Exam 15: Our Galaxy

Over time, what is the net effect of the star- gas- star cycle in the Milky Way?

Why do spiral arms have a blue color?

The primary way that we observe the atomic hydrogen that makes up most of the interstellar gas in the Milky Way is with _.

What are the Magellanic Clouds?

Why has star formation ceased in the galactic halo?

How does the interstellar medium obscure our view of most of the galaxy?

If we could see our own galaxy from 2 million light- years away, it would appear _ .

Which of the following are signposts of the presence of high mass stars, and thus recent star formation?

Astronomers observe huge bubbles of hot gas, some over a thousand light years across, in the Milky Way. What is their cause?

Modified Newtonian Dynamics? The case for dark matter in the Milky Way can be viewed as a failure of stars and gas far from the galactic center to obey Newton's law of gravitational attraction-- that is, the stars and gas seem to orbit too quickly for the visible matter their orbits enclose. Why do you think that astronomers choose to "save" Newton's form of gravitational attraction by postulating unseen dark matter, as opposed to regarding the observed orbital motion as a falsification of Newtonian gravitation on the scale of the Milky Way? [Note: At the distance scales involved, the gravitational forces in the galaxy are all fairly weak, much weaker than those encountered in a neutron star or black hole, and hence Einstein's theory of gravity (General Relativity)gives the same predictions as Newton's gravitational law].

Briefly explain why stars that formed early in the history of the galaxy contain a smaller proportion of heavy elements than stars that formed more recently.

What evidence supports the existence of a black hole at the center of our galaxy?

Red and orange stars are found evenly spread throughout the galactic disk, but blue stars are typically found .

How did star formation likely proceed in the protogalactic cloud that formed the Milky Way?

Inferring cloud properties using carbon- monoxide: At the low temperatures of molecular clouds, carbon monoxide emits radio light more strongly than does molecular hydrogen. What assumptions must be made to then use observations of carbon monoxide to infer the properties of the cloud as a whole?

What is Sgr A×?

Spectra for the Cygnus loop and the Orion nebula are shown above. Which of these is seen in the Orion nebula, but is not clearly visible in the Cygnus loop spectrum?

Which star is older?

Which kind of star is highly unlikely to be found in the halo of the Milky Way?

Explain why in space, "no one can hear you scream."