Problem Set 9B

In the time-lapse movie by Andrea Ghez and collaborators, one of the stars comes within 90 AU of a massive object in the center of the galaxy. From the orbit of that star and of the other neaby stars, the mass within that 90 AU orbit is computed to be about

4 million times time mass of the sun

21-cm radio radiation is emitted by

cold hydrogen gas

In which part of the Milky Way galaxy is the Sun?

disk

The galactic halo contains about as much gas and dust as the galactic disk.

false

What kind of radiation is used to find the location and shape of the Milky Way's spiral arms?

radio waves

In what part of the galaxy are O and B stars most often found?

spiral arms

The Milky Way is

spiral galaxy

The effect of gravitational waves has been seen in

the loss of energy in a binary system of two neutron stars

Herschel's attempt to map the Milky Way by counting stars led to an inaccurate estimate of the Galaxy's size because he was unaware of absorption by interstellar dust.

true

What shows that the mass of the Milky Way extends beyond the visible disk?

Mass deduced from orbits of globular clusters and stars outside the visible disk.

Most of the mass of the Milky Way galaxy is known to be

What constitutes most of the Milky Way's mass is not known.

The large mass in the center of the Milky Way within a radius twice that of Pluto's orbit is the strongest evidence for

a supermassive black hole at the galactic center

21-cm light is associated with

an electron flipping its spin in a hydrogen atom

About how far is the Sun from the center of the Milky Way?

30,000ly

Match the following objects to the part of the galaxy in which they are ordinarily found 1. global clusters 2. open clusters 3. supermassive black hole 4. gas and dust

1-halo 2- disk and bulge 3-bulge, but not the disk 4- disk and bulge

The following features of space and time appeared obvious to people who could travel and measure distances small compared to the size of the Earth. They have had to be discarded as we learned more about the universe. Order them from 1 to 3 according to the order in which they were discarded (1 = first to be discarded, 3 = last to be discarded).

1. earth is flat 2. earth at rest 3. space is flat

What is the diameter of the disk of the Milky Way?

100,000 ly

How long does the Sun take to orbit the galaxy?

225 million years

According to Figure 14.6 of the 6th edition (also Fig. 14.6, fourth and fifth editions), a Cepheid variable with luminosity 1000 times that of the Sun has a period of roughly

3 days

Gravitational waves are a consequence of

Einstein's law of gravity, but not of Newton's