IGC?
Correct answer: B. A collapsing fragment of gas has become dense enough to begin shining
A. A cold core has incorporated its outer layers
B. A collapsing fragment of gas has become dense enough to begin shining
C. Reflected light from our sun is seen bouncing off the IGC
D. The force of gravity has joined several fragments of a collapsing cloud
Explanation
Astronomer Y's hypothesis would most likely be that a new star suddenly appeared in an IGC because a collapsing fragment of gas has become dense enough to begin shining. This aligns with the description provided by Astronomer Y, where stars develop from small fragments of gas clouds that collapse and form new stars when they become dense enough to shine. The other options do not accurately reflect the process of star formation as explained by Astronomer Y.
Last updated 3 September 2026

Question

Astronomers believe that stars develop from the condensation of interstellar gas clouds (IGCs) that are initially hundreds to even thousands of times more massive than the Sun. Two astronomers discuss the star formation process in these clouds.Astronomer X:Star formation begins when large fragments of a gas cloud collapse. Each of these fragments typically contains hundreds of times more gas than exists in an individual star. This collapse occurs when the gravitational attraction between the gas particles overcomes the sum of all outward forces. When collapsing gas particles in each fragment get close together, heat builds up. As a protostar begins with the inward movement of particles from the exterior of the protostar. Its collapse stops when outward forces, especially forces that result from the heating of the gas being compressed, balance the gravitational force. This brings a small region of the original cloud into equilibrium and a new star into a stable form.Astronomer Y:Stars develop when small fragments of gas clouds collapse. Calculations show that when fragmentation occurs, the fragments that form are much smaller in size than mature stars. Thus, stars develop from relatively small masses and volumes of the large IGCs called cores. A cold core collapses because of its own gravity. However, 95% of all localized cores are called protostars. The collapse of a cold core is stopped by outward forces that develop when the gas heats up. The protostar then gravitationally attracts for outer layers of the cold core together until the gas has completely transformed into a star. At early stages in development, the outer layers of the cold core are so thick that they prevent the core's light from escaping into space. Only after the outer layers have been incorporated into the star does the star become visible.Which of the following hypotheses would Astronomer Y most likely make if a new star suddenly appeared in IGC?

Correct answer: B. A collapsing fragment of gas has become dense enough to begin shining

A. A cold core has incorporated its outer layers
B. A collapsing fragment of gas has become dense enough to begin shining
C. Reflected light from our sun is seen bouncing off the IGC
D. The force of gravity has joined several fragments of a collapsing cloud

Explanation

Astronomer Y's hypothesis would most likely be that a new star suddenly appeared in an IGC because a collapsing fragment of gas has become dense enough to begin shining. This aligns with the description provided by Astronomer Y, where stars develop from small fragments of gas clouds that collapse and form new stars when they become dense enough to shine. The other options do not accurately reflect the process of star formation as explained by Astronomer Y.

Last updated 3 September 2026

TestUstad · Accepted Answer

A collapsing fragment of gas has become dense enough to begin shining. Astronomer Y's hypothesis would most likely be that a new star suddenly appeared in an IGC because a collapsing fragment of gas has become dense enough to begin shining. This aligns with the description provided by Astronomer Y, where stars develop from small fragments of gas clouds that collapse and form new stars when they become dense enough to shine. The other options do not accurately reflect the process of star formation as explained by Astronomer Y.

TestUstad · Answer

A cold core has incorporated its outer layers

TestUstad · Answer

Reflected light from our sun is seen bouncing off the IGC

TestUstad · Answer

The force of gravity has joined several fragments of a collapsing cloud

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