Much about the nature of dark energy is still theoretical or unknown. Cosmologists developed the idea of dark energy to answer the question of why the universe is expanding at an increasing rate. Some dark matter theorists believe that it is a force that operates opposite to the way gravity acts, pushing outward at an expanding rate. Alternately, dark energy could be a quality that exists naturally as a part of space. Other theorists speculate that dark energy is a new energy field. Cosmologists continue debating the nature of dark energy, but currently they believe that it is the force that is increasing the rate of cosmic expansion.
Nuclear energy is the primary sustaining force in all stars. Nuclear fusion, occurring at the center of stars as plasma hydrogen atoms combine to form helium atoms, releases the light energy that you see when you look at a star and the heat energy that you feel from the sun. The gravity in the center of a star creates the necessary friction to perpetuate the process, sustaining a consistent release of energy in the form of light.
Kinetic energy is the energy that an object possesses as a result of its motion. Kinetic energy can be leftover energy from the Big Bang or energy gained from the expense of potential energy. Planetary bodies possess significant kinetic energy that is used, with potential energy, to establish orbits around other cosmic bodies, such as the orbit of planets around stars or moons around planets.
Potential energy is the energy that exists within an object from its position relative to another, internal energy forces, electric charges or other contributing factors. Potential energy exists when a force pulls an object towards a specific destination but it is not allowed to move towards its destination, such as when you hold a rock in the air and the gravity of the earth is pulling down on the rock. In the universe, potential energy exists as a counterpoint to kinetic energy, pulling planets towards local stars. The connection between kinetic energy and potential energy establishes the orbits of planets, while keeping them from propelling themselves into stars.