* Dense and massive: The clouds need to be dense enough to overcome the outward pressure of gas and allow gravitational collapse. They also need to be massive enough to retain the gas during collapse, leading to rapid star formation and a spheroidal shape.
* Hot and turbulent: The high temperature and turbulence within the cloud result in a less ordered rotation and more chaotic star formation, contributing to the elliptical shape.
* Possibly with little angular momentum: While not definitively proven, some theories suggest that protogalactic clouds with lower angular momentum are more likely to form elliptical galaxies. This would result in a less organized collapse and less disk-like structure.
Here are some explanations for the characteristics:
* Density and mass: These factors are crucial for gravitational collapse and star formation. If the cloud is not dense enough, it will disperse instead of collapsing. If it's not massive enough, it might not retain the gas during collapse, leading to a less concentrated galaxy.
* Hot and turbulent: This condition leads to a less organized collapse, with stars forming in a more random and less ordered fashion. The lack of a well-defined plane of rotation contributes to the elliptical shape.
* Lower angular momentum: A lower angular momentum allows the cloud to collapse more radially inward, leading to a more spherical shape instead of a flat disk. This is still a subject of ongoing research, and other factors may be involved.
In contrast to the above, spiral galaxies are thought to form from protogalactic clouds that are:
* Less dense and massive: They still need to be massive enough to collapse, but less dense than elliptical protogalactic clouds.
* Cooler and less turbulent: This allows for a more orderly collapse and the formation of a disk.
* With significant angular momentum: This leads to a rotating disk, which is crucial for the formation of spiral arms.
Remember that these are just theoretical models and more research is needed to fully understand how galaxies form. However, the characteristics described above provide a good starting point for understanding the differences between protogalactic clouds that give rise to elliptical and spiral galaxies.
