What is the structure of galaxies?

The structure of galaxies and the universe at large can be quite complex. Here's a concise summary based on insights from astrophysicist Neil deGrasse Tyson:

• Galaxy Formation: On a small scale, gravity tends to form spheres and disks. However, on a larger scale, galaxies do not evenly spread out. Instead, they form web-like or spongy structures.
• Cluster Shapes: Some galaxy clusters, like the Coma cluster, are nearly spherical and were crucial in the discovery of dark matter. Calculations revealed that the gravitational mass required to keep these galaxies together is far greater than the visible mass, pointing to the presence of dark matter.
• Filamentary Structures: The large-scale structure of the universe resembles a sponge's cross-section with filaments connecting galaxy clusters. These structures are so vast that the universe isn't old enough for galaxies to have traversed these filaments completely, indicating that these systems are not gravitationally settled.

This complex arrangement highlights ongoing mysteries in astrophysics, such as the dark matter problem, first identified in the 1930s by Fritz Zwicky 1 .