What is the upper limit of interstellar space?

The upper limit of interstellar space is defined as the point between solar systems. This is because interstellar space refers to the region of space that exists between stars within a galaxy, and it is characterized by very low density and pressure compared to areas within a solar system or a galaxy.

When considering the space between solar systems, it is essential to recognize that this region extends beyond the influence of any single star or planetary system's gravity. The interstellar medium, which is primarily made up of gas and dust, fills this vast distance, creating an area that is distinctly different from both the solar system, where celestial bodies are bound by gravitational forces to a star, and the broader structure of a galaxy.

Other options do not accurately convey the specific boundary of interstellar space. For example, the edge of our galaxy refers to the limit of the Milky Way galaxy’s diameter, which incorporates many solar systems and does not define the transition to interstellar space. The distance at which stars begin to appear is subjective and can vary greatly depending on the observational capabilities, and it does not specify a clear boundary. Meanwhile, the boundary of our solar system denotes the furthest extent of the Sun's gravitational influence, known as the heliopause, which is not