The concept of the "end" of the galaxy can be interpreted in different ways, depending on what aspect you're referring to. Here are a few possibilities:
Expansion into space: The Milky Way galaxy, like many other galaxies, is constantly expanding. However, there is no definitive edge or boundary to the galaxy. Instead, the density of stars gradually decreases as you move toward the outskirts. So, in terms of spatial extent, the galaxy doesn't have a clear-cut end.
Galactic rotation: The Milky Way is a spiral galaxy that rotates around its center. The rotation speed varies with distance from the center. The concept of the "end" of the galaxy can refer to the point at which the rotation speed decreases significantly or comes to a halt. However, it's important to note that the galaxy is a dynamic system, and its rotation is complex and influenced by various factors.
Evolution and lifespan: Galaxies, including the Milky Way, have lifespans that span billions of years. Over time, galaxies undergo changes, such as merging with other galaxies or experiencing the depletion of their interstellar gas, which fuels star formation. The "end" of a galaxy, in this context, could refer to the point at which it exhausts its resources or undergoes a significant transformation, potentially leading to the formation of a new type of structure.
The future of the universe: In the far future, billions of years from now, theories suggest that galaxies may become increasingly isolated as the universe expands at an accelerating rate. This could lead to a scenario known as the "cosmic dark age" when the supply of gas and the ability to form new stars diminishes. This could be considered an end for star formation within galaxies, but it doesn't necessarily mean the complete cessation of all galactic activity.
It's important to note that our understanding of the universe is continually evolving, and new discoveries can reshape our knowledge. The concept of the "end" of the galaxy is subject to scientific investigation and interpretation.