Binding energy is the term used to specify the amount of energy necessary to hold components of a system together, usually in describing the interactions within constituents of molecular, atomic or nuclear systems. However, it can also be used in describing astrophysical systems. Through binding energy, the system is relatively stable and allowed to act as a unit. The measure of the energy necessary to hold a system together is essentially equal to amount of energy necessary to break the system apart. Therefore "binding energy" is used in reference to both processes.

At the astrophysical level, the force of gravity provides much of the binding energy necessary to keep solar systems as units. Gravity holds the components of a system together because no matter how small the system's "particle" (Newton's term) is, it will have an attraction to another object proportional to the mass of the...