Question 1

Any asymmetry in the gravity field of a spiral galaxy can create spiral arms.

Accepted Answer

Asymmetry in the gravity field of a spiral galaxy, such as caused by a density wave, can create areas of higher density that lead to the formation of spiral arms.

Question 2

The 3-D shape of an elliptical galaxy depends on the average velocity of its stars along each of the three axes.

Accepted Answer

The 3-D shape of an elliptical galaxy is determined by the distribution of its stars and their movements along each of the three axes. The average velocity of the stars plays a crucial role in defining the shape of the galaxy.

Question 3

Dark matter is distributed inside galaxies in exactly the same way as luminous matter,although the total mass of dark matter is much larger than that of luminous matter.

Accepted Answer

False

Question 4

Although elliptical and irregular galaxies have been observed in both dwarf and giant varieties,we find only giant spiral galaxies.

Accepted Answer

The answer of Although elliptical and irregular galaxies have been...

Question 5

We can determine the three-dimensional shape of any individual elliptical galaxy by photographing it.

Accepted Answer

We cannot determine the three-dimensional shape of an elliptical galaxy just by photographing it. Further observations and measurements are needed to determine its shape and characteristics.

Question 6

The Hubble diagram is a way of sorting galaxies by their visual appearance.

Accepted Answer

The answer of The Hubble diagram is a way of...

Question 7

Galaxies that are classified as quasars were much more numerous in the past.

Accepted Answer

Observations show that quasars were more numerous in the early Universe, around 10 billion years ago, than they are today. This is believed to be due to the fact that quasars are powered by the supermassive black holes at the centers of galaxies, and these black holes were more active in the past.

Question 8

Seyfert galaxies are unique because they have large lobes of radio emission that extend well beyond the visible part of the galaxy.

Accepted Answer

The answer of Seyfert galaxies are unique because they have...

Question 9

Astronomers have evidence that all giant galaxies probably contain supermassive black holes.

Accepted Answer

This statement is true according to current scientific knowledge and observations. Supermassive black holes are thought to be present at the centers of most, if not all, galaxies.

Question 10

Elliptical galaxies have the shapes they do because all the stars are orbiting in the same direction in the galaxy.

Accepted Answer

Elliptical galaxies have a more random distribution of star orbits, resulting in their elliptical shape.

Question 11

Star formation in spiral galaxies is enhanced in the spiral arms because more hot gas is concentrated there.

Accepted Answer

The answer of Star formation in spiral galaxies is enhanced...

Question 12

A galaxy can contain a supermassive black hole that remains invisible because no matter is falling onto the black hole.

Accepted Answer

A supermassive black hole can remain invisible if there is no accretion disk of matter falling onto it, which would emit radiation and make the black hole visible.

Question 13

In most galaxies,the amount of dark matter and the amount of luminous matter is about equal.

Accepted Answer

In most galaxies, the amount of dark matter is actually much greater than the amount of luminous matter. It is estimated that around 85% of the total matter in the universe is actually dark matter.

Question 14

The type of AGN we see depends mostly on the angle at which we view the galaxy.

Accepted Answer

The angle at which we view the galaxy determines the appearance of the central AGN, with some angles resulting in obscured AGN and others resulting in unobscured AGN.

Question 15

We know AGN are about the size of our Solar System because of how fast they change in brightness over time.

Accepted Answer

AGN are known to change in brightness over time, with some fluctuations occurring in a matter of days or even hours. These rapid changes suggest that the source of the light must be very small, on the order of the size of our solar system.

Question 16

Dark matter consists of material that emits radiation at wavelengths other than visible light.

Accepted Answer

Dark matter does not emit any radiation at any wavelength, visible or otherwise. It is called "dark" because it does not interact with light, so it cannot be seen directly through telescopes or other scientific instruments that rely on electromagnetic radiation. Its presence can only be inferred through its gravitational effects on other visible matter.

Question 17

Today in our local universe,approximately 30 percent of galaxies are AGNs.

Accepted Answer

The answer of Today in our local universe,approximately 30 percent...

Question 18

Elliptical galaxies contain hot gas that is heated by supernova explosions.

Accepted Answer

Elliptical galaxies do contain hot gas that is heated by supernova explosions. This gas can be detected by X-ray telescopes.

Question 19

The Hubble tuning fork diagram represents an evolutionary diagram of galaxies from elliptical to spiral.

Accepted Answer

The answer of The Hubble tuning fork diagram represents an...

Question 20

We know that spiral galaxies contain dark matter because the gas in the disk rotates with a velocity that decreases in a way that is proportional to r^-1/2.

Accepted Answer

The rotation curves of spiral galaxies remain flat or even rise at large radii, rather than decreasing as expected if only visible matter were present. This discrepancy suggests the presence of dark matter.

Quiz 20: Galaxies