Milky Way

The circular but relatively flat portion of the galaxy is the ________ - halo - bulge - disk - spiral arm - spiral galaxy - globular cluster

The first portion of the galaxy to form was the _______ - halo - bulge - disk - spiral arm - spiral galaxy - globular cluster

A tightly packed group of a few hundred thousand very old stars is a _________ - halo - bulge - disk - spiral arm - spiral galaxy - globular cluster

A _________ stands out in a photo of a galaxy because it shines bright with light from massive young stars and glowing clouds of gas and dust - halo - bulge - disk - spiral arm - spiral galaxy - globular cluster

Our Milky Way galaxy is a _________ - halo - bulge - disk - spiral arm - spiral galaxy - globular cluster

Stars orbiting in the ________ near the galaxy's center can have orbits highly inclined to the galactic plane

The following figures show several stars found in the disk and halo of the Milky Way Galaxy. Rank the stars based on their current age, from oldest to youngest. If two (or more) stars have approximately the same age (that is, ages within a few million years), rank them as equal by dragging one on top of the other(s).

Listed following are several stars found in the disk and halo of the Milky Way Galaxy. Assume that both the blue and yellow disk stars are members of the same open cluster. Rank the stars based on the abundance of elements heavier than carbon that you would expect to find in each of the stars, from highest to lowest. If you expect two (or more) stars to have approximately the same abundance, rank them as equal by dragging one on top of the other(s).

To calculate the dashed orbits from the stellar positions, astronomers had to assume that __________.

Notice that some of the stars on the diagram are represented by a series of dots that are very close together, while others have their dots farther apart. Keeping in mind that all the stellar positions were measured at one-year intervals, which stars are moving the fastest in their orbits during the time period indicated by the dots?

To determine the mass of the central object, we must apply Newton's version of Kepler's third law, which requires knowing the orbital period and average orbital distance (semimajor axis) for at least one star. Let's consider the star with the smallest orbit, which is represented by red and pink dots. What is the approximate orbital period of this star?

Look again at the orbit of the star with the smallest orbit, represented by red and pink dots. By comparing the orbit to the scale bar shown on the diagram, you can estimate that this orbit has a semimajor axis of about _____.

The following equation, derived from Newton's version of Kepler's third law, allows us to calculate the mass (M) of a central object, in solar masses, from an orbiting object's period (p) in years and semimajor axis (a) in astronomical units: M=a3p2 Using this formula with the values you found in Parts C and D, what is the approximate mass of the central object?

From Part E you know the mass of the central object. Now consider its size. Based on what you can see in the diagram, you can conclude that the diameter of the central mass is __________.

You've now found that the central object has a mass of about 3 million solar masses but is no more than about 70 AU in diameter—which means it cannot be much larger than the size of our planetary system. Why do these facts lead astronomers to conclude that the central object is a black hole?

The image sequence zooms in on the center of the Milky Way Galaxy. Consider the first image in the sequence, which is the image that is zoomed-out as far as possible. Approximately what fraction of the Milky Way's total diameter is spanned by this image?

The sequence of photos in the Interactive Figure consists of infrared and radio images. Why doesn't the sequence include any visible-light images?

Now zoom through the image sequence, looking carefully at each image. Which of the following are reasonable conclusions?

The last image in the sequence shows two arrows pointing to the precise location of Sgr A*, yet the image shows nothing located at that position. Based on your study of the entire sequence, which of the following types of image would most likely allow us to see something at this location?

Astronomers have concluded that Sgr A* is actually a very small but extremely massive object, which is presumed to be a massive black hole. What additional observations or measurements (not shown in this sequence) must have been made for astronomers to reach this conclusion?

Which of the following statements correctly summarize key differences between the disk and the halo?