1. In exoplanet demographics, what does the “Neptune Desert” refer to?
- A) The scarcity of Neptune-mass planets very far from their stars
- B) The observed lack of short-period Neptune-size planets due to atmospheric loss
- C) A region where Neptune-mass planets cannot form because of disk fragmentation
- D) The inability of Neptune-like planets to migrate inward through resonances
Answer: B — The observed lack of short-period Neptune-size planets due to atmospheric loss
Neptune-mass planets that orbit very close to their stars tend to lose their atmospheres through intense photoevaporation, leaving behind rocky cores. This creates a real, well-known scarcity in parameter space.
2. What physical mechanism primarily drives tidal inflation in ultra-hot Jupiters?
- A) Heating from runaway molecular dissociation
- B) Ohmic dissipation from ionized winds interacting with the planetary magnetic field
- C) Surface tidal waves triggered by stellar granulation
- D) Core crystallization releasing latent heat
Answer: B — Ohmic dissipation from ionized winds interacting with the planetary magnetic field
At extreme temperatures (>1500–2000 K), atmospheric winds become partially ionized. As they move through the planet’s magnetic field, they generate electrical currents that dissipate as heat, puffing up the planet.
3. In galaxy evolution, what does “quenching (or strangulation)” most commonly describe?
- A) Rapid loss of dark matter halo mass in merging galaxies
- B) The cessation of star formation due to feedback or environmental stripping
- C) Neutral hydrogen cooling below 10 K and forming molecular clouds
- D) The collapse of a galaxy’s bar structure into a compact bulge
Answer: B — The cessation of star formation due to feedback or environmental stripping
Quenching stops new stars from forming—often through AGN feedback, supernova-driven outflows, or environmental processes such as ram-pressure stripping in galaxy clusters.
4. What is a key observational signature of a Class 0 protostar?
- A) Strong optical emission lines and an exposed stellar photosphere
- B) Dominant millimeter/sub-millimeter emission from a dense, deeply embedded envelope
- C) A large infrared excess but no molecular outflows
- D) Strong X-ray flares from a nearly mature stellar corona
Answer: B — Dominant millimeter/sub-millimeter emission from a dense, deeply embedded envelope
Class 0 objects are in the earliest, most obscured stage of star formation. Most of their energy is reprocessed by cold dust and emitted at long wavelengths, making them glow brightly in the sub-mm.
Bonus. In star formation, which phase marks the true beginning of a star’s life—when nuclear fusion first ignites and the object officially “turns on” as a newborn star?
- A) Protostar Phase
- B) Class 0 Collapse Phase
- C) Arrival on the Zero-Age Main Sequence (ZAMS)
- D) T Tauri Phase
Answer: C — Arrival on the Zero-Age Main Sequence (ZAMS)
The ZAMS marks the moment hydrogen fusion becomes self-sustaining in the core. From this point forward, the object is a true, newborn star stably burning hydrogen.