chap 25

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

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

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

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

in the disk

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

Our Milky Way Galaxy is what type of galaxy?

spiral

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

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

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

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?

we still see material falling toward the center and material has fallen in for billions of years