AST 115 Final Exam

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 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

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

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

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

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

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

where would you look for the youngest stars in the Milky Way galaxy?

in the disk

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

the stellar halo

its stars were born a long time ago (13 billion years)

the very strong source of radio waves at the center of our galaxy is called

sagittarius A

our Milky Way galaxy is what type of galaxy?

spiral

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

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

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

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

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

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

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