The model you're referring to is known as Hierarchical Galaxy Formation. This model posits that smaller structures, such as protogalaxies or globular clusters, form first and then merge together due to gravitational attraction, leading to the formation of larger galaxies over time.
Key Aspects of Hierarchical Galaxy Formation:
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Small to Large: Initially, massive dark matter halos form from small density fluctuations in the early universe. These halos can contain gas and dark matter, serving as the building blocks for galaxies.
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Mergers and Accretion: As these small structures evolve, they can merge with each other, leading to larger entities. This process is often driven by gravitational interactions and can be observed in simulations of cosmic structure formation.
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Role of Dark Matter: Dark matter plays a crucial role in this model as it provides the gravitational backdrop necessary for smaller halos to merge and form larger ones. The presence of dark matter enhances the gravitational pull, allowing these smaller structures to combine effectively.
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Star Formation: During the merging process, gas within the merging structures can collapse to form stars, often leading to bursts of star formation. This is seen in galaxy mergers, where gas is funneled towards the center of merging galaxies, resulting in intense starburst activity.
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Evolution Over Time: Over billions of years, this hierarchical process leads to the formation of large galaxies, including spiral, elliptical, and irregular galaxies. Simulations based on this model effectively reproduce many observed phenomena, including the distribution of galaxy masses and sizes.
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Comparison with Monolithic Collapse: Hierarchical formation contrasts with the monolithic collapse model, which suggests that a galaxy forms from a single, rapidly collapsing gaseous cloud. The hierarchical model is better supported by observational evidence and simulations of cosmic evolution.
Observational Evidence:
The discovery of distant galaxies and observations of their structures have supported hierarchical formation. The prevalence of galaxy clusters and groups, along with phenomena such as galaxy mergers observed in various stages, bolsters this model.
In summary, hierarchical galaxy formation provides a comprehensive framework for understanding the complex processes that led to the structure of galaxies we observe today in the universe.
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