What is a galaxy?

A galaxy is best described as a collection of stars, stellar remnants, and interstellar matter. This definition encompasses the vast variety of structures that constitute a galaxy, which can include billions or even trillions of stars, along with gas, dust, and dark matter. These components interact gravitationally, forming the complex systems we observe in the universe.

Understanding the nature of a galaxy requires recognizing that it's not merely a grouping of celestial bodies but rather a dynamic environment where stars are born, evolve, and sometimes die. The interstellar matter plays a crucial role in star formation, and the stellar remnants include white dwarfs, neutron stars, and black holes, all contributing to the galaxy's overall structure and evolution.

The other options do not adequately capture the essence of what a galaxy is. For example, describing it as a large group of planets orbiting a star focuses too narrowly on a specific type of celestial arrangement, ignoring the broader and more diverse components. A cluster of asteroids suggests a much smaller and less complex arrangement, while a formation of dust and gas lacks the critical aspect of the stars and stellar remnants that define a galaxy. Therefore, the definition that encompasses stars, remnants, and interstellar matter is the most accurate and comprehensive understanding of what