ASP MCQ 4 — Questions and Answers
Question 1: What is a pulsar?
- A rapidly rotating neutron star emitting beams of electromagnetic radiation (Correct answer)
- A variable star that pulses due to internal oscillations
- A quasar with periodic luminosity changes
- A white dwarf accreting material from a companion star
Correct answer: A rapidly rotating neutron star emitting beams of electromagnetic radiation
A pulsar is a highly magnetized, rapidly rotating neutron star whose beamed radiation sweeps past Earth like a lighthouse, producing regular pulses.
Question 2: In spectroscopy, what does the presence of dark absorption lines in a star's spectrum indicate?
- Regions of high temperature in the star's photosphere
- Elements in the star's atmosphere absorbing specific wavelengths (Correct answer)
- Interstellar dust blocking starlight
- Doppler shifts due to stellar rotation
Correct answer: Elements in the star's atmosphere absorbing specific wavelengths
Absorption lines form when cooler atmospheric gases absorb specific photon energies from the continuous spectrum emitted below, revealing the star's elemental composition.
Question 3: What is the approximate age of the universe according to current cosmological models?
- 4.6 billion years
- 10.0 billion years
- 13.8 billion years (Correct answer)
- 20.0 billion years
Correct answer: 13.8 billion years
Based on CMB observations and the Hubble constant, the universe is estimated to be approximately 13.8 billion years old.
Question 4: Which process produces the energy radiated by main sequence stars like our Sun?
- Nuclear fission of uranium
- Gravitational contraction (Kelvin-Helmholtz mechanism)
- Proton-proton chain fusion of hydrogen into helium (Correct answer)
- Carbon-nitrogen-oxygen (CNO) cycle alone
Correct answer: Proton-proton chain fusion of hydrogen into helium
In solar-mass stars, the proton-proton chain dominates, fusing hydrogen nuclei into helium and releasing enormous energy as photons and neutrinos.
Question 5: What is the event horizon of a black hole?
- The photon sphere where light orbits the black hole
- The boundary within which escape velocity exceeds the speed of light (Correct answer)
- The accretion disk surrounding the singularity
- The region where tidal forces destroy infalling matter
Correct answer: The boundary within which escape velocity exceeds the speed of light
The event horizon is the spherical surface around a black hole's singularity at which escape velocity equals the speed of light — nothing inside can escape.
Question 6: What is the Oort Cloud?
- A ring of asteroids between Mars and Jupiter
- A disk of icy bodies extending from Neptune to ~50 AU
- A distant spherical shell of cometary nuclei surrounding the solar system (Correct answer)
- A cloud of molecular hydrogen surrounding the Milky Way's core
Correct answer: A distant spherical shell of cometary nuclei surrounding the solar system
The Oort Cloud is a hypothetical distant shell of icy planetesimals extending to ~100,000 AU, thought to be the source of long-period comets.
Question 7: Which NASA mission first confirmed the existence of water ice at the lunar poles?
- Apollo 17
- Lunar Prospector
- Chandrayaan-1
- LCROSS (Correct answer)
Correct answer: LCROSS
The LCROSS mission (2009) deliberately impacted the lunar south pole and spectroscopically confirmed water ice in the debris plume.
