Question 1

What is a planetary nebula?

Accepted Answer

A planetary nebula is a glowing shell of gas and plasma ejected from a low-mass star in the final stage of its life, not from planets or a high-mass star. The ejection of material occurs when the star exhausts its nuclear fuel and begins to shed its outer layers, eventually forming a dense core known as a white dwarf. The gas in the planetary nebula is illuminated by the ultraviolet radiation from the hot core, causing it to glow with a variety of colors and shapes.

Question 2

Algol consist of a 3.7 MSᵤn main-sequence star and a 0.8 MSᵤn subgiant.Why does this seem surprising,at least at first?

Accepted Answer

The two stars in a binary system are expected to be the same age, so it's surprising that the less massive star is a subgiant while the more massive star is still on the main sequence, as more massive stars evolve faster.

Question 3

In order to predict whether a star will eventually fuse oxygen into a heavier element,what do you need to know about the star?

Accepted Answer

The fusion process of oxygen into a heavier element is only possible in stars with sufficient mass (usually at least 8 times the mass of the Sun). Therefore, the most important factor in predicting whether a star will undergo oxygen fusion is its mass.

Question 4

After a supernova explosion,the remains of the stellar core

Accepted Answer

After a supernova explosion, the remains of the stellar core can be either a neutron star or a black hole, depending on the mass of the original star. Stars with lower mass (<3 solar masses) will become white dwarfs, stars with moderate mass (3-8 solar masses) will become neutron stars, and stars with higher mass (>8 solar masses) will become black holes. Therefore, it is not always true that the remnant will be a neutron star, black hole, or white dwarf, hence options A and C are incorrect. Option D is true for the various types of stars that result from different mass ranges, but it is not correct regarding the specific remains of the stellar core after a supernova explosion.

Question 5

What is a helium flash?

Accepted Answer

Helium flash is the sudden onset of helium fusion in the core of a low-mass star. It happens when the core temperature becomes hot enough for helium fusion to occur, but the pressure is not yet high enough to support the core against gravitational collapse. This causes a rapid increase in temperature and pressure, which ignites helium fusion and leads to a burst of energy known as the helium flash.

Question 6

The main source of energy for a star as it grows in size to become a red giant is

Accepted Answer

As a star grows in size and its core temperature decreases, hydrogen fusion in the core slows down. However, the outer layers continue to contract, increasing the pressure and temperature of the surrounding layer of hydrogen. Eventually, this leads to hydrogen fusion in a shell surrounding the central core, providing the star with the energy it needs to continue expanding into a red giant.

Question 7

What is the CNO cycle?

Accepted Answer

The CNO cycle (Carbon-Nitrogen-Oxygen cycle) is a set of nuclear fusion processes by which four hydrogen nuclei (protons) are combined into one helium nucleus, with carbon, nitrogen, and oxygen acting as catalysts in the process. This cycle plays a crucial role in stars more massive than the Sun.

Question 8

Which of the following stars will certainly end its life in a supernova?

Accepted Answer

Only stars with a mass greater than about 8 solar masses have enough mass to undergo a supernova explosion. Therefore, a 10 solar mass star will certainly end its life in a supernova. The Sun will become a red giant, but will not have enough mass to become a supernova. Neutron stars are the remains of supernova explosions and do not themselves undergo supernovae.

Question 9

What happens when a main-sequence star exhausts its core hydrogen fuel supply?

Accepted Answer

When a main-sequence star exhausts its core hydrogen fuel supply, the core begins to shrink due to the lack of energy production, causing the outer layers of the star to expand. This expansion can increase the star's luminosity and causes it to become a red giant.

Question 10

Which of the following stars will live longest?

Accepted Answer

The length of a star's life is determined by how long it can fuse hydrogen into helium in its core, and this is primarily determined by its mass. Smaller stars like the 1-solar-mass star will have a longer lifespan because they burn their hydrogen fuel more slowly and efficiently than larger stars. The larger the star, the faster it burns through its fuel and the shorter its lifespan.

Question 11

Which of the following pairs of atomic nuclei would feel the strongest repulsive electromagnetic force if you tried to push them together?

Accepted Answer

Helium nuclei (with two protons) would experience the strongest repulsive electromagnetic force when pushed together, as the force is proportional to the product of the charges of the two nuclei. Helium has more protons (and thus a higher charge) than hydrogen or deuterium, leading to a stronger repulsion between two helium nuclei.

Question 12

In the context of understanding stellar lives,"high-mass" stars have masses

Accepted Answer

High-mass stars have masses greater than about 8 times the mass of our Sun. This is because stars with higher masses have more internal pressure and temperature, allowing them to burn their fuel faster and leading to shorter lifetimes.

Question 13

Which of the following lists the stages of life for a low-mass star in the correct order?

Accepted Answer

This is the correct order of the stages in the life of a low-mass star. The star begins as a protostar, becomes a main-sequence star, then a red giant, followed by a planetary nebula, and finally ends its life as a white dwarf.

Question 14

How are low-mass red giant stars important to our existence?

Accepted Answer

Low-mass red giant stars play a crucial role in the cosmic production of carbon, one of the essential elements for life as we know it. During their red giant phase, these stars undergo a process known as helium fusion or the triple-alpha process, where three helium nuclei are combined to form carbon. This process significantly contributes to the carbon abundance in the universe, including the carbon atoms found in our bodies.

Question 15

An H-R diagram for a globular cluster will show a horizontal branch-a line of stars above the main-sequence but to the left of the subgiants and red giants.Which of the following statements about these horizontal branch stars is true?

Accepted Answer

Horizontal branch stars generate energy through both hydrogen shell burning around an inert helium core and helium fusion in the core itself. This dual process is characteristic of their phase in stellar evolution.

Question 16

Why is Supernova 1987A particularly important to astronomers?

Accepted Answer

Supernova 1987A is particularly important to astronomers because it is the nearest supernova to have occurred at a time when we were capable of studying it carefully with telescopes. Its close proximity allowed for detailed observations and measurements of the explosion and its aftermath, providing valuable insights into the physics of supernovae and the properties of the interstellar medium.

Question 17

The ultimate fate of our Sun is to

Accepted Answer

Our Sun, being a relatively small star, is not massive enough to undergo a supernova explosion, nor will it become a neutron star or black hole. Instead, it will eventually use up all of its fuel and expand into a red giant, shedding its outer layers and leaving behind a hot, dense core known as a white dwarf. This core will slowly cool over time, eventually becoming a cold, black object known as a black dwarf. Therefore, the best choice is B.

Question 18

Why is iron significant to understanding how a supernova occurs?

Accepted Answer

Iron is significant because it marks a turning point in the life cycle of a star. When a star starts to fuse iron in its core, it no longer gains energy from the fusion process because iron fusion consumes more energy than it releases. This lack of energy release leads to the star's collapse and the subsequent supernova explosion.

Question 19

The overall helium fusion reaction is

Accepted Answer

The overall helium fusion reaction, also known as the triple-alpha process, involves three helium-4 nuclei (alpha particles) coming together to form one carbon-12 nucleus. This process is crucial in the evolution of stars, allowing them to create elements heavier than helium.

Question 20

Which low-mass star does not have fusion occurring in its central core?

Accepted Answer

When a low-mass star exhausts its hydrogen fuel in its core and becomes a red giant, the core contracts and heats up, allowing hydrogen fusion to continue in a surrounding shell. However, a red giant does not have fusion occurring in its central core.

Quiz 17: Star Stuff