Astronomy 1 Midterm 3 Study Ch. 16-18

When does a newly forming star have the greatest luminosity?

when it is a shrinking protostar with no internal fusion

How do the properties of long-lived stars compare to those of short-lived stars? Check all that apply.

-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.

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.

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

1/1000 that of hydrogen

The life tracks shown on the diagram for different mass protostars are based on computer models. Observationally, how can astronomers test whether these models are correct?

By observing and comparing protostars and stars of different masses within a single star cluster.

The following figures show four stages that occur during the formation of a one-solar-mass star. Rank these stages based on their rotation rate, from fastest to slowest.

Fastest to slowest rotation: -main-sequence star -protostar with jets -contracting cloud trapping with infrared light -molecular-cloud fragment

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.

First to last produced: -helium -carbon -oxygen -iron

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.

First to last stage: -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.

First to last stage: -contracting cloud of gas and dust -protostar -main-sequence O star -red supergiant -supernova -neutron star

The following figures show four stages that occur during the formation of a one-solar-mass star. Rank these stages based on the order in which they occur, from first to last.

First to last to occur: -molecular-cloud fragment -contracting cloud trapping infrared light -protostar with jets -main-sequence star

Listed following are characteristics that describe either high-mass or low-mass stars. Match these characteristics to the appropriate category.

High-mass stars: -end life as a supernova -late in life fuse carbon into heavier elements -have higher fusion rate during main sequence life Low-mass stars: -final corpse is a white dwarf -the Sun is an example -have longer lifetimes -end life as a planetary nebula

Provided following are four different ranges of stellar masses. Rank the stellar mass ranges based on how many stars in each range you would expect to be born in a star cluster, from highest number to lowest number.

Highest to lowest number: -less than 1 solar mass -between 1 and 10 solar masses -between 10 and 30 solar masses -between 30 and 60 solar masses

Provided following are the spectral types of four different main-sequence stars. Rank the stars based on the strength of the radiation pressure that pushes outward as they are forming, from highest pressure to lowest pressure.

Highest to lowest radiation pressure: -O9 -A5 -G2 -M6

The following figures show four stages that occur during the formation of a one-solar-mass star. Rank these stages based on the central temperature, from highest to lowest.

Highest to lowest temp: -main-sequence star -protostar with jets -contracting cloud trapping infrared light -molecular-cloud fragment

Watch the red dot representing the protostar in the video. After it reaches its highest point on the diagram, how do the protostar's surface temperature and luminosity change as it approaches the main sequence?

Its surface temperature increases, but its luminosity decreases.

The following figures show the spectral types of four main-sequence stars. Rank them based on the time each takes, from longest to shortest, to go from a protostar to a main-sequence star during the formation process.

Longest to shortest time: -M6 -G2 -A5 -O9

Each item following is a characteristic of a one-solar-mass star either during its protostar phase or during its main-sequence phase. Match the items to the appropriate phase.

Protostar phase: -energy generated by gravitational contraction -radius much larger than the Sun -pressure and gravity are Not precisely balanced -luminosity much greater than the Sun Main-sequence phase: -energy generated by nuclear fusion -lasts about 10 billion years -surface radiated energy at same rate that core generates energy

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.

Suppose two protostars form at the same time, one with a mass of 0.5MSun and the other with a mass of 15MSun. Which of the following statements are true?

The 15MSun star will end its main-sequence life before the 0.5MSun star even completes its protostar stage.

Based on the protostar tracks on the diagram, which statement must be true about the Sun?

The Sun was much more luminous when it was a protostar than it is today.

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.

Assume that all four H-R diagrams below represent a star in different stages of its life, after it starts to fuse hydrogen in its core. Rank the HR diagrams based on when each stage occurs, from first to last.

The diagram at the left represents the Sun (or any other one-solar-mass star) as a hydrogen-burning main-sequence star, with spectral type G and one solar luminosity. The next diagram shows the Sun after it has exhausted its core hydrogen and left the main sequence, making it a subgiant with energy generated by hydrogen burning in a shell around an inert helium core. The third diagram shows the Sun a little later; its energy source is still hydrogen shell burning, but at this point it has expanded in size so much that it is a red giant. The final diagram (far right) shows the white dwarf corpse of a one-solar-mass star; it is hot because it is the exposed core of the dead star, but dim because it is small in size.

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.

When a newly forming star is at its greatest luminosity, what is its energy source?

gravitational contraction

As a clump of interstellar gas contracts to become a main-sequence star, its changing position on the H-R diagram tells us __________.

how its outward appearance is changing

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

in the Big Bang

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

iron

The five colored curves on the diagram have arrows pointing to the left. Each of these five curves represents a star of a different __________.

mass

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

much less than half as long as the Sun

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

oxygen

The arrows on each protostar's curve on the diagram's indicate that __________.

protostars change in surface temperature and luminosity as they develop

Which protostars maintain nearly the same luminosity throughout the time that they are protostars?

protostars with masses about 10 or more times that of the Sun