1. What does the Chandrasekhar mass limit (~1.4 solar masses) represent in astrophysics?
- A) The maximum mass a neutron star can support before collapsing into a black hole
- B) The maximum mass a white dwarf can have before collapsing under its own gravity
- C) The minimum mass required for a star to begin nuclear fusion
- D) The maximum mass of a main sequence star before it becomes unstable
Answer: B) The maximum mass a white dwarf can have before collapsing under its own gravity
This limit, derived by Subrahmanyan Chandrasekhar, marks the threshold beyond which electron degeneracy pressure can no longer support a white dwarf. Exceeding it leads to collapse into a neutron star or a supernova.
2. What is the primary reason elliptical galaxies appear redder than spiral galaxies?
- A) They are dominated by older, cooler stars with little ongoing star formation
- B) They are farther away and redshifted due to cosmic expansion
- C) Their gas clouds emit strongly in the infrared
- D) They are obscured by intergalactic dust
Answer: A) They are dominated by older, cooler stars with little ongoing star formation
Elliptical galaxies lack significant interstellar gas, so new hot blue stars cannot form. Their light is dominated by long-lived, cooler red stars, giving them a reddish color.
3. In spectroscopy of exoplanet atmospheres, what is the significance of the sodium (Na) and potassium (K) absorption lines?
- A) They indicate the presence of liquid oceans on the planet’s surface
- B) They can be used to measure atmospheric temperature and pressure profiles
- C) They reveal strong magnetic fields surrounding the planet
- D) They show that the planet has a dense carbon dioxide atmosphere
Answer: B) They can be used to measure atmospheric temperature and pressure profiles
Strong Na and K absorption features in transmission spectra are indicators of atmospheric structure. Their line broadening reveals temperature, pressure, and even wind patterns.
4. What astrophysical reason explains why pulsar timing is so precise for detecting exoplanets?
- A) Pulsars emit regular gamma-ray flares that reflect off planets
- B) Pulsars emit beams of radio waves with incredibly stable rotational periods
- C) Pulsars are surrounded by accretion disks that amplify timing signals
- D) Pulsars experience minimal gravitational lensing from their host galaxies
Answer: B) Pulsars emit beams of radio waves with incredibly stable rotational periods
Pulsars are cosmic clocks. Even tiny deviations in their regular radio pulses can indicate the gravitational tug of orbiting planets, making this method one of the most precise for planet detection.
5. In cosmology, why is the cosmic microwave background (CMB) anisotropy crucial for modern astrophysics?
- A) It allows measurement of Earth’s orbital velocity around the Sun
- B) It provides evidence for stellar nucleosynthesis of heavy elements
- C) It encodes information about the universe’s initial density fluctuations and geometry
- D) It directly reveals the presence of exoplanet atmospheres in the early universe
Answer: C) It encodes information about the universe’s initial density fluctuations and geometry
Tiny temperature variations in the CMB are snapshots of early density fluctuations, which seeded galaxies and large-scale structure. They also constrain the curvature and composition of the universe.