Chapter 25 & Chapter 26 Astronomy Test

Dark matter is believed to make up approximately 90% of the matter in the universe. This is based on various observations and measurements that suggest the existence of dark matter, even though it cannot be directly observed or detected through electromagnetic radiation. Scientists have studied the gravitational effects of dark matter on visible matter and the large-scale structure of the universe, leading to the estimation that dark matter contributes significantly to the total mass and energy content of the universe.

The correct answer is "tens". This means that the most massive galaxies have tens of times more stars than the Milky Way. This suggests that these galaxies have a significantly larger number of stars compared to our own galaxy. The answer "10's" is an alternative way of representing the word "tens".

If the density of the universe is less than critical, it means that there is not enough matter and energy to counteract the expansion of the universe. This would result in a scenario known as "cold death" or "heat death." In this scenario, the universe would continue to expand and cool down until all the stars burn out and all matter is too spread out to form new stars or galaxies. It would be a state of maximum entropy and complete darkness, with no possibility of any further activity or life.

The Hubble law implies that the universe has always been expanding. This law states that the farther a galaxy is from us, the faster it is moving away. This suggests that if we were to rewind time, galaxies would have been closer together in the past. The expansion of the universe is supported by various observations, such as the redshift of light from distant galaxies and the cosmic microwave background radiation. Therefore, the Hubble law indicates that the history of the universe involves a continuous expansion.

Collisions between galaxies do not have a larger effect on the individual stars. In fact, during galactic collisions, the vast majority of stars in each galaxy pass by each other without colliding. The space between stars is so vast that the likelihood of two stars directly colliding is extremely low. However, the gravitational interactions between galaxies can cause the gas and dust within them to collide, triggering star formation and altering the overall structure of the galaxies.

The term "isotropic" refers to a property or characteristic that is uniform or consistent in all directions. In the context of the question, it means that the universe has the same properties, such as temperature or density, regardless of the direction in which it is observed. This implies that there is no preferred direction or orientation in the universe, and it is homogeneous on a large scale.

It is not correct to think of everything moving away from a central point in the universe because there is no center. According to the current understanding of the universe, space itself is expanding in all directions, causing galaxies to move away from each other. This expansion is happening uniformly, without a specific central point towards which everything is moving. Therefore, the concept of a central point in the universe is not supported by scientific evidence.

A "closed universe" refers to a scenario in which space is curved or bent to such an extent that it forms a closed shape, similar to a sphere. This means that if you were to travel in any direction in this universe, you would eventually return to your starting point. The concept of a closed universe suggests that the overall geometry of the universe is finite and bound, rather than infinite and open-ended.

In the critical universe now proposed, the ratio of matter to energy is 27/73. This means that for every 27 units of matter, there are 73 units of energy. This ratio is important in understanding the composition and balance of the universe. It suggests that energy is more dominant than matter in the critical universe.

The statement suggests that there is gravitational evidence pointing towards the existence of dark galaxies, even though they have not been observed directly. This implies that scientists have detected gravitational effects that can only be explained by the presence of unseen dark galaxies. Therefore, the correct answer is true.

Collisions between galaxies are not rare, in fact, they are quite common in the universe. Galaxies can collide and merge due to the gravitational forces between them. These collisions often result in dramatic changes in the structure and appearance of the galaxies involved. Therefore, the statement that collisions between galaxies are rare is incorrect.

Homogeneous is the correct answer because it refers to the concept that all large samples of the universe are alike in appearance everywhere in the universe. This means that no matter where you look in the universe, the properties and characteristics of the samples will be the same.

The term "red shift" refers to the phenomenon where light from distant objects in space appears to be shifted towards longer wavelengths, towards the red end of the spectrum. While there can be various factors that cause red shifts in the spectrum, the specific red shift associated with the expansion of the universe is known as cosmological red shift. This is because as the universe expands, the space between galaxies also expands, causing the wavelengths of light to stretch and appear more red. Therefore, the correct answer is cosmological.

Quasars do not necessarily end in a massive explosion as a gamma ray burst. While quasars are extremely bright and energetic objects powered by supermassive black holes, they eventually run out of fuel and fade away rather than exploding. Gamma ray bursts, on the other hand, are highly energetic explosions that occur in distant galaxies and are believed to be caused by the collapse of massive stars. Therefore, the statement that quasars end in a massive explosion as a gamma ray burst is false.

Recent work with Type I supernovae at great distances suggests the universe may in fact be accelerating its expansion, a discovery attributed to the newly found age. This means that the age of the universe plays a crucial role in understanding its expansion. The discovery of the universe's age has provided valuable insights into the understanding of the accelerating expansion phenomenon.

The satellite most responsible for studying the microwave universe and the nature of the cosmic background radiation is likely to be the one represented by the combination of letters "CBE". This is because the other options, "CCE" and "CDE", do not specifically mention studying the microwave universe or cosmic background radiation. Therefore, "CBE" is the most appropriate choice for the satellite responsible for such studies.

Determining the rotation curves of nearby spiral galaxies is the best method for determining their mass. This is because the rotation curves provide information about how the stars and gas in the galaxy are moving at different distances from the center. By studying the rotation curves, scientists can infer the distribution of mass within the galaxy and calculate its total mass. This method is more reliable than determining the distance or amount of matter directly, as it takes into account the gravitational effects of all the mass in the galaxy, including dark matter.

The statement suggests that there are no quasars within a billion light years of us, implying that the last quasar died out a billion years ago. However, this is not necessarily true. The absence of quasars within a billion light years does not guarantee that the last quasar died out a billion years ago. It is possible that there are quasars beyond this distance or that new quasars could form in the future. Therefore, the answer is false.

When galaxies collide, the individual stars within the galaxies are not directly affected. Although the galaxies may experience gravitational interactions and distortions, the stars themselves are so far apart that they usually do not collide or merge. The stars continue to follow their own orbits within their respective galaxies, unaffected by the collision. Therefore, there is no direct effect on individual stars when galaxies collide.

According to the best current theory, the formation of the first quasars occurred 13 billion years ago. This implies that these extremely bright and distant celestial objects originated approximately 13 billion years after the Big Bang. Quasars are believed to be powered by supermassive black holes, and their formation is closely linked to the early stages of galaxy evolution in the universe.

Seyfert galaxies may bridge the gap between spiral galaxies and quasars. Seyfert galaxies are a type of active galaxy that have a bright nucleus and show evidence of a supermassive black hole at their center. They exhibit characteristics of both spiral galaxies, such as a disk-like structure, and quasars, which are extremely luminous and powered by accretion onto a black hole. This suggests that Seyfert galaxies may represent an intermediate stage in the evolution of galaxies, providing a link between the two types.

There are an estimated 40 billion galaxies in the observable universe. This estimation is based on observations made by astronomers using advanced telescopes and other instruments. The observable universe refers to the part of the universe that we are able to see and study from Earth. It is believed that there may be many more galaxies beyond the observable universe, but they are currently beyond our reach of observation.

The statement suggests that the majority of mass for most galaxies is located in their dark halos. However, this is not true. Current scientific understanding indicates that the majority of mass in galaxies is actually in the form of dark matter, which is not concentrated in the halos but rather distributed throughout the galaxy. Therefore, the correct answer is false.

The correct answer is "We see it ten billion years away." When we observe a galaxy that is one billion light years away, we are actually seeing it as it existed ten billion years ago. This is because light takes time to travel through space, so the light we receive from distant objects is a snapshot of how they appeared in the past. Therefore, the further away an object is, the further back in time we are observing it.

Spiral galaxies are rare in the center of clusters because they tend to be more common in the outskirts of clusters. In the dense environment of the cluster center, interactions between galaxies are frequent and can disrupt the delicate structures of spiral galaxies, transforming them into other types of galaxies such as elliptical or irregular. Therefore, the presence of spiral galaxies in the center of clusters is relatively uncommon.

The H-R diagram turn-off point refers to the point on the diagram where stars begin to leave the main sequence and evolve into red giants. The age of a globular cluster can be estimated by determining the turn-off point of its stars. The given answer suggests that the oldest globular clusters are approximately 3-4 billion years old based on their turn-off points.

The correct answer is "Crowding." When two galaxies collide, the outcome depends on the density of stars and gas within them. If the galaxies are densely populated, the gravitational forces between the stars and gas will cause them to interact and merge together. This crowding leads to the merging of the galaxies. However, if the galaxies have low density, they are more likely to pass through each other without merging. Therefore, crowding plays a crucial role in determining whether colliding galaxies will stick and merge or simply pass through each other.

Quasars are extremely luminous and powerful objects that are fueled by the supermassive black holes at their centers. They emit vast amounts of energy and are thought to be powered by the accretion of matter onto the black hole. Due to the immense amount of energy released, it is estimated that a quasar can only last for a finite amount of time before running out of fuel. The most plausible estimate for the duration of a quasar's energetic phase is two billion years.

The radius of a black hole is determined by its mass. A billion solar mass black hole is extremely massive, resulting in a larger radius compared to smaller black holes. Since the question asks for the radius in astronomical units (A.U), which is a unit of distance, it implies that the radius is relatively large. Among the given options, the closest value to a large radius is "About 20 A.U." Therefore, this is the correct answer.

Super-massive galaxies are often found at the cores of rich galaxy clusters because of cannibalism. Cannibalism refers to the process in which smaller galaxies are consumed by larger galaxies, causing the larger galaxies to grow in size. In rich galaxy clusters, there is a high density of galaxies, increasing the likelihood of interactions and mergers between galaxies. As a result, super-massive galaxies form at the cores of these clusters through the accumulation of smaller galaxies over time.

Active galaxies, such as quasars and Seyfert galaxies, have highly energetic central regions. These regions are powered by the accretion of material onto a supermassive black hole at the galaxy's center. This material, often in the form of gas and dust, acts as fuel for the black hole, providing the necessary mass and energy to generate the intense radiation and jets of particles observed in active galaxies. Therefore, the correct answer is "Fuel."

The black hole at the center of an active galaxy or quasar requires fuel to radiate massive amounts of energy. This fuel refers to the material, such as gas and dust, that is being consumed by the black hole. As this matter falls into the black hole, it releases a tremendous amount of energy in the form of radiation. This fueling process is what powers the intense brightness and activity observed in active galaxies and quasars.

When galaxies collide, the gravitational forces between them cause the stellar contents to be rearranged. This means that stars from both galaxies can be pulled out of their original positions and end up in new locations. Additionally, the interstellar contents, which include gas and dust, are also rearranged during these collisions. This can lead to the formation of new stars and the disruption of existing star-forming regions. Therefore, the correct answer is that collisions between galaxies result in the rearrangement of both the stellar contents and the interstellar contents.