What is right ? Energy produced by the sun only comes from nuclear fusion reactions?

There may still be a tiny portion still produced by gravitational contraction and/or loss of gravitational potential as denser elements sink towards the core, but after 5 billion year and will all the convection going on, I would expect that this is an extremely small fraction that can be safely ignored in the type of calculations we do on Yahoo!Answers. Still, the value is not completely zero as there is still "stuff" falling onto the Sun (we can certainly see the occasional comet, and there must be the occasional asteroid).

There may also be an almost-as-tiny fraction being produced by tidal braking (mostly due to Jupiter and Saturn). Again, other than the mathematical curiosity, this can be ignored.

in reality the gravity and warm temperature from the daylight reason hydrogen atoms to fuse into helium atoms. also some helium atoms fuse with different helium or hydrogen to make different aspects too. at the same time as this fusion takes position power is released, interior the shape of electrons. it is honestly a very small volume of power in holding with reaction, yet there are trillions taking position each and every 2d, so the quantity of power is great.

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1. The sun has produced energy for 4-5 billion years (or time of 9-12 billion years, God knows better than us)

2. Multiply 700 million tons of hydrogen "consumed" per second by the Sun with the number of seconds of 4-5 billion years.That, the Sun, at the beginning, had a diameter larger than our galaxy.

3. It implies the existence of a "Black Hole" in the solid core of the Sun, and unknown reactions of primary particles ( similitude = primary particles appeared after the Big Bang)

4. Relativity Existence together matter-anti-matter, would explain the realization of astronomical energies by the Sun, and a reasonable size, to the beginning of its formation.

The present concept of solar heat & consistent energy release shows the Bohr - Born cycle is responsible for all what we get, or rather record.Only H2& He are present in solar spectra in measurable quantities- this indirectly proves our concept. So till we get another concept & proof, H---> D----> He transformation [fusion] only is main source of solar energy.

As there is no oxygen on the surface of sun therefore, no combustion takes place. Thus the nuclear reactions are the only source of energy of sun.

It also comes from Gravitational Contraction,but for for the most part,it is nuclear fusion.