USAAAO 2026, I кръг — Задача 30

• B

Solution: From the colors of the galaxies, Galaxy S (a spiral galaxy with blue spiral arms) contains a younger stellar population, while Galaxy E (an elliptical galaxy with no blue stars, only red stars) contains an older stellar population. From this, we can know:

(I) True. Planetary nebulae come from low/intermediate-mass stars, which exist in both young and old populations. Thus, we can find planetary nebulae in both galaxies.

(II) True. Blue spiral arms indicate the presence of short-lived, massive stars with a lot of gas around. This implies there is likely an ongoing star formation.

(III) False. Galaxy E consists primarily of old, red stars and generally lacks cold gas, making ongoing star formation unlikely.

(IV) True. Type II supernovae are more likely to be found in young populations as their blue, massive stars die quickly. Thus, Galaxy S is more likely to have a Type II supernova.

(V) False. Type Ia supernovae usually originate from white dwarfs in binary systems and can occur in both young and old stellar populations, so they are not exclusive to Galaxy E.

Answer: B