which characteristics are considered most typical of an old galaxy in decline?

Question

very bright, relatively small
low gas content, little star formation
shrinking in size, high dust content
spiral, abundant planets present

Answer 1

The most typical characteristics of an old galaxy in decline are:

1. Low gas content and little star formation: As galaxies age, they tend to use up their available gas resources, resulting in a decrease in star formation activities. This leads to a decline in the number of young, hot stars.

2. Shrinking in size and high dust content: An old galaxy in decline may undergo a process called galactic cannibalism, where it merges with other galaxies and accumulates more dust and material. This can cause the galaxy to shrink in size over time due to the gravitational interactions between the merging galaxies.

3. Relatively small and less bright: Older galaxies generally have lower levels of ongoing star formation and fewer young, massive stars. As a result, their overall brightness tends to decrease compared to younger, more active galaxies. Additionally, the merging and cannibalism processes can lead to the formation of smaller, compact galaxies.

4. Spiral structure and abundant planets: Although spiral galaxies can exist in various stages of their lifetimes, a decline in an old galaxy may still retain its spiral structure. Additionally, over time, planets could have formed around stars in the galaxy, resulting in the presence of abundant planets. However, it is important to note that the abundance of planets is not necessarily a characteristic exclusively associated with old galaxies in decline.