In which of the following layer(s) of the Sun does nuclear fusion occur?
answer
core
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Which of the following layers of the Sun can be seen with some type of telescope? Consider all forms of light, but do not consider neutrinos or other particles
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chromosphere, photosphere, corona
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Hydrogen fusion in the Sun requires a temperature (in Kelvin) of
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millions of degrees
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Why are neutrinos so difficult to detect?
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because they rarely interact with matter
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Listed following are events or phenomena that occur during either the part of the sunspot cycle known as solar minimum or the part known as solar maximum. Match these items to the correct part of the sunspot cycle
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all are solar maximum except : occurs about 5 to 6 years after a solar maximum (on average)
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Why does the energy produced by fusion in the solar core take so long to reach the solar surface?
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Photons take hundreds of thousands of years to get out of the sun because their paths zigzag repeatedly. Because the plasma is so dense, photons can only travel a fraction of a millimeter before colliding with an electron and deflecting in a new direction
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If the distance between us and a star is doubled, with everything else remaining the same, the luminosity
answer
remains the same, but the apparent brightness is decreased by a factor of four.
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Suppose you measure the parallax angle for a particular star to be 0.1 arcsecond. The distance to this star is
answer
10 par sec
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Which of the following statements about apparent and absolute magnitudes is true?
A) The magnitude system that we use now is based on a system used by the ancient Greeks over 2,000 years ago that classified stars by how bright they appeared.
B) A star with apparent magnitude 1 is brighter than one with apparent magnitude 2.
C) The absolute magnitude of a star is another measure of its luminosity.
D) A star's absolute magnitude is the apparent magnitude it would have if it were at a distance of 10 parsecs from Earth.
E) All of the above are true.
answer
all of the above
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The spectral sequence in order of decreasing temperature is
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OBAFGKM
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If star A is closer to us than star B, then Star A's parallax angle is
answer
larger than that of Star B
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Why are Cepheid variables so important for measuring distances in astronomy?
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Their luminosity can be inferred from their period
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Astronomers can measure a star's mass in only certain cases. Which one of the following cases might allow astronomers to measure a star's mass?
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the star is a member of a binary star system
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The ____________________is greater for low-mass stars than it is for high-mass stars.
answer
main-sequence lifetime
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The stars known as________________________ are the very largest and brightest of all the stars
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supergiants
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Stars are classified on the basis of their spectral type and ___________________
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luminosity class
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Cepheids are examples of ________________________
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pulsating variable stars
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_____________________are no longer generating energy through nuclear fusion
answer
White dwarfs
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Stars that are cooler than the Sun yet 100 to 1,000 times as luminous as the Sun are classified as ______________
answer
giants
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Which of the following statements about an open cluster is true?
answer
all stars in a cluster are approx the same age
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Which of the following statements about a globular cluster is true?
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Most stars in the cluster are yellow or reddish in color.
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in order to understand star clusters, we need to be able to estimate their ages. What technique do scientists use for this
answer
finding the main-sequence turnoff point of the stars
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Astronomers estimate that new stars form in our galaxy at the rate of about
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a few (2-3) per year.
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The most abundant molecule in molecular clouds is
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H2
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What is interstellar reddening?
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Interstellar dust absorbs more blue light than red light, making stars appear redder than their true color
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If you wanted to observe stars behind a molecular cloud, in what wavelength of light would you most likely observe?
answer
infared
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When does a protostar become a true star?
answer
when nuclear fusion begins in the core
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Which star spends the longest time in the protostellar phase of life?
answer
a 1 solar mass star
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What effects are jets and magnetic fields thought to have on a protostar?
answer
What effects are jets and magnetic fields thought to have on a protostar?
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The arrows on each protostar's curve on the diagram's indicate that __________.
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protostars change in surface temperature and luminosity as they develop
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What is the smallest mass a newborn star can have?
answer
80 times the mass of Jupiter
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What is the greatest mass a newborn star can have
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a few hundred solar masses
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What do astronomers mean when they say that we are all "star stuff"?
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that the carbon, oxygen, and many elements essential to life were created by nucleosynthesis in stellar cores
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What type of star is our Sun?
answer
low-mass star
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Which of the following sequences correctly describes the stages of life for a low-mass star?
answer
protostar, main-sequence, red giant, white dwarf
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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)?
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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
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The star expels its outer layers into space almost immediately upon the end of Stage
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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.
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What element(s) should you expect to be most abundant in the star when it reaches Stage 6?
answer
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.)
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Which statement accurately describes the length of Stage 1 compared to Stages 2 through 5?
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Stage 1 lasts nearly 10 times as long as Stages 2 through 5 combined.
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At which of the first five labeled stages is the star in energy balance?
answer
The star is in energy balance when its core energy production matches the amount of energy it radiates into space. As explained in the video, this is true only when the star is a main-sequence star with hydrogen core fusion and when it is a helium core-fusion star. It is out of energy balance at all other times, which is why it is either contracting or expanding.
question
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.
answer
contracting cloud of gas and dust, protostar, main sequence G-star, red giant, planetary nebula, white dwarf
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What is the CNO cycle?
answer
a type of hydrogen fusion that uses carbon, nitrogen, and oxygen atoms as catalysts
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What types of stars end their lives with supernovae
answer
tars that are at least several times the mass of the Sun
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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
answer
- contracting cloud of gas and dust
- protostar
- main-sequence O star
- red supergiant
- supernova
- neutron star
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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.
answer
- helium
- carbon
- oxygen
- iron
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Betelgeuse is a supergiant star that will eventually supernova, which means that by mass it is classified as a ____
answer
high mass star
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The debris from the death of a high-mass star forms a ___ several light years across.
answer
supernova remnant
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A _____ has a density higher than the density of a white dwarf.
answer
neutron star
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____ actually occurred about 150,000 years ago in the Large Magellanic Cloud.
answer
supernova 1987a
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The ____ is the process by which hydrogen fusion proceeds in high-mass stars.
answer
CNO cycle
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Carbon can be converted into oxygen in the cores of high-mass stars if carbon nuclei undergo a _____ .
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helium capture reaction
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Which of these elements had to be made in a supernova explosion?
answer
uranium
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White dwarfs are so called because
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they are both very hot and very small
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Which of the following is closest in mass to a white dwarf?
answer
the Sun
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What is the ultimate fate of an isolated white dwarf?
answer
it will cool down and become a black dwarf
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Suppose a white dwarf is gaining mass because of accretion in a binary system. What happens if the mass someday reaches the 1.4-solar-mass limit?
answer
The white dwarf undergoes a catastrophic collapse, leading to a type of supernova that is somewhat different from that which occurs in a massive star but is comparable in energy.
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which of the following is closest in size to a white dwarf
answer
earth
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Observationally, how can we tell the difference between a white-dwarf supernova and a massive-star supernova?
answer
The spectrum of a massive-star supernova shows prominent hydrogen lines, while the spectrum of a white-dwarf supernova does not
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A(n) "accretion disk"
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consists of hot, swirling gas captured by a white dwarf (or neutron star or black hole) from a binary companion star.
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A(n) "nova"
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occurs when hydrogen fusion ignites on the surface of a white dwarf in a binary system.
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A(n) "massive star supernova"
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occurs when fusion creates iron in the core of a star.
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"white dwarf limit (1.4 solar masses)".
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A white dwarf in a close binary system will explode as a supernova if it gains enough mass to exceed the
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A(n) "white dwarf supernova"
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can occur only in a binary system, and all such events are thought to have the same luminosity.
question
electron degeneracy pressure
answer
The radius of a white dwarf is determined by a balance between the inward force of gravity and the outward push of
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After a massive-star supernova, what is left behind?
answer
either a black hole or a neutron star
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What causes the radio pulses of a pulsar?
answer
As the star spins, beams of radio radiation sweep through space. If one of the beams crosses Earth, we observe a pulse.
question
There is no upper limit to the mass of a neutron star
answer
false
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All pulsars are neutron stars, but not all neutron stars are pulsars.
answer
true
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How do we know what happens at the event horizon of a black hole?
answer
we dont know for sure : we only know what to expect based on the predictions of general relativity
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What makes us think that the star system Cygnus X-1 contains a black hole?
answer
What makes us think that the star system Cygnus X-1 contains a black hole?
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- has a mass no greater than 1.4M SUn
-typically about the size (diameter) of Earth
- in a binary system, it can explode as a supernova
-supported by electron degeneracy pressure
answer
white dwarf
question
- usually very strong magnetic field
- sometimes appears as a pulsar
answer
Neutron star
question
-viewed from afar, time stops at its even horizon
- size defined by its schwarzchild raduis
answer
blackhole
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What does Einstein's general theory of relativity tell us about two co-orbiting white dwarfs?
answer
they will emit gravitational waves that carry energy and angular momentum away from the system, causing the white dwarfs to gradually spiral inward toward each other and eventually merge
question
What powers the sun?
answer
nuclear fusion
question
what pushes out a star? what is trying to crush a star?
answer
between the outward push of internal gas pressure and the inward pull of gravity.
question
What is the energy balance of the sun?
answer
The rate at which energy radiates from the surface of the Sun must be the same as the rate at which it is released by fusion in the core.
where hot gas moves up toward the surface and cooler gas moves deeper into the interior
question
radiation zone
answer
A region of very tightly packed gas in the sun's interior where energy is transferred mainly in the form of light.
question
Solar Thermostat
answer
Decline in core temperature causes fusion rate to drop, so core contracts and heats up.
Rise in core temperature causes fusion rate to rise, so core expands and cools down
question
solar activity
answer
short-lived phenomena on the Sun, including the emergence and disappearance of individual sunspots, prominences, and flares; sometimes called solar weather
question
when is the sun most active?
answer
solar maximum, when sunspots are most are most numerous
question
when is the sun least active?
answer
solar minimum- least sunspots
question
what is the average length of time between solar maximums
answer
11 years
question
what causes solar activity
answer
All of these features are created by magnetic fields, which form and change easily in the convecting plasma in the outer layers of the Sun.
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how does the activity of the sun affect earth?
answer
research remains
question
what is brightness and luminosity?
answer
Luminosity is a measure of power, and apparent brightness is a measure of power per unit area.
question
inverse square law
answer
A physical quantity varies inversely as another quantity squared.
question
what is parallax?
answer
the apparent change in position of an object when you look at it from different places
question
how does parallax depend on distance?
answer
cause of the shift
question
Parsec (pc)
answer
The distance to an object with a parallax angle of 1 arcsecond; approximately equal to 3.26 light-years.
question
Parallax formula
answer
Distance in ly: 3.26ly/parallax angle in arcsec
Distance in pc: 1/parallax angle in arcsec
Only stars within 120pc have parallax angles great enough to calculate their distance
question
apparent magnitude
answer
the brightness of a star when viewed from Earth
question
absolute magnitude
answer
is the apparent magnitude it would have if it were at a distance of 10 parsecs (32.6 light-years) from Earth
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