Astronomy chapter 17
According to the diagram, the approximate abundance of oxygen atoms in the galaxy is __________.
1/1000 that of hydrogen
This photo shows the famous Crab Nebula. What is it?
An expanding cloud of remains from a star that died in a supernova.
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.
The opening graph in the video shows the measured relative abundances of elements in the galaxy. What is the 4th most abundant element?
Carbon
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.
According to this diagram, how much more abundant is hydrogen in the universe than nitrogen?
Hydrogen is about 10,000 times as abundant as nitrogen.
According to the diagram, what is the most abundant element with an atomic number greater than or equal to 20?
Iron
Which of the following describes a star with a hydrogen-fusing shell and an inert (nonfusing) helium core?
It is a subgiant that grows in luminosity until helium fusion begins in the central core.
Is a protostar in energy balance? Why or why not?
No, because its core generates less energy than its surface radiates into space.
The diagram indicates that the third most abundant element in the Milky Way Galaxy is _____.
Oxygen
Which is more common: a star blows up as a supernova, or a star ejects a planetary nebula?
Planetary nebulas are more comon
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 it is now less massive because it transferred some of its mass to its companion.
What event brings the forming star into energy balance?
The onset of nuclear fusion in the core.
Which event marks the beginning of a supernova?
The sudden collapse of an iron core into a compact ball of neutrons.
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.
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
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 cloud of gas and dust, protostar, main-sequence O star, red supergiant, supernova, neutron star
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.
contracting clouds of gas and dust, protostar, main-sequence G star, red giant, planetary nebula, white dwarf
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 (<2 Msun)
final corpse is a white dwarf have longer lifetimes ends in planetary nebula the sun is an example
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
Suppose a particular star has a core that is undergoing several stages of fusion simultaneously, as shown in this diagram. Based on our understanding of stellar lives, the mass of this star is probably ____________.
greater than 8 times the mass of the sun
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, carbon
According to current understanding, the two most abundant elements in the universe were made __________.
in the big bang
high mass stars
late in life fuse carbon into heavier elements have higher fusion rate during main sequence life ends life as supernova
Our Sun is considered to be a ______.
low-mass star
Suppose that hydrogen, rather than iron, had the lowest mass per nuclear particle. Which of the following would be true?
nuclear fusion could notpower stars
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
Carbon fusion occurs in high-mass stars but not in low-mass stars because _________.
the cores of low-mass stars never get hot enough for carbon fusion
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 energy in its core
