Question 1

A starburst galaxy appears to be a galaxy in which

Accepted Answer

A starburst galaxy is characterized by an exceptionally high rate of star formation, often triggered by interactions or collisions with other galaxies.

Question 2

Which single major problem perhaps concerns astronomers the most as they attempt to interpret the properties and behavior of clusters of galaxies?

Accepted Answer

This is known as the "missing mass problem" or dark matter problem. It is a major concern for astronomers trying to understand the stability and behavior of galaxies and galaxy clusters. The fact that there appears to be much more mass present than can be accounted for by visible material suggests the existence of an unknown form of matter, which is still being studied and researched by scientists. The other options are also areas of interest and study, but not considered to be the single most concerning problem for astronomers.

Question 3

The rotation curve of a galaxy is a graph showing the galaxy's speed of rotation at different distances from the center.The observed rotation curve in the outer parts of a typical large spiral galaxy

Accepted Answer

The observed rotation curve in the outer parts of a typical large spiral galaxy is quite flat, meaning that the speed of rotation remains roughly the same at all distances. This is unexpected according to the laws of Newtonian physics, and suggests the presence of dark matter in the outer regions of the galaxy.

Question 4

In order for gravitational lensing of a distant quasar to occur,the galaxy producing the lensing must

Accepted Answer

Gravitational lensing occurs when a massive object, such as a galaxy or cluster of galaxies, bends the path of light from a more distant object, such as a quasar. For the lensing to occur, the massive object must be almost perfectly aligned between the distant object and the observer on Earth.

Question 5

The fact that quasars can be detected from distances where even the biggest and most luminous galaxies cannot be seen means that they

Accepted Answer

The question states that quasars can be detected from distances where even the biggest and most luminous galaxies cannot be seen. This means that quasars must be intrinsically far more luminous than the brightest galaxies in order for us to detect them from such great distances.

Question 6

In observations of a double-quasar image produced by gravitational lensing,fluctuations on the intensity of one image appear to be delayed compared to equivalent variations on the other image.Why is this?

Accepted Answer

Gravitational lensing causes the path of light to bend as it passes through a massive object, resulting in two images of the same source being observed. However, due to the bending of the light, the path length for each image is different, resulting in a time delay between the two images. Therefore, the optical path through the gravitational lens producing one image is longer than that for the other image.

Question 7

How are clusters of galaxies spread throughout the universe?

Accepted Answer

The distribution of clusters of galaxies in the universe is not random, but rather organized into structures. The largest structures are composed of clusters of galaxies organized around vast empty regions known as voids, giving the universe a cellular or foam-like appearance. This is also known as the cosmic web.

Question 8

The specific characteristics that identify most quasars are

Accepted Answer

Quasars are known for their star-like appearance, very high redshifts (due to the Doppler effect), and large distances from Earth, indicating extremely energetic sources.

Question 9

As much as 90% of the matter in the universe may be unseen "dark matter." Where is this dark matter?

Accepted Answer

Observations of galaxy cluster dynamics and gravitational lensing suggest that dark matter is concentrated in spherical haloes around galaxies, but extends far beyond the visible matter. This is known as the "dark matter halo".

Question 10

What is the likely fate of our Milky Way Galaxy within about the next 6-8 billion years?

Accepted Answer

Current observations suggest that the Milky Way and Andromeda Galaxy are on a collision course and will merge in about 6-8 billion years. This will trigger the formation of new stars in gas and dust clouds, and the two galaxies will eventually merge into a single elliptical galaxy.

Question 11

What evidence is there for considerable extra mass within galaxies that does not produce visible light,the so-called "dark matter?"

Accepted Answer

The rotation curve of galaxies, showing orbital speeds of material, remains flat to large distances from the galactic centers and does not follow a Keplerian curve. This indicates the presence of extra mass that does not produce visible light, the so-called "dark matter."

Question 12

Dark matter in clusters of galaxies

Accepted Answer

Observations of gravitational lensing and galaxy motions within clusters suggest that the majority of the dark matter is distributed around galaxies rather than uniformly within the cluster or in voids between galaxies. This is known as the "galaxy bias" of dark matter.

Question 13

The extreme redshifts of quasar spectra are caused by

Accepted Answer

The extreme redshifts of quasar spectra are caused by very high recession speeds of the sources away from our Galaxy, as predicted by Hubble's law.

Question 14

What would happen if the Andromeda Galaxy (a spiral about the same size as ours)collided with our own Milky Way Galaxy?

Accepted Answer

When the Andromeda Galaxy collides with the Milky Way, the vast distances between stars mean they are unlikely to collide directly. However, the interstellar gas and dust clouds within the galaxies will interact, potentially triggering new star formation as they become heated and compressed.

Question 15

Collisions between galaxies

Accepted Answer

Collisions between galaxies can last hundreds of millions of years due to the massive size of galaxies and the slow speed at which they travel. These collisions can lead to changes in the structures of the galaxies involved, such as the formation of new stars and the disruption of existing ones.

Question 16

Which of the following astronomical objects can be described as follows: "Starlike in appearance;a spectrum showing very high redshift;and energy output of about 1000 galaxies from a small region about 1 light-year across"?

Accepted Answer

The high redshift in the spectrum and the extremely high energy output suggest a quasar, which is a type of active galactic nucleus powered by a supermassive black hole. The other options do not exhibit these characteristics.

Question 17

Which one of the following statements is TRUE about clusters of galaxies?

Accepted Answer

The mass observed in galaxies of a cluster is significantly less than what is needed to hold the cluster together, indicating the presence of dark matter to account for the gravitational forces at play.

Question 18

What is believed to be the origin of giant elliptical galaxies?

Accepted Answer

Giant elliptical galaxies are believed to have formed through galactic cannibalism, where they grew by devouring smaller galaxies. This is supported by observations of giant elliptical galaxies that show evidence of multiple mergers with other galaxies.

Question 19

What percentage of the mass required by the cluster's observed gravity,as shown by the speeds of galaxies in the cluster,is represented by the mass of the presently observable matter in a typical rich cluster of galaxies?

Accepted Answer

The mass of the presently observable matter in a typical rich cluster of galaxies represents only about 10% of the mass required by the cluster's observed gravity, as shown by the speeds of galaxies in the cluster. This discrepancy is one of the pieces of evidence for the existence of dark matter, which does not emit light or radiation that we can currently detect.

Question 20

One of the consequences of the collision of two galaxies appears to be

Accepted Answer

When two galaxies collide, their clouds of gas and dust can collide and trigger the formation of new stars. This can result in a burst of vigorous star birth.

Quiz 14: Investigating Other Galaxies