Study on the Relationships between Two Gravitationally-bound Points in Single or Multiple Systems in the Universe

Traditionally, Newton's laws are directly used to establish the gravitational relationship between two
objects with any type of motion. However, the relationship is mathematically a vector (or vectors), and
it is difficult to solve, especially when the number of objects is greater than 3, the physical relationship
between objects cannot be simply / clearly revealed. It is even more difficult to study the properties of
a gravitational field. With real data verification error less than 3.5%, we found / proved that physical
properties of the ideal circular motion in the gravitational field are essential / can truly reflect the laws
of motion of gravitationally-bound points in the universe. Regardless the mass of the orbiting point /
body, the central mass and its variation determine the physical properties. In this article, we derive,
use real data to verify and discuss the statistic (fixed central mass systems) expressions / properties
of gravitationally-bound points in single or multiple systems in the universe. Strictly speaking, a star
system like our solar system is a variable central mass system. However, since the rate of solar mass
loss is about 1E-12/year, it can be considered as both a fixed central mass system and a variable
central mass system.