Introduction to Topics

The question from the 69th BPSC Prelims (2023) focuses on Astronomy and Astrophysics, specifically the nature of pulsars, which is a part of the General Science syllabus in the BPSC exam. This topic tests candidates’ knowledge of celestial objects and their properties, a recurring theme in competitive exams due to the significance of space science in modern technology and scientific advancements. Pulsars, as fascinating astronomical phenomena, are relevant for understanding the universe’s structure and evolution, and such questions align with BPSC’s emphasis on scientific concepts with global and educational importance.

Question and Options

Question: In the universe, what are pulsars?
(A) A group of stars
(B) Rotating neutron stars
(C) Explosion of a star
(D) Radio waves emitted by a star

Explanation

This question assesses candidates’ understanding of pulsars, requiring them to distinguish between different astronomical phenomena. Pulsars are a specific type of celestial object, and the options include distractors that test knowledge of related concepts like star groups, stellar explosions, and radio emissions.

• A group of stars (A):
  • Analysis: A group of stars refers to entities like star clusters or galaxies, not pulsars. Pulsars are individual objects with unique characteristics, not collections of stars.
  • Conclusion: Incorrect, as pulsars are not groups of stars.
• Rotating neutron stars (B):
  • Analysis: Pulsars are rapidly rotating neutron stars, which are the collapsed cores of massive stars after a supernova explosion. They emit beams of radiation, often in the form of radio waves, from their magnetic poles. As they rotate, these beams sweep across space like a lighthouse, creating periodic pulses detectable from Earth, hence the name “pulsar” (pulsating star). Their rotation periods can range from milliseconds to seconds.
  • Conclusion: Correct, as pulsars are indeed rotating neutron stars.
• Explosion of a star (C):
  • Analysis: The explosion of a star is a supernova, a cataclysmic event marking the death of a massive star. While pulsars form as a result of a supernova (leaving behind a neutron star), they are not the explosion itself but the remnant.
  • Conclusion: Incorrect, as pulsars are not the explosion but the resulting neutron star.
• Radio waves emitted by a star (D):
  • Analysis: Pulsars emit radio waves as part of their pulsating behavior, but they are not the radio waves themselves. The radio waves are a byproduct of the rotating neutron star’s magnetic field and rapid rotation, not the definition of a pulsar.
  • Conclusion: Incorrect, as pulsars are the objects (neutron stars), not the emissions.
• Option Analysis:
  • (A) A group of stars: Incorrect, as pulsars are individual neutron stars, not star clusters.
  • (B) Rotating neutron stars: Correct, as pulsars are defined as rapidly rotating neutron stars emitting periodic radiation.
  • (C) Explosion of a star: Incorrect, as this describes a supernova, not a pulsar.
  • (D) Radio waves emitted by a star: Incorrect, as pulsars are the neutron stars, not the radio waves they emit.
• Key Misconceptions:
  • Candidates might confuse pulsars with supernovae (explosions) due to their connection (pulsars form post-supernova).
  • The term “radio waves emitted by a star” might mislead those unaware that pulsars are the source, not the emission itself.
  • The question’s moderate difficulty lies in requiring precise knowledge of pulsars’ nature amidst distractors related to stellar phenomena.

Correct Answer

Correct Answer: (B) Rotating neutron stars

• Reason: Pulsars are rapidly rotating neutron stars, formed from the remnants of massive stars after a supernova explosion, emitting periodic beams of radiation (often radio waves) due to their rotation and strong magnetic fields.

5 Probable Questions of Similar Difficulty

1. Question: What are neutron stars primarily composed of?
   • (A) Hydrogen and helium
   • (B) Neutrons
   • (C) Plasma
   • (D) Heavy metals
     Answer: (B) Neutrons
     Explanation: Neutron stars, like pulsars, are composed primarily of densely packed neutrons, formed from the collapsed core of a massive star.
2. Question: Which of the following phenomena is associated with pulsars?
   • (A) Gravitational waves
   • (B) Periodic radio pulses
   • (C) Gamma-ray bursts
   • (D) Solar flares
     Answer: (B) Periodic radio pulses
     Explanation: Pulsars emit periodic radio pulses due to their rotation, distinguishing them from other phenomena like gravitational waves or gamma-ray bursts.
3. Question: Which of the following correctly describes a supernova?
   • (A) A rotating neutron star
   • (B) A massive star explosion
   • (C) A group of stars orbiting a black hole
   • (D) Radio waves from a dying star
     Answer: (B) A massive star explosion
     Explanation: A supernova is the explosive death of a massive star, which can leave behind a neutron star (e.g., a pulsar), unlike the other options.
4. Question: What is the primary source of a pulsar’s pulsating appearance?
   • (A) Orbital motion around another star
   • (B) Rapid rotation of a neutron star
   • (C) Expansion of a star’s outer layers
   • (D) Emission of gravitational waves
     Answer: (B) Rapid rotation of a neutron star
     Explanation: Pulsars appear to pulse due to their rapid rotation, causing beams of radiation to sweep across Earth like a lighthouse.
5. Question: Which of the following celestial objects is a pulsar most closely related to?
   • (A) Black hole
   • (B) White dwarf
   • (C) Neutron star
   • (D) Red giant
     Answer: (C) Neutron star
     Explanation: Pulsars are a type of neutron star, distinguished by their rapid rotation and radiation emission, unlike black holes, white dwarfs, or red giants.

Key Words Explained in Short

• Pulsar: Rapidly rotating neutron star emitting periodic radiation pulses, often radio waves.
• Neutron Star: Dense remnant of a massive star’s core after a supernova, primarily composed of neutrons.
• Supernova: Explosive death of a massive star, often resulting in a neutron star or black hole.
• Radio Waves: Electromagnetic waves emitted by pulsars due to their magnetic fields and rotation.
• Magnetic Field: Strong field in neutron stars, responsible for directing radiation beams in pulsars.
• Rotation: Rapid spinning of pulsars, causing their pulsating appearance (milliseconds to seconds).
• Radiation Beams: Narrow streams of energy (e.g., radio waves) emitted from a pulsar’s magnetic poles.
• Stellar Remnant: Object left after a star’s death, like a neutron star (pulsar) or white dwarf.

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