ASTR 101 Chapter 13
When the Sun is a red giant, what will its approximate surface temperature be?
3,500 K
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
What would you be most likely to find if you returned to the solar system in 10 billion years?
A white dwarf
What would stars be like if hydrogen had the smallest mass per nuclear particle?
Nuclear fusion would not occur in stars of any mass.
Listed following are characteristics that describe either high-mass or low-mass stars. Match these characteristics to the appropriate category.
HIGH-MASS STARS(>8 Msun) -end life as a supernova -late in life fuse carbon into heavier elements -have higher fusion rate during main sequence life LOW-MASS STARS(<2 Msun) -end life as a planetary nebula -final corpse is a white dwarf -have longer lifetimes -the Sun is an example
Why are red giant stars rare compared to main sequence stars?
The amount of time a red giant lasts is small compared to the lifespan of a main sequence star.
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
When the core of a star like the Sun uses up its supply of hydrogen for fusion, the core begins to _____________.
shrink and heat
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.
-less than 1 solar mass -between 1 and 10 solar masses -between 10 and 30 solar masses -between 30 and 60 solar masses
What will the Sun's approximate luminosity be during the subgiant stage?
10 Lsun
Which of these stars does not have fusion occurring in its core?
A red giant
Fusion of a carbon nucleus with another carbon nucleus.
^24 Mg(12p, 12n)
Fusion of a carbon nucleus with a neon nucleus.
^32 S(16p, 16n)
A brown dwarf is
an object not quite massive enough to be a star
At point B, the star is:
burning helium in its core and hydrogen in a shell.
Shown here is the track on the H-R diagram of a star like the Sun. At point A the star is:
burning hydrogen in a shell around a collapsing core.
According to current understanding, the two most abundant elements in the universe were made ____________.
in the Big Bang
Star-forming clouds appear dark in visible-light photos because the light of stars behind them is absorbed by _____________.
interstellar dust
When a star exhausts its core fusion fuel so that the core begins to contract, which of the following can stop the contraction? CHECK ALL THAT APPLY.
-Degeneracy pressure -Fusion of another element
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.
-M6 -G2 -A5 -O9
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.
-O9 -A5 -G2 -M6
Match words at the left to the correct blanks in the sentences on the right. Not all words will be used.
-The energy that drives the expansion of a star into a subgiant or red giant comes from HYDROGEN SHELL FUSION -Stars with mass greater than about 8 solar masses are considered HIGH-MASS STARS -The final stage of core fusion in a low-mass star is HELIUM FUSION -Stars that are fusing hydrogen in their cores are MAIN-SEQUENCE STARS -When it dies, a high-mass star explodes as a SUPERNOVA -A star that is expanding (into a subgiant and then a giant) has a(n) INERT HELIUM CORE -When it dies, a low-mass star expels a PLANETARY NEBULA -Stars with masses less than about two solar masses are considered LOW-MASS STARS
Match the words at the left to the correct blanks in the sentences at right.
-a forming star spins more rapidly as it collapses because of conservation of ANGULAR MOMENTUM -the collapse of a protostar with less than 0.08 times the mass of the Sun is halted by DEGENERACY PRESSURE -as a protostar shrinks in size, its central temperature rises along with its THERMAL PRESSURE -a star that has not yet finished forming is called a PROTOSTAR -if a protostar has a mass too small for it to sustain nuclear fusion, it becomes the type of object known as a BROWN DWARF -a star is born when it comes into ENERGY BALANCE, in which the energy released by fusion matches the energy it radiates into space -a gas cloud in which gravity is perfectly balanced against pressure is said to be in GRAVITATIONAL EQULIBRIUM
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
According to the diagram, the approximate abundance of oxygen atoms in the galaxy is ______________.
1/1,000 that of hydrogen
You observe a star cluster and find the hottest star in the cluster is 20,000 K (corresponding to a B-type star). The age of the cluster is
10 million years
When the Sun becomes a white dwarf with a surface temperature similar to its current surface temperature, what will its luminosity be?
10^-4 Lsun
Just before the Sun produces a planetary nebula, what will its approximate luminosity be?
10^4 Lsun
How much brighter in our sky than Sirius would the Betelgeuse supernova be if it reached a maximum luminosity of 9.0x10^9 Lsun? EXPRESS YOUR ANSWER USING TWO SIGNIFICANT FIGURES.
61921.88
The diagram indicates that the third most abundant element in the Milky Way Galaxy is _____________.
oxygen
According to the diagram, what is the most abundant element with an atomic number greater than or equal to 20?
Iron
In what way is iron unique among the elements?
It has the lowest mass per nuclear particle.
What happens to the core of a high-mass star after it runs out of hydrogen?
It shrinks and heats up.
What happens to low-mass star after helium flash?
Its luminosity goes down.
Each of the 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: -luminosity much greater than the Sun -radius much larger than the Sun -pressure and gravity are not precisely balanced -energy generated by gravitational contraction MAIN SEQUENCE PHASE: -energy generated by nuclear fusion -lasts about 10 billion years -surface radiates 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.
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.
In the dying stages of our Sun, it will fuse helium into carbon. After that what will occur?
The core contracts, but the carbon never fuses.
At left is a young star cluster. All the cluster stars formed at about the same time. if you were to observe this star cluster over several billion years, you would see:
many supernovae early on, and then no more.
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
I just discovered a 3.5 Msun main sequence star orbiting a 2.5 Msun red giant. I'll bet that red giant was more massive than 3 Msun when it was a main sequence star.
True. For that to be true, the red giant would have been more massive than the partner in the past, and that would be true if it began as more than 3.0 MSun.
Fusion of an iron nucleus with a helium nucleus.
^60 Ni(28p, 32n)
A supernova occurs when:
a massive star burns through successively heavier elements until it has an iron core, which will not release energy from fusion.
Why doesn't a high-mass star fuse its iron into heavier elements, like uranium?
no rest-mass energy is released due to fusion of iron.
Stars can form most easily in clouds that are
cold and dense
The basic requirement for a cloud to collapse to form a star is that _____________.
gravity must be strong enough to overpower the cloud's internal pressure
At point C, the star:
has a stable, inert carbon core and essentially no hydrogen or helium.
