Previous Year Question
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 in respect of the above statements?
Correct Answer: D
Detailed Solution
The lifetime of a star is not determined merely by the total amount of fuel available to it. It depends more importantly on how rapidly the star consumes that fuel.
Statement I is incorrect. Giant or high-mass stars possess more nuclear fuel than dwarf stars, but they consume that fuel at a disproportionately higher rate. Consequently, their lifetimes are relatively short. Some very massive stars survive for only a few million years, whereas low-mass stars can survive for billions or even trillions of years.
For example, the Sun is a yellow dwarf star and is expected to spend approximately 10 billion years in its main-sequence stage. In contrast, a very massive star may have a lifetime of only a few million years.
Statement II is correct. Because of their greater mass, giant stars have higher gravitational pressure and temperature in their cores. The higher core temperature causes hydrogen fusion and other nuclear reactions to proceed much faster than in dwarf stars. This is why massive stars are generally hotter, more luminous and produce energy at a much greater rate.
Thus, despite possessing more fuel, giant stars consume it rapidly. They have a higher rate of nuclear reactions but a shorter lifespan.