without matter, there is no energy, no force, nothing. no us, no thought.

matter is made from charged particles.

opposite charged particles attract each other, they collide like magnet and iron ball. the impact force/energy becomes heat/thermal energy of the atoms.

the more atoms get together by gravity attraction, the more mass is added, the higher thermal energy density, the higher temperature.

so bigger star carry more energy, produce stronger light.

the energy is stored in vibrating atoms/charged particles.

the energy a star carry is the vibrating gravity and electrostatic force in its total mass/charges.

the sun's energy is from star formation, the sun is not an active nuclear reactor.

the energy cannot vanish into space but share with other matters surround according to their distance.