AST 115 Final Exam
Edwin Hubble established the existence of separate, distant galaxies when he found ______stars in the ______ Nebula and used them to measure its distance. He did this work with the worlds largest telescope (at the time) at the _________. Hubble classified galaxies on the basis of their shapes, into spirals, _____________, and irregulars. Later, working with his assistant, ___________, he built upon Vesto Slipher's observations from ___________ that most of the galaxies were moving away from us and found that the further away a galaxy was, the _______ it was moving away.
- Cepheid variable -Andromeda -Mt. Wilson observatory -ellipticals - Milton Humanson -spectra -faster
which of the following is NOT part of the growing chain of evidence that makes many astronomers suspect there is a black hole at the very center of the Milky Way galaxy?
the Hubble space telescope has shown us a visible-light image of an accretion disk at the center of the galaxy
which of the following objects is considered useful to astronomers as a " standard candle" for determining distances?
type la 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
the dark matter halo
we don't know what its made of
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
Since 1990 or so, astronomers have been able to observe galaxies much further away ( whose light comes from longer ago) than before. They have a clearer view of their shapes, because they had access to telescopes that are _______. Galaxies seen more than 8 billion light-years away, don't fit into the galaxy classification scheme that was put together by __________. Instead of galaxies seem systematically ________ than nearby galaxies. Because of collisions and mergers, we now know that galaxies have ________ as the universe has gotten older.
- in space -Hubble -clumpier -snmaller -grown in size
State the astronomical objects in order of size, from smallest to largest
-the event horizon of the black hole at the center of the Milky Way Galaxy -the solar system -globular cluster M13 -the Perseus spiral arm -the Milky Way galaxy
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
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
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
astronomers now think that there is a black hole with more than 4 million times the mass of our sun at the center of our galaxy? roughly how large would the even horizon of such a supermassive black hole be?
about 17 times the size of the sun
in the future, astronomers believe that the Milky Way galaxy has additional collisions in store. which of the following nearby galaxies are eventually going to collide with our own?
all of these
Astronomers now know that permeating 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"
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
which of the following statements about the different types (shapes) of galaxies is correct ?
collisions and mergers between galaxies can sometimes change a galaxy's type (shape)
the type of galaxy that consist 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
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 dozen of millions of light-year away. What method do astronomers use with Hubble to find such distances?
finding cepheid variables and measuring their periods
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
which of the following statement about the implications of Hubble 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
where would you look for the youngest stars in the Milky Way galaxy?
in the disk
if a galaxy contains a great deal of "dark matter", what will that do the galaxy's mass-to-light ratio?
increase it quite a bit
the thick disk
it contains just a few percent of the stars in the galaxy
the thin disk
it contains most of the stars in the galaxy
what was especially noteworthy about the sagittarius dwarf galaxy when it was discovered in 1994 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
the Tully-fisher method for measuring the distance to galaxies relies on the observes relationship between the luminosity of a spiral galaxy and
its rotational velocity (as determined from the width of the 21-cm line)
the stellar halo
its stars were born a long time ago (13 billion years)
why is 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
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 than Galaxy A, then galaxy B will
move away from us three times faster than A
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
the very strong source of radio waves at the center of our galaxy is called
sagittarius A
Compared to the mass of our 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
astronomers believe that the center of our galaxy has a black hole with enough mass inside to make about 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
William Herschel thought that the sun and Earth were roughly at the center of the great grouping of strs we call the Milk 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
which of the following is evidence that the formation process of our galaxy may have included collisions with smaller neighbor galaxies?
the observation of long moving streams of stars that continue to orbit through our galaxy's halo
what leads astronomers to conclude that the proto-glatic cloud (the cloud from which our galaxy formed ) was roughly spherical?
the oldest stars in the galaxy (population II stars, globular clusters) form a spherical halo around the galaxy; they outline the original shape of the cloud that gave the galaxy birth
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
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
the Andromeda galaxy (our nearest spiral neighbor) has spectral lines that show a blueshift. From this we may conclude that;
this particular nearby galaxy is moving toward us
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
one way astronomers have been able to figure out the structure of remote parts of our galaxy is by using the 21-cm radio line in the spectrum of the element _____. The galaxy turns out to have a number of _____, on which most of the stars and interstellar matter in the disk are located. The sun is located on a short and not especially impressive one of these, called the __________. Astronomers use the motion of stars together with ______ to help them measure the mass in various parts of the galaxy. Modern measurements have revealed that there must be a lot of mass on the outskirts of the galaxy, an yet we don't detect many stars or other familiar objects out there. Thus astronomers call this extra mass around the galaxy _____________.
- hydrogen -spiral arms -orion spur -kepler's third law -dark matter
the way Edwin Hubble showed that other galaxies exist was to measure a distance to a galaxy and show that it was greater than any estimates of the size of our own Milky Way. The first galaxy for which he measured a distance was M31, the galaxy in ________. He did that measurement using a class of stars called ___________, whose variations in luminosity could be used to estimate their distance. Astronomers continued that work, measuring those kinds of stars in other nearby galaxies with other telescopes. Such measurements have recently been done in even more distant galaxies using _____. Another way to measure distances is to find objects that behave like "standard bulbs;" one especially useful candidate for such a "bulb" is a ________. Radio astronomer can measure the distance to a galaxy by noting the width of it 21-cm hydrogen line and applying the _______.
-Andromeda -cepheids -the Hubble space telescope -type la supernova -tully-fisher relation
the first person to observe that our galaxy is disk-shaped was _________. In the 20th century, _______ used the distances and directions of many _______ clusters to map out the Milky Way and show that our solar system was not in the center. Part of the difficulty in observing the galaxy is that we are in the main disk and there is a lot of ______ in the disk, obscuring our view. Today astronomers have observed the distant regions of the galaxy and know that near the middle, stars are not confined to the disk but are distributed in ________
-William Herschel -Harlow Shapley -globular -dust -a central bulge
with modern telescopes, astronomers can observe galaxies that are, as the Star Wars movies say, "far, far away" They need large telescopes, because these distant galaxies appear very __________. One advantage of looking at galaxies really far away is that we see them far ____________, allowing us to figure out the evolution of galaxies. Astronomers calculate the distance to a far- away galaxy by measuring its ___________. For galaxies that are too far away to get a spectrum, they look at the galaxy's overall _________ to get a sense of what kind of stars it is dominated by. From its oldest constituents, astronomers estimate the age of the Milky Way galaxy to be at least ________ years and other galaxies probably also started being formed that long ago.
-faint -back in time -redshift -color -13 billion
astronomers are now able to observe the center of the Milky Way galaxy, not with visible light but with radio waves and _______. At the center, there is a strong radio source which is called ______. At the heart of this radio source, astronomers find a region crowded with stars, all orbiting very fast around _____. Closer in than the stars is ______, which is revealed by very-high resolution radio measurement, and from which material can fall into the very center.
-infrared rays -Sagittarius A* -a supermassive black hole -an accretion disk
put the following methods that astronomers use to find distances to galaxies in order of how far out into the universe they can be applied, from nearest to the farthest
-planetary nebulae used as standard bulbs -cepheid variable stars and the period-luminosity relationship -the width of 21-cm hydrogen lines and the Tully-fisher relation -galaxy redshifts and Hubble's law
put the following things that astronomers can observe in order of distance from the nearest to the farthest
-pluto and its moon charon -the center of the Milky Way galaxy -the Andromeda galaxy (M31) -the most distant Cepheid astronomers can observe -the most distant galaxy in which we have seen a type la supernova
the astronomer Vesto Silpher at the Lowell observatory was the first show, in the 1910's, that (except for those in the same group with us ) all other galaxies showed a ___________ in their spectra. By the 1920's, Edwin Hubble (later assisted by ________________) was able to show this for many more galaxies. They were able to measure the distances to nearby galaxies using _______________. Comparing the two kind of measurements, they found that the ________ of a galaxy was proportional to its distance, a rule that became known as ________. This implied that the entire universe was expanding. Today astronomers understand the movement of the galaxies away from each other is a result of ______________.
-redshift -Milton Humason -Cepheid bearable stars -speed -Hubble's law - the stretching (expansion) of space
Edwin Hubble divided galaxies into types by their shape. Those galaxies that were flat and had arms or lanes of stars were called_______. Rounder galaxies were given the name ______, and galaxies whose shape did not fit an easy pattern and that were generally a bit less massive than the other two types were called _____. The galaxies that generally have almost no gas and dust in them are the ___________. But Hubble's classification scheme was done before the discovery of _____, who gravity may play a significant role in the evolution of galaxies, even though at present we can't see it.
-spirals -ellipticals -irregulars -ellipticals -dark matter
put the following objects or regions in order by mass/light ratio, from the largest value of the ratio to the smallest:
-the coma cluster of galaxies -the local group of galaxies -the disk of the Milky Way galaxy -the Orion spur in which the sun is located -the solar system
put the following objects or regions in order by mass/light ratio, from the lowest value of the ratio to the highest:
-the sun - the total mass of the Milky Way galaxy -small groups of galaxies -ruch clusters of galaxies -the dark matter halo of the Milky Way galaxy
which type of galaxy is very difficult to see, but (astronomers recently realized) may be very common?
dwarf elliptical
the reason type la supernovae are useful to astronomers for determining distances to other galaxies is that
they are very bright, and generally reach the same peak luminosity
