Stars and Galaxies- Final Exam
Which of the following statements about a Type II Supernova is TRUE?
A Type II supernova occurs at the end of the life of a star with ten times the mass of our Sun or more
The first satellite (spacecraft with instruments) to measure and confirm the cosmic microwave background was the:
COBE (COsmic Background Explorer)
Why did Einstein introduce the cosmological constant into the equations of his General Theory of Relativity when describing the universe?
Einstein's equations seemed to require the universe would unstably collapse under its own gravity; he assumed that the universe was static, so he put a factor in to stop it from moving
Who was the astronomer who is the "H" in H-R diagram?
Hertzsprung
The first astronomer that did photometry in a systematic way (even though he did not have a telescope) for whom we have written evidence was
Hipparchus
Which law do astronomers use to determine the masses of the stars in a spectroscopic binary system?
Kepler's Third Law
After a lot of work, a group of graduate students has finally measured the wavelengths of many dozens of lines in the spectrum of a distant star. If a number of the lines come from molecules such as titanium oxide, the star is likely to be which spectral type:
M
An eccentric Hollywood movie producer, vacationing in Australia, goes to an observatory and offers to make a big donation if they can show him a place in the Milky Way Galaxy where there are more than a million stars seen together. Which object would satisfy his extravagant tastes?
The globular cluster Omega Centauri
The standard bulbs (standard candles) that made it possible for astronomers to discover the acceleration in the expansion of the universe were
Type Ia supernovae
The rich galaxy cluster that is closest to our Local Group of galaxies is the
Virgo Cluster
Although centuries ago, astronomers thought that a nova was a new star, appearing for the first time in the heavens, today we know that it is:
a binary star system in which one star is a white dwarf and mass is being transferred to it
Objects orbiting around the center of the Milky Way obey Kepler's 3rd Law. This means that:
a cloud of gas or star that is further from the center will generally take more time to orbit
A type of star cluster that contains mostly very old stars is
a globular star cluster
A rich donor to your college gets fascinated by gamma-ray bursts, and wants to give money to find out more about what produces them. Which of the following should her money go to fund?
a network of visible-light telescopes which can automatically swing to a location provided by an alert system at NASA
The first, indirect detection of gravitational waves in the 1970s involved
a pulsar that was in the same star system with a neutron star
If you want to check on what conditions were like in the universe a few hundred thousand years after the Big Bang, what sort of instrument would it be best to use:
a satellite with infrared and microwave telescopes on board
Which of the following looks the brightest in the sky?
a star with a magnitude -1
Which of the following can a black hole not "eat" (absorb)?
actually, black holes can "eat" anything
In the very distant future, given our best model of the accelerating universe, what will the universe look like?
all the stars will die and the galaxies will be dark
Where is it certain to find the stars with the lowest mass on any H-R diagram?
among the stars at the bottom right of the main sequence
Which of the following statements about spectroscopic binary stars is FALSE?
an analysis of the ways the lines in the spectrum change allows us to calculate the star's distance directly
Suppose each of the following objects could collapse into a black hole. Each black hole would have a sphere around it that is the limit for escape -- once you are inside this region, you cannot get away. For which object would this region be the largest in diameter?
an entire galaxy of stars (with about a billion stars in it)
Compared to the mass of our own Milky Way Galaxy, the total mass we estimate for the Andromeda Galaxy is
approximately the same
By examining rich clusters of galaxies, such as the Coma Cluster, astronomers have discovered that spiral galaxies
are found mostly in the outer regions of such clusters, not in the middle
According to the models of the universe discussed in this course, why do the galaxies move apart (why do we have Hubble's law)?
as a result of the Big Bang, space itself is stretching, and this stretching carries the galaxies away from each other
Which of the following statements about dark matter is FALSE:
astronomers have a pretty good idea what the dark matter is made of
Which of the following statements about the early universe (as outlines in the standard model of cosmology) is FALSE?
at the very beginning, the energies were so great that the universe was actually contracting for a while
In the model that astronomers have developed for pulsars, why do they suggest that there must be two beams of energy coming from the pulsar?
because neutron star beams come out of the north and south poles of a magnetic field
Imagine that a brilliant but quirky scientist in the biology department manages to put you in a deep freeze and you wake up in a million years. Which of the following statements about the sky you would see in that future time is correct?
because of proper motion, a number of the familiar constellations will look somewhat different in a million years
Some "superstars" give off more than 50,000 times the energy of the Sun. Why are there no such stars among the stars that are close to the Sun?
because such very luminous stars are extremely rare, and thus any small neighborhood in the Galaxy is unlikely to contain one of them
Astronomers observe the Small Magellanic Cloud (SMC), a not very dense, rather small galaxy near us. They notice that even those stars that formed recently have relatively few heavier elements (when compared to such recent stars in our Milky Way.) What is the likely explanation for this deficiency?
because the SMC is small and its stars are widely spaced, the rate of star formation (and star death) is much slower there
Why can a star with a mass like our Sun not fuse (produce) further elements beyond carbon and oxygen?
because they just cannot get hot enough for the fusion of heavier nuclei
Because white dwarfs are small, as their name implies, they are hard to see. What is a way astronomers have to find white dwarfs that distinguishes them from main sequence stars?
because white dwarfs get really hot, we can search for their ultraviolet radiation
According to the most recent data from satellites making precise measurements of the properties of the cosmic microwave background (CMB),
dark energy makes up just a little less than 70% of the density of the universe, making it the most significant constituent of the mass-energy
Which of the following was NOT done by Edwin Hubble?
discovering the relationship between period and luminosity of a cepheid variable
Where in space did the expansion of the universe begin?
everywhere at once
When one member of a binary star system is a black hole, and astronomers detect flickering x-rays coming from the system, where are these x-rays usually coming from?
from a disk of material around the black hole (material that has been pulled from the companion star and is falling toward the black hole)
As a star becomes a giant, its outer layers are expanding. Where does the energy for expanding these layers come from?
from the fusion of hydrogen into helium in a shell around the core
Astronomers identify the main sequence on the H-R diagram with what activity in the course of a star's life?
fusing hydrogen into helium in their cores
Which is one reason that the typical galaxy's mass-to-light ratio (in units of the Sun's mass over the Sun's luminosity) generally greater than 1?
galaxies contain many more stars that shine much less brightly than the Sun
A handsome, rich, but vain movie star notices that he is starting to age, and consults you as his astronomy expert, to see if you can find an astronomical way to slow down his aging. Putting aside practical considerations (such as the fact that we cannot travel to other stars), which of the following strategies would IN THEORY allow him to age more slowly than the rest of humanity.
he should travel to a black hole, and spend some time in orbit just above the event horizon
In a distant galaxy, whose light is just arriving from 10 billion light years away, our spectroscope should reveal that the most common element is
hydrogen
If we want to see what galaxies looked like at a time close to the beginning of the universe, where should we look?
in a direction away from the plane of the Milky Way, where we can see very faint galaxies that are more than 10 billion light years away
If I want to find a sizeable collection of Population II stars in the Milky Way Galaxy, where would be a good place to look?
in a globular cluster high above the Galaxy's disk
If hydrogen is the most common element in the universe, why do we not see the lines of hydrogen in the spectra of the hottest stars?
in the hottest stars, hydrogen atoms are ionized, and so there are no electrons to produce lines in the spectrum
Which of the following statements about the Crab Nebula is FALSE?
inside, there are a number of newly formed massive stars (O and B type stars)
The most stable (tightly bound) atomic nucleus in the universe is:
iron
The cosmological principle in astronomy
is confirmed by many observations done by Hubble and many other astronomers since
Which of the following is NOT true about the Local Group of galaxies (of which the Milky Way is a member)?
it has more large elliptical galaxy members than spiral galaxies
If you trace back the history of a carbon atom in your little finger through all of cosmic history, where did this atom most likely originate?
it was fused from three helium nuclei in the core of a red giant star long before the Sun existed
What was especially noteworthy about the Sagittarius Dwarf Galaxy when it was discovered among the small galaxies near the Milky Way?
it was on a collision course with the Milky Way and would be swallowed by it eventually
Based on many surveys of the average density of matter in the universe (regular matter and dark matter), astronomers now conclude that the average matter density of the universe is
less than the critical density
An astronomer needs to measure the distance to a globular cluster of stars that is part of the Milky Way Galaxy. What method should she try to use to find the distance?
measure the flux of a variable star (cepheid or RR Lyrae) in the cluster to compare to its luminosity
Radio astronomy has played a pivotal role in showing us the detailed structure of the Milky Way Galaxy. Which of the following techniques would a radio astronomer use as an essential part of an investigation of this structure?
measuring the Doppler shift of a line in a radio spectrum
Wearing a very accurate watch, you volunteer to go on a mission to a black hole in a spaceship that has powerful rockets. You are able to orbit the black hole and stay a little distance outside of the event horizon. Compared to watches on Earth, your watch near the black hole will run:
more slowly
After it experiences a "helium flash" a star like the Sun will have a brief period of stability, fusing helium into carbon (and sometimes oxygen). During this brief stable stage, the star
none of the above
A graduate student in astronomy needs to measure the mass of a spiral galaxy she is studying for her PhD thesis. Which of the following observations would be important for her to make?
obtain the speed at which stars or gas near the outer regions of the galaxy are moving around
Astronomers call the motion of a star across the sky (perpendicular to our line of sight) its
proper motion
Far away from a black hole (at the distance of another star), which of the following is a possible way to detect it?
search for flickering x-rays being given off from an accretion disk around the black hole, as it "eats" part of a neighbor star
When do astronomers now think that the "dark energy" began to accelerate the expansion of the universe?
several billion years after the Big Bang
A graduate student has done a careful analysis of the spectrum of a star. While she has found lines from many elements, there was not a trace of the element helium in the spectra she has been analyzing. From this she can now conclude:
since helium shows lines only in hot stars, this star must be relatively cool
Our Milky Way Galaxy is what type of galaxy?
spiral
If you wanted to discover the youngest stars you could find in some grouping of stars in the Galaxy, which type of star group would be the best to search?
stellar associations
Which of the following is pretty good evidence that the universe began with a Big Bang?
the 3-degree cosmic microwave background radiation
The reciprocal of the Hubble constant (1/H) is a rough measure of the:
the age of the universe
Scientists speculate that the properties (laws) of the universe must be the way they are because if they were significantly different, we would not be here to think about them. This idea is called
the anthropic principle
Astronomers believe that the center of our Galaxy has a black hole with enough mass inside to make almost 4 million Suns! How do astronomers think a black hole could acquire so much mass?
the center of our Galaxy is a much more crowded region than where the Sun is found; we still see material falling toward the center and material has fallen in for billions of years
Astronomers believe that the many supernova explosions that happened in the Milky Way Galaxy could have played a role in the evolution of life over billions of years. How would they have influenced the development of life on Earth?
the cosmic rays produced by supernova explosions would have contributed to the rate of mutations over many generations
The boundary that surrounds the region around a black hole where everything is trapped, and nothing can get out to interact with the rest of the universe, is called
the event horizon
An astronomer is observing a distant galaxy which looks blue. Which of the following can she conclude from this observation?
the galaxy must have a lot of star formation going on at the time we are seeing it
If a very distant galaxy looks blue overall to astronomers, from this they can conclude that:
the galaxy must have a lot of young stars and thus active star formation must still be going in it
The model of the universe that involves an enormous increase of scale during a very short time in the early universe is called:
the inflationary universe model
How did Supernova 1987A demonstrate that new elements are made in supernova explosions?
the light output was kept at high levels by the energy released from radioactive elements that decay very quickly; these must have been made by the supernova
Recent observations indicate that the universe is expanding faster today than it was a few billion years ago (that, in other words, the expansion of the universe is accelerating.) What kind of observations have led astronomers to this surprising conclusion?
the measurement of galaxy distances using Type Ia supernovae
In the first direct detection of gravitational waves by LIGO in 2015, the waves came from
the merger of two black holes
In the far future, a starship becomes trapped inside the event horizon of a black hole. Although the crew discovers that their ship cannot out, they at least want to send a message to other ships in the area to stay away from the danger zone. If they send out a message in the form of a radio wave, what will be its fate?
the message will never emerge from the event horizon
Some scientists speculate that our universe is not the only universe that exists, but the only one we can gather evidence about. This idea is called
the multiverse theory
Which of the following is NOT a result of supernova explosions?
the neutron star is disrupted and tears apart into many fragments
A neutron star is as dense as
the nucleus of an atom
On an H-R diagram of a cluster of stars, which characteristic of the diagram do astronomers use as a good indicator of the cluster's age?
the point on the main sequence where stars begin to "turn off" -- to move toward the red giant region
Many names used by astronomers are misleading or outdated. A good example is the term planetary nebula, which astronomers use to refer to:
the shell let go by a dying low-mass star
In which of the following domains of the universe have astronomers NOT found evidence for the presence of dark matter today?
the solar system
The first time that astronomers observed both gravitational waves and electro-magnetic waves from the same event, what they were observing was:
the spiraling toward each other and eventual collision of two neutron stars
When a star undergoes a nova explosion, it may return to its "quiet state" and later become a nova again. What would allow a nova explosion to happen to a star more than once?
the star that goes nova has a companion star near it, which dumps material onto the first star and continues to do so even after the first nova explosion
What is the strongest known force in the universe at the scales of atomic nuclei and smaller?
the strong nuclear force
A "galactic year" as defined by astronomers is:
the time it takes the Sun to revolve once around the center of the Milky Way Galaxy
In a Type Ia supernova, the cause of the violent outburst is:
the transfer of so much mass from a companion star that a white dwarf goes "over the limit" and collapses, causing an enormous explosion
Edwin Hubble developed a classification scheme for galaxies. By what characteristic did he classify galaxies?
their shape
Recently, astronomers have observed stars and other objects that orbit the center of the Milky Way Galaxy farther out than our Sun, but move around faster than we do. How do astronomers think such an observation can be explained?
there must be a great deal of invisible dark matter outside the orbit of the Sun whose gravitational pull explains the faster motions we see out there
Astronomers now have a good idea for explaining how the short-duration gamma-ray bursts might come about. Which of the following is part of their explanation?
these bursts most likely come from the merger of two neutron stars
Among irregular galaxies, what makes the Large and Small Magellanic Cloud especially useful for astronomers?
they are (for galaxies) very close to us, so they are easy to study
How do astronomers measure the mass that the Galaxy contains inside the orbit of the Sun?
they measure the distance to the center of the Galaxy and the period of the Sun's orbit and then use Kepler's Third Law
Your sweetheart gives you a piece of gold jewelry as a present to celebrate your passing your astronomy class. Where did the gold atoms in that gift originally come from (where were they most likely made)?
they were built up from smaller nuclei during a collision of neutron stars
One important way astronomers can learn in some detail about what happens when galaxies collide is
to simulate galaxy collisions on a large computer and watch what the simulation predicts
Which of the following objects is considered useful to astronomers as a "standard bulb" for determining distances?
type Ia supernovae
What have we learned from the work of Harlow Shapley and others about the location of the Sun in the Milky Way Galaxy?
we are in the disk of the Galaxy, about 3/5 of the way from the center
When neutron stars were first predicted theoretically, no scientist expected to be able to detect one of them across interstellar distances. What enabled astronomers to find neutron stars in the late 1960s?
we found strongly magnetic neutron stars whose whirling beams of energy were detected as pulsars
When a single star with a mass equal to the Sun dies, it will become a
white dwarf
Which of the following can astronomers NOT learn from studying the spectrum of a star?
you can't fool me, all of the above can be learned from studying the spectrum
Before you can use Hubble's Law to get the distance to a galaxy, what observation must you make of that galaxy?
you must take a spectrum of the galaxy and measure the red shift
