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Astronomy 110 Final Exam Questions with 100% correct answers | verified | latest update 2024
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Astronomy 110 Final ExamWhat happens to a low mass star after spending most of its life on the main sequence?
- ANS-It evolves to the red giant region of the H-R diagram.
Which two ways can a star generate energy? - ANS-Fusion reactions in the core of the
star and gravitational contraction.
How does a main sequence star become a red giant? - ANS-When H in the core is
exhausted, there is no more energy generation and gravity takes over, so the He core
and the surrounding H shell contract. This leads to H-fusion due to the heat created,
which releases energy at a higher rate than the core H-burning did, and the resulting
pressure lifts up the outer layers of the star so that the outer atmosphere balloons out to
a radius more than 100x larger, therefore decreasing the surface temperature.
What is the helium flash? - ANS-When a red giant is evolving, the point at which
He-fusion begins is called the "Helium Flash" because it is so rapid that it is actually
explosive.
What is required for He-fusion? - ANS-A higher core temperature
Stars in which phase occupy the Horizontal Branch on an H-R diagram? - ANS-Red
giants going into Helium Flash
How does a star evolve to a red supergiant? - ANS-When the 4He is used up, the star is
left with a C core, which will contract and get hotter, leading to He shell-fusion. The star
then expands again to become a Red Supergiant.
How can you measure the age of clusters? - ANS-If you know the Main Sequence
lifetimes of stars, you can estimate the age of the cluster by noting the masses of the
stars that are just evolving off the M-S.
What are planetary nebulas? - ANS-When a star is going through the triple-alpha
process, the burning rate becomes unstable and makes the stellar atmosphere expand
and contract (pulsate). With each pulsation, the outer part of the stellar atmosphere is
blown by radiation out into space, which results in a planetary nebula.
For high-mass stars, what provides energy generation? - ANS-CNO cycle
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