One model of galaxy formation occurs when sections of gas clouds collapse into small pieces and then merge into larger pieces due to gravity. The Milky Way is an example of the _____ model or the ______ model.
inside-out
outside-in
bottom-up
top-down
bottom-up
The Milky Way is an example of the "bottom-up" model or the "hierarchical" model of galaxy formation. In this model, sections of gas clouds collapse into small pieces, which then merge and accrete over time due to gravity, eventually forming larger structures like galaxies.
The Milky Way is an example of the inside-out model or the top-down model of galaxy formation.
To understand this, we need to break down the options:
1. Inside-out: This model suggests that galaxy formation starts from the central regions and then gradually extends outward. In this scenario, the central bulge and older stars are formed first, followed by the formation of the disk and younger stars. The Milky Way fits this model because it has a prominent central bulge and a flattened disk with younger stars located further out.
2. Outside-in: This model proposes that galaxy formation starts from the outer regions and moves inward. However, observations of the Milky Way do not align with this model as our galaxy exhibits characteristics of inside-out formation.
3. Bottom-up: This model suggests that small structures, such as dwarf galaxies or star clusters, form first, and then gradually merge and assemble to form larger galaxies. While this model may explain the formation of some galaxies, it is not specifically applicable to the Milky Way.
4. Top-down: This model proposes that large-scale structures, such as filaments or dark matter halos, collapse and fragment into smaller pieces which eventually form galaxies. The Milky Way fits this model because it is thought to have formed from the collapse and fragmentation of a vast cloud of gas and dark matter.
Therefore, the Milky Way is an example of the inside-out model or the top-down model of galaxy formation.