1. Galaxies Can Grow Over Time
The current size of a galaxy is not limited to the size it had when it formed. Galaxies influence the matter around them through their gravity and can interact with other galaxies over time. Especially around large galaxies, there may be much smaller satellite galaxies.
Some of these small galaxies may gradually approach the gravitational field of the larger galaxy and eventually merge with it. In this way, the large galaxy gains new contributions of stars, gas, and dark matter.
2. Why Are Dwarf Galaxies Important?
Dwarf galaxies are much smaller star systems compared to large galaxies. Although their sizes and masses are much lower than those of large galaxies, their numbers can be quite high.
These small systems around a large galaxy can remain in orbit for a long time. However, due to gravitational interactions, their orbits may change and some may be drawn toward the main galaxy.
3. Gravity That Initiates the Merger
When two galaxies approach each other, the gravitational interaction between them intensifies. As the small galaxy's motion is affected by the gravitational field of the large galaxy, the large galaxy is also influenced by the mass distribution of the smaller system.
During the approach, the shapes of the galaxies may become distorted. Especially the large structures formed by stars and gas can be stretched, and the galaxy's previously regular appearance may begin to change.
4. How Does Galaxy Cannibalism Occur?
The process of a large galaxy absorbing a smaller one over time is sometimes described as galactic cannibalism. The stars and other matter of the small galaxy are redistributed within the gravitational field of the larger system.
When the merger is complete, the original integrity of the small galaxy may disappear. Its stars mix into the large galaxy's vast stellar population, while some may form long and sparse streams in the outer regions of the galaxy.
5. Why Don’t Stars Collide?
Although the merging of galaxies is a huge event, collisions between individual stars are extremely rare. The main reason is that the distances between stars are incredibly large compared to the sizes of the stars themselves.
Therefore, the merging of two galaxies is not like the collision of two solid objects. The orbits of the stars change due to gravity, and the overall structure of the galaxy is rearranged.
6. Gas Clouds Behave Differently
The gas and dust in galaxies, unlike stars, can collide and compress. When two galaxies approach each other, their gas clouds can intermingle and condense due to gravitational movements.
This condensation can accelerate the formation of new stars. Thus, a galaxy merger not only causes existing stars to change places but can also lead to the birth of new stars.
7. The Shape of the Galaxy Can Change
The merging of galaxies can have strong effects, especially on spiral structures. The order of spiral arms can be disrupted, the orbits of stars can change, and tidal tails extending into the outer regions of the galaxy may appear.
The collisions of galaxies and the formation of such structures are among the important processes studied alongside the growth of galaxies.
8. Star Formation During the Merger
The compression of gas can cause star formation in merging galaxies to occur faster than normal. Especially when two gas-rich galaxies interact, it is possible for a large number of new stars to form within relatively short cosmic timescales.
These new stars can affect the later appearance of the galaxy. Thus, a merger not only changes the current structure of the galaxy but also shapes its future stellar population.
9. The Small Galaxy May Disappear Completely
When a dwarf galaxy merges with a large galaxy, it does not necessarily retain its former shape. The stars of the small system may disperse among the stars of the large galaxy, and over time it may become difficult to distinguish the original galaxy as a separate structure.
However, the history of the small galaxy does not have to be completely erased. Stellar streams, chemical properties, and irregularities in the outer regions of the galaxy can carry traces of past mergers.
10. A Continuous Growth Process for Large Galaxies
The merger of a single dwarf galaxy may not dramatically change the total size of a large galaxy. However, when many small mergers accumulate over a long time, significant growth can occur.
Therefore, instead of explaining the growth of galaxies with a single giant collision, it should be considered as the result of small and large mergers coming together over long cosmic timescales. In the source, the "growth" and "collisions" of galaxies are discussed under separate headings.
11. The Role of Dark Matter
Understanding that galaxies are not made up of only stars is also important for explaining merger processes. Galaxies have extensive dark matter halos around them, and the gravitational effect of these structures determines the movements of galaxies.
Therefore, the approach of a dwarf galaxy to a large galaxy is not just about the movement of visible stars. The broad mass distributions of the two systems affect each other and are among the key factors that determine the timing and nature of the merger.
12. Mergers Are Part of Galaxy Evolution
The fact that galaxies have different shapes and sizes shows that their histories can also be different from each other. Some may have undergone a more tranquil evolution, while others may have experienced many interactions.
While the source discusses different types of galaxies such as spiral, elliptical, irregular, and barred spiral separately, the growth and collisions of galaxies are also presented as parts of galaxy evolution.
13. Traces of Mergers Can Be Seen Today
Astronomers can observe long and thin stellar streams around some galaxies that differ from the structure of a normal galaxy. Such structures may be remnants of a galaxy interaction that occurred in the past.
Especially during the disruption of a small galaxy by a large one, not all stars remain in the same place. Some are scattered along long orbits around the main galaxy and can preserve traces of past mergers.
14. The Milky Way Is Not Exempt from This Process
There are many small satellite galaxies around the Milky Way. Some of these interact strongly with the Milky Way's gravitational field.
This shows that large galaxies are in a constant gravitational relationship with the small galaxies around them. Therefore, the growth of galaxies is not just a distant and past event, but a natural part of the long-term evolution of galaxies.
15. Conclusion and Evaluation
The growth of large galaxies by merging with dwarf galaxies is one of the important pathways of galactic evolution in the universe. Gravity can draw small galaxies toward large systems over time; during the merger, the orbits of stars can change, gas can compress, and new star formation can accelerate.
Even if the separate identity of the small galaxy disappears when this process is complete, traces of past mergers can remain in stellar streams, in the outer regions of the galaxy, and in the properties of the stellar population. Thus, the large galaxies we see today become gigantic systems that bear the cosmic traces of numerous mergers in their past.