MA #7

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

1,000 light-years

Suppose that you measure a galaxy's redshift, and from the redshift you determine that its recession velocity is 30,000 (3×10^4) kilometers per second. According to Hubble's law, approximately how far away is the galaxy?

1.4 billion light-years

If we represent the Milky Way Galaxy as the size of a grapefruit (10-cm diameter), the distance to the Andromeda Galaxy would be about

3 m.

Massive-star supernovae and white-dwarf supernovae work equally well as standard candles for measuring cosmic distances.

False

High angular momentum leads to faster rotation. Why does faster rotation tend to lead to a spiral galaxy, rather than an elliptical galaxy?

Faster rotation leads to collisions among gas particles that cause the gas to settle into a spinning disk, rather than a more spread out cloud.

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

It absorbs visible, ultraviolet, and some infrared light.

Based on what you have learned, which of the following best describes the meaning of Hubble's constant (Ho)?

It describes the expansion rate of the universe, with higher values meaning more rapid expansion.

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

100,000 light-years

Suppose a collision strips gas out of a spiral galaxy. Why would this tend to change the spiral galaxy into an elliptical galaxy?

A galaxy cannot have a disk if it does not have gas.

Why are Cepheid variables important?

Cepheids are pulsating variable stars, and their pulsation periods are directly related to their true luminosities. Hence, we can use Cepheids as "standard candles" for distance measurements.

What causes the glow of the reddish areas visible primarily in the spiral arms?

Clouds of gas are being heated by ultraviolet light from nearby, recently formed stars.

You observe the peak brightnesses of two white dwarf supernovae. Supernova A is only one-quarter as bright as Supernova B. What can you say about their relative distances?

Supernova A is twice as far away as Supernova B.

How do we know that halo stars are older, on average, than disk stars?

There are no blue halo stars.

Consider the four features of spiral arms that you identified in Part A. What do they all have in common that explains why they are found together in spiral arms?

They are all associated with star formation.

What makes up the interstellar medium?

gas and dust

What kinds of objects lie in the halo of our galaxy?

globular clusters

Based on the association of star formation with spiral arms, we can conclude that the gas in spiral arms __________ than it does in regions between the arms.

has greater density

Where are most heavy elements made?

in stars and supernovae

The Sun's location in the Milky Way Galaxy is

in the galactic disk, roughly halfway between the center and the outer edge of the disk

Harlow Shapley concluded that the Sun was not in the center of the Milky Way Galaxy by

mapping the distribution of globular clusters in the galaxy.

Which of the following sequences lists the methods for determining distance in the correct order from nearest to farthest?

parallax, Cepheid variables, Hubble's law

What is the most accurate way to determine the distance to a nearby galaxy?

using Cepheid variables

How was Edwin Hubble able to use his discovery of a Cepheid in Andromeda to prove that the "spiral nebulae" were actually entire galaxies?

From the period-luminosity relation for Cepheids, he was able to determine the distance to Andromeda and show that it was far outside the Milky Way Galaxy.

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

Gas and dust are abundant in the disk but not in the halo. Clusters of young stars are found only in the disk. Stars in the disk all orbit in the same direction and nearly the same plane, while halo stars have more randomly oriented orbits. Disk stars come in a broad range of masses and colors, while halo stars are mostly of low mass and red.

How did Edwin Hubble measure the distance to the Andromeda Galaxy?

He applied the period-luminosity relation to Cepheid variables.

High density tends to lead to more rapid star formation in a protogalactic cloud. Why does this rapid star formation tend to lead to an elliptical galaxy, rather than a spiral galaxy?

Rapid star formation means that there may not be enough gas left to make a disk.

The patterns on the graph of galaxy colors and luminosities allow scientists to make inferences about galaxy evolution. Which of the following statements accurately reflect current scientific thinking about galaxy evolution based on these data?

Some large red galaxies arose from mergers of smaller blue galaxies. All galaxies start their lives as members of the blue cloud. Very large galaxies tend to use up the gas available for star formation more rapidly than smaller galaxies.

Which of the following best describes what spiral arms are?

Spiral arms are waves of higher density that move outward through a galaxy, triggering star formation as they pass.

Select the сorrect statements. The Milky Way is not wider than it's thickness. We see stars distributed more or less evenly across the sky. Shapley's 20th-century observations of globular cluster orbits, which center on a point about 30,000 light years from our Sun, showed we were in the center of the galaxy. The Milky Way is much wider than it's thickness. So it is a narrow band with many stars in it, while the sky outside the band has much fewer stars. Shapley's 20th-century observations of globular cluster orbits, which center on a point about 30,000 light years from our Sun, showed we weren't in the center of the galaxy.

The Milky Way is much wider than it's thickness. So it is a narrow band with many stars in it, while the sky outside the band has much fewer stars. Shapley's 20th-century observations of globular cluster orbits, which center on a point about 30,000 light years from our Sun, showed we weren't in the center of the galaxy.

What makes white-dwarf supernovae good standard candles?

They are very bright, so they can be used to determine the distances to galaxies billions of light-years away. They should all have approximately the same luminosity.

White-dwarf supernovae are good standard candles for distance measurements for all the following reasons except which?

White-dwarf supernovae occur only among young and extremely bright stars.

Which types of galaxies have a clearly defined halo component?

all but irregulars

What do astronomers consider heavy elements?

all elements besides hydrogen and helium

What kinds of objects lie in the disk of our galaxy?

all of the above

What is a standard candle?

an object for which we are likely to know the true luminosity

We can always determine the recession velocity of a galaxy (at least in principle) from its redshift. But before we can use Hubble's law, we must first calibrate it by

measuring the distances to many distant galaxies with a standard candle technique

What evidence supports the idea that a collision between two spiral galaxies might lead to the creation of a single elliptical galaxy?

observations of giant elliptical galaxies at the center of dense clusters that may have grown by consuming other galaxies observations of some elliptical galaxies with stars and gas clouds in their cores that orbit differently from the other stars in the galaxy the fact that elliptical galaxies dominate the galaxy populations at the cores of dense clusters of galaxies observations of some elliptical galaxies surrounded by shells of stars that probably formed from stars stripped out of smaller galaxies

Compared to spiral galaxies, elliptical galaxies are

redder and rounder.

The disk component of a spiral galaxy includes which of the following parts?

spiral arms

What is the most accurate way to determine the distance to a nearby star?

stellar parallax

Hubble's law expresses a relationship between

the distance of a galaxy and the speed at which it is moving away from us

If you were to take a voyage across the Milky Way, what kind of material would you spend most of your time in?

warm, rarefied clouds of atomic hydrogen

Which of the following are you more likely to find within (or on the edges of) spiral arms of a spiral galaxy than in between these arms?

young stars dense, dusty gas clouds ionization nebulae massive stars (spectral types O and B)