
Concept explainers
Choose the best answer to each of the following. Explain your reasoning.
What shows down the contraction of a star-forming cloud when it makes a protostar? (a) production of fusion energy (b) magnetic fields (c) trapping of thermal energy inside the protostar.

The correct option for the cause that slows down the contraction of a star-forming cloud when it makes a protostar.
Answer to Problem 1QQ
Option (c) is the correct answer. Trapping of thermal energy inside the protostar slows down the contraction of a star-forming cloud.
Explanation of Solution
Introduction:
Protostar is a contracted mass of gases and it represents the early stage in the formation of a star. This phase starts when a fragment of cloud collapses under the gravitational forces and ends when a pre-main-sequence star is formed due to the depletion of in falling gas. This pre-main-sequence star later forms a main-sequence star.
During the formation of protostar, the thermal energy gets trapped inside the protostar. Also, the gravity results in the contraction of the protostar due to inward force. But the increase in thermal energy results in an increase of thermal pressure, which pushes the layers outward. Hence, contraction of star-forming cloud slows down.
Thus, option (c) is correct.
Option (a) is incorrect as no fusion energy is produced during the formation of protostar.
Option (b) is incorrect as there is reduction in magnetic fields.
Conclusion:
Hence, trapping of thermal energy inside the protostar slows down the contraction of a star-forming cloud when it makes a protostar.
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