UPSC Prelims 2024 Q32: Science & Technology – Space Technology & Astronomy
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?
- (a) Both Statement - I and Statement - II are correct and Statement - II explains Statement - I
- (b) Both Statement - I and Statement - II are correct, but Statement - II does not explain Statement - I
- (c) Statement - I is correct, but Statement - II is incorrect
- (d) Statement - I is incorrect, but Statement - II is correct
Answer: (d) Statement - I is incorrect, but Statement - II is correct
Explanation
Giant stars vs dwarf stars — lifespan
| Feature | Giant (massive) stars | Dwarf (small) stars |
|---|---|---|
| Mass | Many times the Sun | Up to about the Sun's mass or less |
| Core temperature and pressure | Very high | Lower |
| Rate of nuclear fusion | Very high — burn fuel extremely fast | Slow and steady |
| Lifespan | Short — a few million years | Long — billions to trillions of years |
| End | Supernova → neutron star or black hole | White dwarf (Sun-like) |
Statement I — incorrect. Giant stars live shorter lives, not longer.
Statement II — correct. Giant stars fuse hydrogen at a far greater rate.
In fact, Statement II is the very reason Statement I is false.
Answer: (d) Statement - I is incorrect, but Statement - II is correct.
Why each option is right or wrong
- (a) Incorrect. Statement I is false; massive stars burn out quickly.
- (b) Incorrect. Both are not correct; giants live shorter lives than dwarfs.
- (c) Incorrect. It is the reverse: Statement I is false and Statement II is true.
- (d) CORRECT. Giant stars have a faster fusion rate, so they die younger than dwarf stars.
Key point
Bigger star = faster fusion = shorter life. Red dwarfs can live trillions of years; giants only millions.
Remember
Giant stars fuse faster and live much shorter lives than dwarf stars.
Common mistakes
- Assuming more fuel means a longer life; giants burn fuel far faster than they gain from the extra mass.
- Confusing a red giant (a late stage of a Sun-like star) with a massive star from birth.
- Not seeing that Statement II actually disproves Statement I.
Exam tip
'Live fast, die young.' The most massive stars are the shortest-lived.
Sources
- NCERT Class XI — Physics, Ch 8 (Gravitation)
- NASA — Stars: life cycle (science.nasa.gov)