Spiral galaxies are indeed more common than elliptical galaxies in the universe. There are several reasons for this:
Formation from disk instabilities: Spiral galaxies are thought to form through the process of disk instabilities in the early universe. As gas and dust collapse under the influence of gravity, they can develop spiral arms. These arms are regions of enhanced star formation and can eventually evolve into spiral galaxies. On the other hand, elliptical galaxies are believed to form through mergers and interactions between galaxies, which are less frequent events.
Merging and evolution: Over time, galaxies can undergo mergers with other galaxies. When two spiral galaxies collide, they can combine to form an elliptical galaxy. This means that spiral galaxies have the potential to transform into elliptical galaxies, which may explain why ellipticals are less common overall.
Stellar populations: Spiral galaxies are known for their ongoing star formation and possess a mix of young and old stars. They often have prominent spiral arms, where new stars are continuously being formed. In contrast, elliptical galaxies are dominated by older, redder stars and have relatively little ongoing star formation. This indicates that spiral galaxies are more likely to be actively forming new stars, contributing to their higher abundance.
Environment: The environment in which galaxies reside can also play a role. Spiral galaxies tend to be found in less dense regions of the universe, such as galaxy clusters' outskirts, while elliptical galaxies are more commonly located in dense cluster environments. This suggests that the specific conditions and interactions in dense environments favor the formation and evolution of elliptical galaxies.
It's important to note that these explanations are based on current scientific understanding, but our knowledge of galaxy formation and evolution is still evolving. Further observations and research are continually refining our understanding of the factors that contribute to the prevalence of different galaxy types.