Does anyone know what kind of energy could be found in an isolated body in space, supposing the body is an electron, a planet or a quasar?

Motion is energy.
Kinetic energy is on type that all objects in space possess regardless of their location. Take for example the comets. Notice the tremendous impact that one made when it was gravitationally dismembered by Jupiter. Cosmic rays too have kinetic energy due to their high velocity.

Neither does isolation mean that the body has be cold.
There are rogue stars that wander between galaxies. Many are thought to have been flung out of their orbits due to their binary companion having gone nova or due to the effects of galactice near misses or collisions. Such stars continue to shine via nuclear fusion despite their isolation.

Quasars, or Quasi SDtellar Objects are thought to produce their energies via the black hole that resides at their centers. As matter falles into the black hole it gives off X-rays. That is one tell-tale sign that a black hole is the cause.

Other possible isolated objects, such as Brown Dwarfs or failed stars and white dwarfs or dying stars produce energy via gravitational collapse since there is insufficiet mass to fire the furnaces of nuclear fusion..



Some isolated planets, might produce magnetic energies due to their flowing semi fluid metallic cores at their center. Ths movement is thought to