Astronomy Test 4
Which of the following happens when two galaxies collide
- The shape of the galaxy is often changed - Large interstellar gas clouds collide - The rate of star formation increases - A smaller galaxy may wind up inside of a larger one
Which of the following is true about the Local Group of galaxies?
- it has more elliptical galaxy members than spiral galaxies - it has few galaxies when compared to a rich cluster - it is a member of the same supercluster as the Virgo Cluster - the Milky Way is one of its more massive members
Which of the followig can we learn from studying the Doppler shifts in the spectrum of galaxies beyond our Local Group?
- their red shifts - their distances - their rotation speeds - their masses (cannot learn whether they have Jupiter-size planets around many of their stars)
Which of the following happened during the first few minutes after the Big Bang?
- two or three of the simplest elements fused together - matter and antimatter collided and turned into energy - energy was converted to matter - temperatures throughout the universe were hotter than the cores of stars today
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
According to the models of the universe we discussed in this course, why do galaxies move apart?
As a result of the Big Bang, space itself is stretching, and this stretching carries the galaxies away from each other
Some astronomers searching for what the mysterious "dark matter" might be made of have pinned their hopes on MACHO's. What do you think these MACHO's are?
Black holes, brown dwarfs, and white dwarfs in the regions outside the main disk of our galaxy
Why did Einstein introduce the cosmological constant into the equations of his General Theory of Relativity when describing the universe?
Einstein's equations required the universe to expand or contract; he could no imagine or accept it doing either one, so he put a factor in it to stop it from moving
How do astronomers measure the mass that the Galaxy contains inside the orbit of the Sun?
the measure the distance to the center of the Galaxy and the period of the Sun's orbit and then use Kepler's Third Law
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
When astronomers say that the groups of galaxies are distributed isotropically, they mean that
the way galaxies are arranged in space looks the same in all directions
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 redshift
When we determine the age of the universe using the Hubble Time, what important simplifying assumption goes into our calculations?
That the expansion of the universe has been happening at the same rate - neither seeding up or slowing down
How do astronomers know that there aren't significant amounts of dark matter within our solar system?
a lot of dark matter would affect the motions (orbits) of our spacecraft as thy move through the solar system, and see no such effect
Astronomers making observations in our Galaxy have been able to rule out a number of suggestions for what the dark matter in the Galaxy might be. Which of the following have we NOT been able to rule out (which suggestion is still "in the running")?
a new kind of subatomic particle
The central region of our Galaxy is not as flat as its main disk of stars. Which of the following has roughly the same shape as our central region of stars?
a peanut
You suddenly get an uncontrollable urge to find out more about the other side of the Milky Way Galaxy (the regions beyond the center). Where should you rush off to?
a radio telescope that can observe at 21-cm wavelengths
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
The reciprocal of the Hubble constant (1/H) is a rough measure of the:
age of the universe
Astronomers not know that surrounding the main body of our Galaxy (which our various kinds of telescopes have shown to us) and our fainter halo of stars there is
an invisible halo made of what astronomers are calling "dark matter"
By examining rich clusters of galaxies, such as the Coma Clusters, astronomers have discovered that spiral galaxies
are found mostly in the outer regions of such clusters, not in the middle
When astronomers have examined rich clusters of galaxies with their instruments, they have found that these clusters
are more likely to contain giant elliptical galaxies than poor clusters
What method would astronomers use to find the distance to a galaxy so far away that individual stars are impossible to make out (resolve)?
finding the redshift and using Hubble's Law
In our modern view of the expansion of the universe, we understand that it is space that is stretching; individual galaxies don't speed away from each other as if they were rockets. In that case, why do galaxies show a red-shift?
as space stretches, the waves of radiation in space also stretch and their wavelength increases
Astronomers believe that the large elliptical galaxies formed
from the collision and merger of many smaller fragments
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 stars that shine much less brightly than the Sun
What do the surveys of the 3-D distribution of groups of galaxies reveal about how groups and clusters of galaxies are organized?
galaxy groups are organized into huge filaments with great voids between them -- something like the structure one would see taking a cross-section of some soap bubbles
Which of the following is the Earth not located in?
globular cluster M-13
What objects did Harlow Shapley use as "signposts" to figure out the extent of the Milky Way Galaxy and the location of its center
globular clusters
To map out how clusters of galaxies are distributed in the universe, astronomers needed to know where each cluster was in the sky AND
how far away from us each cluster was
Which of the following is a way that having an active galactic nucleus (AGN), with a supermassive black hole in the center, can affect the development of a galaxy
huge energetic jets from the accretion disk can disturb and lessen star formation in the galaxy
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
Which of the following statements about the implications of Hubble's Law is FALSE?
if you were observing the universe from a distant galaxy, you would NOT see all the galaxies (except those in your own group) moving away from YOU
Today, we believe that only a small number of elements were actually formed during the Big Bang. Which of the following was NOT one of these:
carbon
Which of the following statements about the different types (shapes) of galaxies is correct?
collisions and mergers between galaxies can sometimes charge a galaxy's type (shape)
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 a galaxy contains a great deal of "dark matter", what will that do the galaxy's mass-to-light radio?
increase it quite a bit
The cosmological principle in astronomy
is confirmed by many observations done by Hubble and many other astronomers since
According to the Cosmological Principle, the universe
is isotropic and homogeneous
Which of the following is not true about the Local Group of galaxies?
it has about a thousand member galacies
The Tully-Fisher method for measuring the distance to galaxies relies on the observed relationship between the luminosity of a spiral galaxy and
its rotational velocity (as determined from the width of the 21-cm line)
According to our modern "bottom-u" model of the formation of large structures in the universe, the strictures that formed first were about the mass of a
large globular cluster or a small galaxy
If we include the effects of deceleration in our calculation of the age of the universe, the age we get is:
less than the Hubble time
Based on many surveys of the average density of matter in the universe (regular matter and dark matter), astronomers now conclude that the average density of the universe is
less than the critical density
There is some irony in the fact that the Hubble Space Telescope has shown that Edwin Hubble's classification scheme for galaxy shapes only works in the later stages of the universe. What have really deep pictures (going way back in time) taken with the Hubble Telescope shown about galaxies long ago (in the first few billion years after the Big Bang)?
long ago, galaxy shapes were not (for the most part) regular and organized; galaxies looked chaotic and lumpy
In describing the universe using his equations of general relativity, Einstein assumed that it was isotropic (the same in all directions.) What recent observations have confirmed that the universe is isotropic on the large scale?
measurements of the 3-degree cosmic background radiation
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 a essential part of an investigation of this structure?
measuring the Doppler shift of a line in a radio spectrum
If a galaxy contains a great deal of dark matter, then, compared to the mass-to-light ratio of the inner part, the mass-to-light ratio of the whole galaxy will be
more
According to Hubble's Law, if two galaxies are not part of our Local Group, and galaxy B is three times farther away from us as Galaxy A, then Galaxy B will
move away from us three times faster than A
At about 1 seconf after the beginning of the universe, one type of particle was able to start traveling freely through the universe. These particles are still with us, but they are extremely hard to detect. They are called:
neutrinos
Which of the following is NOT a way astronomers can find how much dark matter there is in cluster of galaxies?
observe the radio waves coming from all dark matter; from the strength of the radio waves from each cluster, estimate the amount of dark matter needed to produce them
If you wanted to write a complete "cosmic address" for yourself, including every location or structure you live in, which of the following would be a part of that address?
planet Earth, the Solar System, the Milky Way Galaxy, the Local Group
When do astronomers now think that the "dark energy" began to accelerate the expansion of the universe?
several billion years after the Big Bang
Which of the following did NOT happen during the first few minutes after the Big Bang?
some very massive early stars formed
Compared to the mass of out own Milky Way Galaxy, the total mass we estimate for the Andromeda Galaxy is
somewhat bigger
Our Milky Way Galaxy is what type of galaxy?
spiral
The type of galaxy that sometimes has a distinct bar of stars running across the central regions is
spiral
The Tully-Fisher relation (looking at rotation speeds) only works for:
spiral galaxies
Why do galaxies collide, while stars almost never do?
stars are much further apart (compared to how big they are) than galaxies are
The Sloan Digital Sky Survey
takes images and spectra of millions of objects, to find the positions and redshifts of as many galaxies and quasars as possible
The new instrument that made it possible for Edwin Hubble to demonstrate the existence of other galaxies in the early 1920's was:
the 100-inch reflector on Mount Wilson
Which of the following is pretty goof evidence that the universe began with a Big Bang
the 3-degree cosmic microwave background radiation
How fo astronomers currently think the amount of detectable matter in the universe compares to the amount of dark matter and energy?
the amount of detectable matter is far less that the amount of dark matter and energy
Which of the following statements about our modern ideas of how spiral galaxies form and develop is TRUE?
the central bulges of spiral galaxies formed first and their disks formed later
According to the most recent data from satellites making precise measurements of the properties of the cosmic background radiation (CBR),
the 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
After the Big Bang, in order for the universe to become transparent to light and other electro-magnetic radiation, what had to happen?
the density of the universe had to decrease
William Herschel thought that the Sun and Earth were roughly at the center of the great grouping of stars we call the Milky Way. Today we know this is not the case. What was a key reason that Herschel did not realize our true position in the Milky Way?
the dust that extends throughout the disk of the Galaxy only allowed Herschel to see the small part of the Milky Way that surrounds us
Today, we believe that only a small number of elements were actually formed during the Big Bang. Which of the following were formed:
- hydrogen - helium - lithium
Factoring in everything we currently know about the history of the universe, our best estimate for the age of the universe is
13.8 billion years
According to our textbook, roughly what percent of the mass and energy of the universe is made up of dark matter plus dark energy?
95%
About two thirds of the nearby spiral galaxies (which we can study in more detail) don't have a round central bulge, but instead show
A central bulge with a bar of stars in the middle
Roughly how many galaxies make up our Local Group
About 60
The first satellite to measure and confirm the cosmic microwave background was the:
COBE
Which of the following does NOT happen when two galaxies collide
many of the stars collide
Which of the following statements about the nuclear bulge of our Galaxy is FALSE?
the best way to learn more about it is to observe higher energy radiation, such as ultraviolet and x-rays
Astronomers have measured that there is more helium in the universe than can be explained by the fusion in stars over the last 13 billion years. How do you think the extra helium go into the universe?
the extra helium was made during the first few minutes of the Big Bang, when the entire universe was hot enough for fusion to occur briefly
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
With enormous effort, a team of astronomers manages to collect enough light from a galaxy far, far away to produce a spectrum. That spectrum has lines from the elements carbon, silicon, and sulfer. This tells the team that
the galaxy must have had an entire generation of stars that was born, lived, and died
An astronomer discovers a massive galaxy which has four nuclei. What is a likely explanation for a galaxy having more than one nucleus?
the galaxy must have swallowed several smaller galaxies that were its neighbors
According to our modern theories, the geometry of the entire universe may be curved or warped. This is a pretty bizarre notion; what other discovery has helped us believe that space may be able to warp or curve?
the properties of black holes
In which of the following domains of the universe have astronomers NOT found evidence for the presence of dark matter today?
the solar systme
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
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
The reason type Ia supernovae are useful to astronomers for determining distances to other galaxies is that
they are very bright, and generally reach the same peak luminosity
Astronomers can now report that active star formation was going on at a time when the universe was only 20% as old as it is today. When astronomers make such a statement, how can they know what was happening inside galaxies way back when?
they examine the spectra of galaxies (or the overall colors of galaxies) with the highest redshifts they can find
The Andromeda Galaxy (our nearest spiral neighborhood) has spectral lines that show a blue shift. From this we may conclude that:
this particular nearby galaxy, is moving toward us
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
The standard bulbs (standard candles) that made it possible for astronomers to discover the acceleration in the expansion of the universe were
type Ia supernova
Which of the following objects is considered useful to astronomers as a "standard bulb" for determining distances?
type Ia supernovae
The "great voids" that astronomers studying galaxies are finding are:
very large regions of intergalactic space, where relatively few galaxies or galaxy clusters can be found
The two scientists who first discovered the cosmic microwave background radiation were:
Penzias and Wilson
The satellite that has given us the most precise measurements of the characteristics of the cosmic background radiation is
Planck
The scientist who made the first telescopic survey of the Milky Way and discovered that it is composed of a huge number of individual stars was
Galileo Galilei
The first scientist to propose a specific model (the primeval atom model) for the Big Bang was
Lemaitre
The astronomer who assisted Edwin Hubble at the Mount Wilson Observatory and helped him establish the expansion of the universe was:
Milton Humason
Why us the use of Hubble's Law to measure distances to galaxies so important to astronomers?
Most galaxies are so far away, the only way to get distances to them is to use Hubble's Law
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
Your weird cousin, who is really into astronomy, decides that the return address he uses on his letters is incomplete! To his city, state, and country, he begins to add: "North America, Earth, Solar System..." If he now wants to include the name of the Galaxy's spiral-structure feature in which the Earth is located, how should his address end?
Orion Spur
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
The first astronomer to show that spiral nebulae (today called spiral galaxies) have large Doppler shifts was
Vesto Slipher
The rich galaxy cluster that is closest to out Local Group of galaxies is the
Virgo Cluster
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
At first, right after the Big Bang, the universe was too hot for nuclei and electrons to combine into the kinds of neutral atoms that are familiar to us today. How soon after the beginning did it become cool enough for neutral atoms to form
a few hundred thousand years
Which of the following is NOT a characteristic of a spiral galaxy?
When we take spectra of its stars, they have far less of the heavier elements than the Sun
Which of the following statements about dark matter in the Galaxy is FALSE?
While the dark matter cannot be observed with our present-day instruments, we still have a pretty good idea what it consists of
Astronomers today know a lot about the size and shape of the Milky Way Galaxy. Which of the following common objects most resembles the shape of our Galaxy?
a CD or DVD
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
Galaxies that we see as they were 11 billion years ago or more, as compared to galaxies today, are generally:
bluer and smaller
One of the most important observations in the history of astronomy was the one by Edwin Hubble that established that there other galaxies, quite removed from the Milky Way. How did Hubble show this?
by observing a Cepheid variable in a nearby galaxy and using it to get the distance
According to our current understanding, giant elliptical galaxies form:
by the merger (or swallowing) of a number of smaller galaxies in a cluster of galaxies
Which of the following was not done by Edwin Hubble?
discovering the relationship between period and luminosity of a cepheid variable
Which type of galaxy is very difficult to see, but (astronomers recently realized) may be very common?
dwarf elliptical
They type of galaxy that consists almost entirely of old stars and is thus less blue (more yellow and reddish) than the other types is:
elliptical
Which type of galaxy is observed to contain mostly older stars?
elliptical
Where in space did the expansion of the universe begin?
everywhere at once
Edwin Hubble was able to show that (with the exception of our nearest neighbors) the farther a galaxy is from us, the
faster it is moving away from us
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?
find a variable star (cepheid or RR Lyrae) in the cluster
One of the main projects being carried out by the Hubble Space telescope is to measure the distances of galaxies located in groups dozens of millions of lightyears away. What method do astronomers use with the Hubble to find such distances?
finding Cepheid variables and measuring their periods
