Question 1

About two thirds of the nearby spiral galaxies (which we can study in more detail) don't have a round central bulge, but instead show

Accepted Answer

The majority of nearby spiral galaxies have a central bulge with a bar of stars in the middle, rather than a round central bulge.

Question 2

Our Milky Way Galaxy is what type of galaxy?

Accepted Answer

The Milky Way Galaxy has a spiral shape, with a central bulge and spiral arms extending out from it. This is determined from observations of the distribution of stars and gas within our galaxy.

Question 3

The new instrument that made it possible for Edwin Hubble to demonstrate the existence of other galaxies in the early 1920's was:

Accepted Answer

The new instrument that made it possible for Edwin Hubble to demonstrate the existence of other galaxies in the early 1920's was the 100-inch reflector on Mount Wilson.

Question 4

If a galaxy contains a great deal of dark matter, then, compared to the mass-to-light ratio of the inner part, the mass-to-light ratio of the whole galaxy will be

Accepted Answer

The mass-to-light ratio of the whole galaxy will be more if it contains a great deal of dark matter. This is because dark matter contributes to the mass but not to the light output, increasing the mass-to-light ratio especially in the outer parts where dark matter is more prevalent.

Question 5

What method would astronomers use to find the distance to a galaxy so far away that individual stars are impossible to make out (resolve)?

Accepted Answer

Finding the redshift and using Hubble's Law is the most reliable method to determine distance to very distant galaxies where individual stars cannot be resolved. Hubble's Law relates the distance to the redshift of the galaxy, allowing for an accurate estimation of distances even for galaxies beyond our ability to observe individual stars.

Question 6

Compared to the mass of our own Milky Way Galaxy, the total mass we estimate for the Andromeda Galaxy is

Accepted Answer

The Andromeda Galaxy has a total mass estimated to be around 1.5 trillion times the mass of the sun, which is slightly bigger than the estimated total mass of our Milky Way Galaxy of around 1 trillion times the mass of the sun. Therefore, the best choice is D, somewhat bigger.

Question 7

Which type of galaxy is very difficult to see, but (astronomers recently realized) may be very common?

Accepted Answer

Dwarf elliptical galaxies are very difficult to detect because they are small and have low luminosity. However, recent studies have suggested that they may be the most common type of galaxy in the universe.

Question 8

The type of galaxy that consists almost entirely of old stars and is thus less blue (more yellow and reddish) than the other types is:

Accepted Answer

Elliptical galaxies are made up of mostly old stars, resulting in their yellow and reddish colors. Spiral and irregular galaxies have a mix of old and young stars, making them more blue in color. Barred spiral galaxies have a bar-shaped structure in the center, but still have a mix of old and young stars.

Question 9

Which of the following objects is considered useful to astronomers as a "standard bulb" for determining distances?

Accepted Answer

Type Ia supernovae have a known intrinsic brightness, making them useful as "standard bulbs" for determining distances to far-off galaxies. By observing how bright the supernova appears from Earth, astronomers can calculate its distance by comparing its apparent brightness to its known intrinsic brightness.

Question 10

Which of the following is NOT a characteristic of a spiral galaxy?

Accepted Answer

Spiral galaxies actually have stars with more heavy elements than the Sun because they have gone through more generations of star formation, with each generation producing heavier elements than the one before it. This is known as the "metallicity" of stars, and spiral galaxies have a higher metallicity than many other types of galaxies.

Question 11

Which is one reason that the typical galaxy's mass-to-light ratio (in units of the Sun's mass over the Sun's luminosity) generally greater than 1?

Accepted Answer

Galaxies contain a mix of stars with different masses and luminosities, but on average the majority of stars in a galaxy are smaller and fainter than the Sun. This means that the total mass in a galaxy is higher than the total luminosity, resulting in a mass-to-light ratio greater than 1.

Question 12

Which type of galaxy is observed to contain mostly older stars?

Accepted Answer

Elliptical galaxies are observed to contain mostly older stars, as they formed earlier in the universe's history through mergers and accretion of other smaller galaxies. Spiral galaxies, on the other hand, contain a mix of both old and young stars as they continue to form new stars through ongoing star formation. Dwarf elliptical galaxies are also primarily made up of old stars, but they are much smaller and less massive than their larger counterparts. Irregular galaxies have no specific shape and can contain a mix of old and young stars depending on their history of star formation.

Question 13

The type of galaxy that sometimes has a distinct bar of stars running across the central region is

Accepted Answer

Spiral galaxies are the type that sometimes have a distinct bar of stars running across the central region, hence it is the best choice.

Question 14

Which of the following statements about the different types (shapes) of galaxies is correct?

Accepted Answer

Collisions and mergers between galaxies can cause a change in the galaxy's type or shape. This is why we sometimes see unusual or peculiar galaxies that do not fit into the typical categories of spirals, ellipticals, or irregulars.

Question 15

Among irregular galaxies, what makes the Large and Small Magellanic Cloud especially useful for astronomers?

Accepted Answer

The Large and Small Magellanic Cloud are especially useful for astronomers because they are very close to us, making them easier to study compared to other irregular galaxies that are much farther away.

Question 16

If a galaxy contains a great deal of "dark matter," what will that do the galaxy's mass-to-light ratio?

Accepted Answer

Dark matter does not emit, absorb, or reflect light, making it invisible and undetectable by electromagnetic means. However, it exerts gravitational effects on visible matter, radiation, and the large-scale structure of the universe. Therefore, a galaxy containing a great deal of dark matter will have a significantly higher mass than what is suggested by its visible light alone, thus increasing its mass-to-light ratio quite a bit.

Question 17

Edwin Hubble developed a classification scheme for galaxies. By what characteristic did he classify galaxies?

Accepted Answer

Edwin Hubble classified galaxies based on their shape. He identified three main types of galaxies: elliptical, spiral, and irregular.

Question 18

One of the most important observations in the history of astronomy was the one by Edwin Hubble that established that there are other galaxies, quite removed from the Milky Way. How did Hubble show this?

Accepted Answer

Hubble observed a Cepheid variable in a nearby galaxy (the Andromeda Galaxy) and used it to determine its distance, which showed that it was far beyond the Milky Way and therefore other galaxies existed. This was the first evidence for the existence of the universe beyond the Milky Way.

Question 19

One of the main projects being carried out by the Hubble Space Telescope is to measure the distances of galaxies located in groups dozens of millions of lightyears away. What method do astronomers use with the Hubble to find such distances?

Accepted Answer

Astronomers use Cepheid variables located in distant galaxies to measure their distances with the Hubble Space Telescope. Cepheid variables are stars that pulsate regularly, and their period of pulsation is directly related to their brightness. By measuring the period of these stars in distant galaxies, astronomers can determine their distance using the known relationship between period and brightness.

Question 20

A graduate student in astronomy needs to measure the mass of a spiral galaxy she is studying for her PhD thesis. Which of the following observations would be important for her to make?

Accepted Answer

The most important observation for measuring the mass of a spiral galaxy would be to obtain the speed at which stars or gas near the outer regions of the galaxy are moving around. This can be used in combination with Kepler's laws to calculate the mass of the galaxy. Options A, B, C, and D are not directly related to measuring the mass of the galaxy.

Quiz 26: Galaxies