Determining whether a galaxy is at the "edge of space" requires understanding a concept known as the observable universe. The observable universe refers to the portion of the universe that we can potentially observe from our vantage point on Earth, given the finite speed of light and the age of the universe.
Scientists estimate the age of the universe to be approximately 13.8 billion years. Since the speed of light is finite, the light from distant objects takes time to reach us. Therefore, the farther we look into space, the further back in time we are observing.
When astronomers observe galaxies, they are essentially looking back in time because the light they detect has traveled across vast distances to reach us. The concept of the observable universe defines the boundary beyond which light has not had sufficient time to reach us since the beginning of the universe.
The current estimate for the radius of the observable universe is about 46.5 billion light-years. However, it's important to note that this doesn't imply that the universe is only 46.5 billion years old. Due to the expansion of space itself, the objects we observe as being close to the edge of the observable universe have actually moved further away from us over time.
To determine if a galaxy is at the edge of the observable universe, scientists consider its redshift. Redshift is a phenomenon in which light from distant objects appears shifted towards longer wavelengths due to the expansion of the universe. The amount of redshift observed can provide an indication of the galaxy's distance and its position relative to the edge of the observable universe.
If a galaxy's redshift indicates that it is at the maximum observable distance, meaning that the light from that galaxy has taken the entire age of the universe to reach us, then it can be considered to be at the "edge of space" as far as our current observations allow.
It's important to note that our understanding of the universe is continually evolving, and future advancements in technology and observations may refine our knowledge of the observable universe and its boundaries.