Q. Consider the following statements:
- Statement-I: Giant stars live much longer than dwarf stars.
- Statement-II: Compared to dwarf stars, giant stars have a greater rate of nuclear reactions.
Which one of the following is correct with respect to the above statements? (UPSC Prelims 2024)
Answer:
Statement-1 is incorrect, but Statement-2 is correct
Notes: The correct answer is
[D] Statement-I is incorrect, but Statement-II is correct.
- Statement-I (Incorrect): Contrary to what their name might suggest, giant stars have much shorter lifespans than dwarf stars. While giant stars possess significantly more fuel (hydrogen), they consume it at a disproportionately faster rate. A massive star might live for only a few million years, whereas a small red dwarf star can live for trillions of years.
- Statement-II (Correct): Giant stars have immense gravitational pressure and higher core temperatures due to their massive size. This environment accelerates the rate of nuclear fusion (nuclear reactions). Because the pressure in the core is so high, they burn through their nuclear fuel with extreme intensity compared to the slower, more stable fusion found in dwarf stars.
Key Conceptual Fact: In stellar evolution, there is an inverse relationship between a star's mass and its lifespan. The "greater rate of nuclear reactions" mentioned in Statement-II is precisely the reason why Statement-I is false; the high reaction rate leads to rapid fuel exhaustion, resulting in a shorter life for giant stars.