Consider the following pairs :
Objects in space: Description
- Cepheids: Giant clouds of dust and gas in space
- Nebulae: Stars which brighten and dim periodically
- Pulsars: Neutron stars that are formed when massive stars run out of fuel and collapse
How many of the above pairs are correctly matched?
Detailed Explanation:
Answer: Option 1 — Only one
This question tests the knowledge of celestial objects and their correct definitions. Out of the three pairs given, only the third pair (Pulsars) is correctly matched, while the first two pairs have their descriptions reversed.
❌ Pair 1 – Incorrect: Cepheids are not giant clouds of dust and gas; they are actually pulsating stars that brighten and dim periodically, making them important distance markers in astronomy.
❌ Pair 2 – Incorrect: Nebulae are not stars that brighten and dim periodically; they are giant clouds of dust and gas in space where stars are born or remnants of dead stars.
✅ Pair 3 – Correct: Pulsars are indeed rapidly rotating neutron stars formed when massive stars exhaust their nuclear fuel and collapse in supernova explosions, emitting regular pulses of radiation.
📝 Short Notes: Celestial Objects
| Celestial Object | Correct Description | Key Characteristics |
|---|---|---|
| Cepheids | Pulsating variable stars that brighten and dim periodically | Period-luminosity relationship makes them 'standard candles' for measuring cosmic distances; named after Delta Cephei |
| Nebulae | Giant clouds of dust and gas in space | Can be emission, reflection, or dark nebulae; sites of star formation (stellar nurseries) or remnants of dying stars |
| Pulsars | Rapidly rotating neutron stars | Emit regular pulses of electromagnetic radiation; formed from supernova explosions; extremely dense (teaspoon weighs billions of tons) |
| Quasars | Extremely luminous active galactic nuclei | Powered by supermassive black holes; among the most distant and luminous objects in the universe |
| Supernovae | Explosive death of massive stars | Can briefly outshine entire galaxies; create and disperse heavy elements; leave behind neutron stars or black holes |
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