NSES Content Standard D  Earth and Space Science: Origin and evolution of the universe Grades 9-12, page 190 Stars produce energy from nuclear reactions, primarily the fusion of hydrogen to form helium. These and other processes in stars have lead to the formation of all the other elements.

 
Benchmark 4A The Physical Setting: The Universe
Grades 9-12, page 65
On the basis of scientific evidence, the universe is estimated to be over ten billion years old. The current theory is that its entire contents expanded explosively from a hot, dense, chaotic mass. Stars condensed by gravity out of clouds of molecules of the lightest elements until nuclear fusion of the light elements into heavier ones began to occur. Fusion released great amounts of energy over millions of years. Eventually, some stars exploded, producing clouds of heavy elements from which other stars and planets could later condense. The process of star formation and destruction continues.

Benchmark 4G The Physical Setting: Forces of Nature
Grades 9-12, page 97
The forces that hold the nucleus of an atom together are much stronger than the electromagnetic force. That is why such great amounts of energy are released from the nuclear reactions in the sun and other stars.