Scientists made a big mistake. No heat, no light, no energy can radiate into vacuum space. All forms of energy are coexisting with matter/carrier.

Nuclear energy and chemical energy are stored within atoms. Kinetic energy is stored within the motion matters. Thermal energy is carried within matters. Solar energy/radiation is in the sun-facing atmosphere and the sun-facing surface of matters. Electric energy is stored in matters. Gravity is within masses. Magnetic force is within magnets.

Energy must be coexisting with the matter. Force must be coexisting with the matter. Simple nature law and fact.

It is important to realize that in physics today, we have no knowledge of what energy is. We do not have a picture that energy comes in little blobs of a definite amount. It is not that way. -Feynman

All energy is the electrostatic force within matters of working. All energy is from atom formation. The more atoms/mass attracted together by gravity, the denser energy, and higher temperature. 

All planets and stars have a hotter core due to its density is higher. The sun is not a fusion reactor, but a heat sink to keep the earth's temperature stable. The sun will never burn out, the sun is a perpetual alternating electricity generator, a macro atom in fact.