Question 18 from UPSC CSE 2024 - S&T

Question

Consider the following statements:
1. Giant stars live much longer than dwarf stars.
2. Compared to dwarf stars, giant stars have a greater rate of nuclear reactions.
Which one of the following is correct in respect of the above statements?

IASCODEX · Accepted Answer

Correct Option: D. Statement-I is incorrect, but Statement-II is correct

Strategy: - Analyze the interplay of star size, nuclear reaction rate, and lifespan.
- Recognize that larger (giant) stars consume fuel faster, leading to shorter lifespans despite greater mass.
- Identify and eliminate common misconceptions, such as an incorrect statement regarding giant stars' lifespans.
- Confirm the accuracy of statements about the higher nuclear reaction rate in giants to determine the correct option.

Key Info: Giant stars are stars with much greater mass and volume than the Sun and typical dwarf stars. Because of their large mass, they have much higher core pressure and temperature, leading to a much higher rate of nuclear fusion reactions relative to smaller, less massive (dwarf) stars. This heightened activity means that although they have much more fuel in total, they exhaust it far more quickly, drastically shortening their lifespans--millions of years as opposed to billions for dwarf stars.

Dwarf stars (like red dwarfs) are less massive and burn their nuclear fuel slowly, granting them much longer lifespans, potentially even hundreds of billions of years. The evolutionary end states of giant stars are dramatic, often involving supernova explosions, leaving behind neutron stars or black holes. The Hertzsprung-Russell diagram graphically represents the distinctions between giant and dwarf stars in luminosity and temperature.

Nuclear fusion--primarily hydrogen burning via the proton-proton chain (in dwarfs) or CNO cycle (in giants)--dictates both brightness and life cycle. In summary, the greater nuclear reaction rate in giant stars causes faster fuel consumption and a much shorter lifespan compared to dwarf stars.

IASCODEX · Answer

Option A: Both Statement-I and Statement-II are correct and Statement-II explains Statement-I

IASCODEX · Answer

Option B: Both Statement-I and Statement-II are correct, but Statement-II does not explain Statement-I

IASCODEX · Answer

Option C: Statement-I is correct, but Statement-II is incorrect

Consider the following statements: Giant stars live much longer than dwarf stars. Compared to dwarf stars, giant stars have a greater rate of nuclear reactions. Which one of the following is correct in respect of the above statements?

Consider the following statements:

Giant stars live much longer than dwarf stars.

Compared to dwarf stars, giant stars have a greater rate of nuclear reactions.
Which one of the following is correct in respect of the above statements?