How are the bars in barred spiral galaxies thought to have formed?(1 point) Responses slow evolution slow evolution primordial collapse primordial collapse merging merging separation
The bars in barred spiral galaxies are thought to have formed through a process called slow evolution.
The bars in barred spiral galaxies are thought to have formed through a process called "primordial collapse." This refers to the initial collapse of gas and dust in the early stages of galaxy formation, which led to the formation of a central bar structure. This collapse occurs due to the gravitational forces acting on the material, causing it to condense and form a rotating disk-shaped structure. Over time, as the galaxy evolves, other processes such as merging and separation may also play a role in shaping and modifying the bar structure. However, the primary mechanism for the formation of bars is believed to be the primordial collapse during galaxy formation.
The formation of bars in barred spiral galaxies is thought to occur through a process called "secular evolution." This process involves the slow evolution of a galaxy's structure over a long period of time.
To understand how bars form, let's go over the steps involved:
1. Initially, a spiral galaxy has a central bulge surrounded by a disk of stars and gas. The disk consists of spiral arms which sometimes extend across the entire disk.
2. As the galaxy rotates, different regions of the disk experience varying gravitational forces. This causes shear and compression in the gas and stars of the disk.
3. Over time, these shear forces and interactions between stars lead to the formation of elongated orbits that are aligned with the direction of rotation.
4. As more stars adopt these elongated orbits, a central bar structure begins to form. This bar can extend for several kiloparsecs across the galaxy's central region.
5. The formation of a bar triggers changes in the dynamics of the galaxy. It can enhance the inflow of gas towards the center, potentially fueling the formation of new stars.
6. Additionally, the bar can create regions of high star formation known as "starbursts" along the leading edges of the bar.
It is important to note that barred spiral galaxies are believed to have undergone a combination of processes, including slow evolution, primordial collapse, merging, and separation. However, the formation of bars specifically is primarily attributed to the slow evolution of the galaxy's structure over time.