Question 28 from UPSC CSE 2023 - S&T

Question

Consider the following pairs:
1. Cepheids - Giant clouds of dust and gas in space
2. Nebulae - Stars which brighten and dim periodically
3. Pulsars - Neutron stars that are formed when massive stars run out of fuel and collapse
How many of the above pairs are correctly matched?

IASCODEX · Accepted Answer

Correct Option: A. Only one

Strategy: Review each celestial pair to identify definitional mismatches. Cepheids are pulsating stars, not dust clouds (which describe nebulae). Only the description for 'Pulsars' as neutron stars from collapsed massive stars is accurate. Therefore, only one pair is correct.

Key Info: ## Cepheids (Cepheid Variables)
These are a class of pulsating variable stars whose brightness changes regularly over days to months. Their predictable relationship between luminosity and pulsation period makes them crucial "standard candles" for measuring cosmic distances.

## Nebulae
Vast, diffuse clouds composed of dust, hydrogen, helium, and other ionized gases in interstellar space. Nebulae can form from supernova explosions (supernova remnants) or act as active star-forming regions (stellar nurseries). Examples include the Orion Nebula and the Crab Nebula.

## Pulsars
Highly magnetized, rotating neutron stars that emit beams of electromagnetic radiation from their poles. They form after massive stars undergo a supernova explosion and their cores collapse into dense neutron stars. The observed pulses result from the neutron star's rotation, sweeping its emission beam across Earth at regular intervals.

IASCODEX · Answer

Option B: Only two

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Option C: All three

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Option D: None of the above statements is correct

Consider the following pairs: 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?

Consider the following pairs:

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?