# Hierarchy of gravitational interactions of astronomical objects: from single to large-scale structures

Hierarchical structure is clearly visible in the Universe. The "observable universe" includes almost empty voids, between which lie large cosmic filaments. The filaments consist of galactic superclusters, organized from groups and clusters of galaxies of many different sizes and shapes. Depending on the galaxy's morphological type, a galaxy may have several structural components, including spiral arms, a halo, and a core. Galaxies can have satellites in the form of dwarf galaxies and globular star clusters. The constituent parts of galaxies, star clusters, and other smaller star systems (orbiting each other or a center of mass) are formed from stars. Planetary systems and small bodies such as asteroids, comets and objects in fragment disks are formed by accretion processes in the protoplanetary disk surrounding newborn stars.

If we depict this hierarchy very roughly and very schematically, it will look as shown in the figure (small bodies revolve around satellites, satellites around planets, planets around stars, etc.).

What determines the existence of this hierarchy and why on cosmological scales does rotational motion turn into translational motion towards the great attractor? I assume that the gravitational field on a wide range of scales (from planetary to cosmological) has many minima of gravitational potential. Potential minima are the most favorable state of the field, since in them the field energy is minimal. Thus, the gravitational field on a wide range of scales (from planetary to cosmological) has more than one ground state (that is, the state with minimum energy).

No, gravitation has, as far as we know it, the same form on all scales. There is some nonlinearity when gravitation gets very strong due to general relativity, but this is not relevant for the hierarchy in this question. A system with bodies of masses $$m_1, m_2, m_3, \ldots$$ behaves the same as a system where you scale the masses to $$sm_1, sm_2, sm_3, \ldots$$ and rescale all distances by $$s$$. So it is not strange that systems on very different scales behave roughly the same.