Chapter 17: Astronomy

Which of the following stars will live longest?

1 solar mass star

According to the diagram, the approximate abundance of oxygen atoms in the galaxy is __________.

1/1000 that of hydrogen

Suppose that the star Betelgeuse (the upper left shoulder of Orion) were to supernova tomorrow (as seen here on Earth). What would it look like to the naked eye?

Betelgeuse would remain a dot of light, but would suddenly become so bright that, for a few weeks, we'd be able to see this dot in the daytime.

What element(s) should you expect to be most abundant in the star when it reaches Stage 6?

Carbon At Stage 6 the star has become a white dwarf, which is essentially the leftover core after all fusion has ceased. Because the last stage of fusion was helium fusion, in which helium fuses to make carbon, the white dwarf should be composed largely of carbon. (Some oxygen can also be produced during the late stages of helium fusion, so white dwarfs are often made of both carbon and oxygen.)

The star expels its outer layers into space almost immediately upon the end of Stage _____.

During Stage 5 the star has an inert carbon core surrounded by shells of helium and hydrogen fusion. Because the core will never become hot enough for carbon fusion, this is the last stage of the star's life, and at the end of this stage it expels its outer layers as a planetary nebula.

Why is a 1 solar-mass red giant more luminous than a 1 solar-mass main sequence star?

Fusion reactions are producing energy at a greater rate in the red giant.

Which of the following types of data provide evidence that helps us understand the life tracks of low-mass stars?

H-R diagrams of globular clusters

According to current understanding, the two most abundant elements in the universe were made __________.

In the big bang

Why is iron significant to understanding how a supernova occurs?

Iron cannot release energy either by fission or fusion.

Which of the following describes a star with a hydrogen-burning shell and an inert helium core?

It is a subgiant that grows in luminosity until helium fusion begins in the central core.

Where does gold (the element) come from?

It is produced during the supernova explosions of high-mass stars.

How do the properties of long-lived stars compare to those of short-lived stars?

Long-lived stars begin their lives with less mass and a smaller amount of hydrogen fuel. Long-lived stars are less luminous during their main-sequence lives.

Tidal forces are very important to the Algol system today, but were not important when both stars were still on the main sequence. Why not?

Main sequence stars in a system like the Algol system are small compared to their physical separation.

Which is more common: a star blows up as a supernova, or a star forms a planetary nebula/white dwarf system?

Planetary nebula formation is more common.

Consider the six stages labeled on (Figure 1) at left, showing the life track of a one-solar-mass star. During which of the labeled stages is the star generating energy through hydrogen fusion in its central core?

Stage 1 is the star's hydrogen-fusing, main-sequence stage.

Which statement accurately describes the length of Stage 1 compared to Stages 2 through 5? (Ignore Stage 6 for this question.)

Stage 1 lasts nearly 10 times as long as Stages 2 through 5 combined.

During which of the labeled stages on (Figure 1) at left, is the star generating energy through helium fusion in its central core (along with hydrogen fusion in a surrounding shell)?

Stage 4 is the star's helium core-fusion stage, when it generates energy both from helium fusion in the central core and hydrogen fusion in a surrounding shell.

If stars A and B are both main-sequence stars and star A has a greater fusion rate than star B, which of the following statements hold(s)?

Star A must be more luminous than star B. Star A must be more massive than star B.

In Part D, you saw that elements with even atomic numbers tend to be more abundant than neighboring elements with odd atomic numbers. What nuclear process explains why this is the case?

Starting from carbon (atomic number is 6), the most common nuclear reactions involve the fusion of an additional helium nucleus.

The observational data for the element abundances agree quite well with what we expect based on our current understanding of nuclear fusion and stellar evolution. But imagine the data had turned out to be different. Which of the following differences, if it had actually been observed, would have forced us to rethink our entire picture of stellar evolution?

The abundance of elements heavier than uranium turned out to be greater than the abundance of carbon.

You discover a binary star system in which one star is a 15 MSun main-sequence star and the other is a 10 MSun giant. How do we think that a star system such as this might have come to exist?

The giant must once have been the more massive star, but is now less massive because it transferred some of its mass to its companion.

Which event marks the beginning of a supernova?

The sudden collapse of an iron core into a compact ball of neutrons.

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

The two stars should be the same age, so we'd expect the subgiant to be more massive than the main-sequence star.

Based on the diagram, which of the following statements best describes the observed pattern of abundances for elements with an atomic number between 6 and 20?

There is a general trend of decreasing abundance with increasing atomic number, but elements with even atomic numbers tend to be more abundant than those with odd atomic numbers.

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?

They generate energy through both hydrogen fusion and helium fusion.

According to our modern understanding of the origin of elements, why are hydrogen and helium so much more abundant than any other elements?

They were produced in the big bang

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

a 10 solar mass star

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

a red giant

This Hubble Space Telescope photo shows a planetary nebula. What is the white dot in the center (indicated by the arrow)?

a white dwarf

The ultimate fate of our Sun is to _____.

become a white dwarf that will slowly cool with time

The opening graph in the video shows the measured relative abundances of elements in the galaxy. What is the 4th most abundant element?

carbon

The following figures show various stages during the life of a star with the same mass as the Sun. Rank the stages based on when they occur, from first to last.

contracting cloud of gas and dust, protostar, main sequence G-star, red giant, planetary nebula, white dwarf

Provided following are various stages during the life of a high-mass star. Rank the stages based on when they occur, from first to last.

contracting clouds of gas and dust, protostar, main sequence O star, red supergiant, supernova and neutron star

Which of the following observations would not be likely to provide information about the final, explosive stages of a star's life?

decades of continuous monitoring of red giants in a globular cluster

Notice that nitrogen is less abundant than either carbon or oxygen. This is an example of the more general observation that __________.

elements with even atomic numbers are more abundant than the elements with odd atomic numbers that come between them

low mass stars

end life as a planetary nebula the sun is an example have longer lifetimes final corpse is a white dwarf

In this diagram, red balls represent protons and gray balls represent neutrons. What reaction is being shown?

fusion of helium into carbon

As the video shows, the star begins its life from a clump of gas that heats up as it contracts. Where does the energy that heats the cloud come from?

gravitational potential energy that the cloud loses as it shrinks in size

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

helium and helium

Provided following are various elements that can be produced during fusion in the core of a high mass main sequence star. Rank these elements based on when they are produced, from first to last.

helium, carbon, oxygen, iron

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

hydrogen fusion in a shell surrounding the central core

According to the diagram, what is the most abundant element with an atomic number greater than or equal to 20?

iron

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

its mass

our sun is considered to be a

low mass star

At which of the first five labeled stages is the star in energy balance?

main sequence and the next closest to main sequence

A main-sequence star twice as massive as the Sun would last __________.

much less than half as long as the Sun

Is a protostar in energy balance? Why or why not?

no, b/c its core generate less energy that its surface radiate into space

Suppose that hydrogen, rather than iron, had the lowest mass per nuclear particle. Which of the following would be true?

nuclear fusion could not power stars

The diagram indicates that the third most abundant element in the Milky Way Galaxy is _____.

oxygen

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

protostar, main sequence star, red giant, planetary nebula, white dwarf

A spinning neutron star has been observed at the center of a ______.

supernova remnant

high mass stars

te in life fuse carbon into heavier elements end life as a supernova have heavier fusion rate during main sequence life

Overall, careful study of the patterns revealed in the graph of measured element abundances has allowed scientists to __________.

test and validate models of how elements are produced by stars

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

the core shrinks while the rest of the star expands

Carbon fusion occur in high-mass stars but not in low-mass stars because _________.

the cores of low-mass stars never get hot enough for carbon fusion

What event brings the forming star into energy balance?

the onset of nuclear fusion in the core

The main illustration in the video shows the life track of a one-solar mass star. Each point along this track represents __________.

the star's surface temperature and luminosity at one time in its life

The fundamental lesson that we learn from the life track is that the star's outward appearance at any moment in its life reflects __________.

the way it is generating in its core