Dark matter is believed to play a significant role in holding galaxies together through its gravitational influence. While the exact nature of dark matter remains unknown, its gravitational effects can be observed and measured indirectly.
Galaxies consist of various components, including stars, gas, and dust. However, the visible matter alone cannot account for the observed motions and stability of galaxies. According to the gravitational interaction described by Newton's laws, galaxies should not be able to maintain their structure and rotational velocities without additional mass.
Dark matter, which does not interact with light or other electromagnetic forces, provides the missing mass required to explain the observed dynamics. Its gravitational pull counteracts the outward centrifugal forces generated by the visible matter in galaxies, preventing them from flying apart.
One way to understand this is by considering the concept of gravitational potential energy. As visible matter moves within a galaxy, it is subject to the gravitational pull of the dark matter halo surrounding the galaxy. This gravitational potential energy effectively adds an extra "glue" that holds the galaxy together.
Observations of galactic rotation curves provide strong evidence for the presence of dark matter. Rotation curves describe the velocities of stars or gas as a function of their distance from the galactic center. These curves demonstrate that the velocities remain constant or even increase with distance, indicating the presence of additional mass beyond what is accounted for by visible matter.
The distribution of dark matter within galaxies is still a subject of ongoing research and investigation. It is generally thought to form a halo around the galaxy, extending well beyond the visible disk. The exact properties and behavior of dark matter are still being explored through various observational techniques, such as gravitational lensing and simulations.
In summary, dark matter's gravitational influence counterbalances the outward forces in galaxies, helping to hold them together despite the observed motions of visible matter. While its precise nature remains elusive, dark matter's presence is necessary to explain the structure and dynamics of galaxies as we observe them.