1. What observational signature distinguishes a true microlensing planetary event from a binary-lens stellar system?
- A) A strong color change in the source star at peak magnification
- B) Persistent radial-velocity shifts following the event
- C) A repeating light-curve pattern due to orbital motion
- D) A short-duration, low-mass perturbation superimposed on the main lensing curve
Answer: ✅ :alphabet-white-d: A short-duration, low-mass perturbation superimposed on the main lensing curve
This brief anomaly is the hallmark of a planetary companion: a tiny gravitational “blip” riding on top of the primary lens light curve. Binary stars produce longer, more complex caustic structures, not the sharp, localized deviation caused by a planet.
2. In galaxy evolution, what does “inside-out quenching” describe?
- A) Gas inflows that trigger a central starburst before stabilizing the disk
- B) Star formation shutting down first in the galactic center, then moving outward
- C) AGN jets stripping gas exclusively from the outer halo
- D) A merger-induced reversal of metallicity gradients
Answer: ✅ :alphabet-white-b: Star formation shutting down first in the galactic center, then moving outward
Massive galaxies commonly exhaust or heat their central gas—often via AGN feedback—before the outer disk. This creates the characteristic pattern where the core becomes quiescent while star formation persists in larger radii.
3. In exoplanet demographics, the “radius valley” refers to:
- A) A dip in the occurrence rate between super-Earths and sub-Neptunes
- B) A region where planets are able to maintain stable atmospheres
- C) The minimum radius a rocky planet can have before tidal stripping occurs
- D) A measurement bias caused by incomplete transit sampling
Answer: ✅ :alphabet-white-a: A dip in the occurrence rate between super-Earths and sub-Neptunes
Survey data show a deficit of planets around ~1.5–2 Earth radii. Atmospheric loss processes—like photoevaporation or core-powered mass loss—tend to strip small planets or leave them puffy, naturally separating the populations.
4. In neutron star physics, the “crust-breaking” model for magnetar flares proposes that:
- A) Magnetic stresses exceed elastic limits, causing sudden cracking of the crust
- B) Pair-production cascades ignite runaway fusion at the poles
- C) Accretion disks collapse, releasing gravitational energy
- D) Rotational shear triggers convection and neutrino emission
Answer: ✅ :alphabet-white-a: Magnetic stresses exceed elastic limits, causing sudden cracking of the neutron star crust
Magnetars possess enormous magnetic fields. When their crust can no longer endure the strain, it fractures abruptly, releasing energy stored in twisted magnetic field lines and producing powerful X-ray and gamma-ray flares.
5. What physical process drives atmospheric escape in highly irradiated exoplanets via the “Parker wind” mechanism?
- A) Ion pickup by stellar wind magnetic fields
- B) Surface sputtering from micrometeorite impacts
- C) Cryovolcanic venting at the terminator line
- D) Thermal expansion causing a hydrodynamic outflow
Answer: ✅ :alphabet-white-d: Thermal expansion causing a hydrodynamic outflow
Intense stellar heating causes the upper atmosphere to expand and accelerate outward, transitioning into a continuous transonic wind. This Parker-type flow can strip significant mass from close-in planets over time.