ASTR 121 Exam 3/Final

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

What fraction of the Galaxy's mass is in a form that does not emit electromagnetic radiation?

about 85%

According to density-wave theory, spiral arms are blue because they

contain a lot of young stars formed from clouds comprised by the density wave

Where should you see open clusters in the Milky Way on the sky?

in the disk

Why is it not possible to use visible light to investigate the center of our Galaxy?

intervening gas located in the disk of the Galaxy blocks out view of the galactic center

Why do we call dark matter "dark"?

it does not emit or absorb light of any wavelength that we have been able to detect

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 the material has fallen in for billions of years

Astronomers can measure the diameter of our Milky Way Galaxy by plotting the position of globular star clusters.

true

The Milky Way shows evidence that over its history it has merged with and "cannibalized" smaller galaxies.

true

What have we learned from the work of Harlow Shapely 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

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

Of the normal matter in the Milky Way, the vast majority of the mass is in the form of gas and dust.

false

The Milky Way is titled on the sky because

the solar system is tilted compared to the disk of the galaxy

The estimated age of the Milky Way galaxy is about

13 billion years

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 Earth is located, how should his address end?

Orion Spur

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

Sagittarius A

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 wavelength

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 event horizon of such a supermassive black hole me?

about 35 times the size of the Sun (0.3 AU)

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

The Population I stars in the Milky Way Galaxy

all of these options

Astronomers now know that surrounding the main body of our galaxy and our fainter halo stars there is

an invisible halo made of what astronomers are calling "dark matter"

How does the Milky Way rate?

differentially

One of the reasons Kapetyn underestimated the size of the Milky Way and Shapely overestimated it is that they did not recognize the ____.

dimming effect of interstellar dust

Which are thought to be very young?

giant molecular cloud, group of O and B stars, open cluster

Which are thought to be very old?

globular cluster, planetary nebulae

Which occur only in the parts of the Galaxy other than the spiral arms?

globular cluster, planetary nebulae

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

Which only occur in spiral arms?

group of O and B stars, open cluster, giant molecular cloud

Which have the hottest stars?

group of O and B stars. some giant molecular clouds, young open clusters, planetary nebulae

Rotational velocity outside the visible boundary of our Galaxy is ____ than would be expected on the bassi of observed stars and gas, indicating presence of ____.

higher, dark matter

If I want to find a sizable 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

Where should you look for the youngest stars in the Milky Way Galaxy>?

in the disk

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

Which of the following statements about the spiral arms of the Milky Way is true?

the arms are populated by a large number of O and B type stars and they are sites of recent and ongoing star formation

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

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.

Recently, astronomers have observed stars and other objects that orbit the center of the Milky Way Galaxy farther our than our Sun, but more 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