Astronomy Chapter 19

100,000 light-years

1,000 light-years

globular clusters

All of the above A) open clusters B) O and B stars C) old K and M stars D) gas and dust

globular clusters

gas and dust

warm, rarefied clouds of atomic hydrogen

It absorbs visible, ultraviolet, and some infrared light.

by observing in high-energy wavelengths such as X rays and long wavelengths of light such as radio waves

mapping the distribution of globular clusters in the galaxy.

27,000 light-years

all elements besides hydrogen and helium

in stars and supernovae

Halo stars formed in an environment where there were few heavy elements to create rocky planets.

by the winds of massive stars and supernovae

a very low-density region of interstellar space, formed by the merger of several bubbles

travel much faster than sound on Earth but have such low density that they are inaudible.

a wave of pressure that moves faster than the speed of sound

subatomic particles that travel close to the speed of light

multiple supernovae occurring together

the theory that hot, ionized gas blown out of the galactic disk and into the halo by superbubbles cools down and falls back into the disk

We see hot gas above the disk of the galaxy and cool gas that appears to be raining down from the halo.

atomic hydrogen

atomic hydrogen

in the winds of red giant stars

The image of our galaxy in radio emission from CO, mapping the distribution of molecular clouds, is closest to the image of our galaxy in

infrared emission from interstellar dust grains.

old, red, and dim and have fewer heavy elements.

are elliptical, with random orientation.

230 million years

in the spiral arms

There are no blue spheroidal stars.

Globular cluster ages increase with distance from the Milky Way.

Disk stars are all younger than 5 billion years.

Halo stars are made entirely of hydrogen and helium with no heavy elements.

Halo stars differ in age and heavy-element content, but these variations do not seem to depend on the stars' distance from the galactic center.

Sagittarius

We cannot see the galactic center with visible or ultraviolet light, but radio and X rays from the center can be detected.

at optical wavelengths, we see a cluster of old, red stars

The motions of the gas and stars at the center indicate that it contains a million solar masses within a region only about 1 parsec across.

a source of bright radio emission in the center of our galaxy

They have a smaller proportion of heavy elements