I followed a thread here that included the surprising fact that Hydrogen fusion is so unlikely the power output per volume of the core of the sun is only about the same as a compost heap.<p>The reason the sun is so bright and hot is its size.
A pile of compost the size of the Sun would rapidly collapse into a smaller sphere under its own gravity. This would liberate an enormous amount of gravitational potential energy, causing the pile to dissociate into a superhot gas and radiate like a star.<p>The average density of the Sun is 1.4 g/cm^3; the average density of compost is about 1/3rd of that. So this sphere of compost would collapse into an actual star about 1/3rd the mass of the Sun. Its core would be hot enough to sustain nuclear fusion.