Surprising fact about the sun: it actually produces less heat per unit volume than a compost pile - this makes sense when you consider that fusion events are very rare.
The reason the sun is so hot is that it has an enormous ratio of volume to surface area. Heat emission due to radiative cooling is proportional to the surface area, but heat creation due to fusion is proportional to the volume.
The density of the Sun isn't uniform of course, but according to this[0] StackExchange answer, the density of matter in the Sun already reaches that of air at about 95% of its radius.
Life requires a stable environment in which persistent structures can be maintained over long periods of time. High temperatures are inimical to that. This is why we live in a part of the universe where temperatures rarely rise much above a few hundred degrees Kelvin. Above that most complex chemical structures break down.
Even more fundamentally, a life form needs to be able to pump entropy out more quickly than it comes in, no matter what its substrate is. With all that heat and light and magnetic fields running around and pressing in on any conceivable life form living in the sun, there's no way it could possibly pump it out fast enough.
With that analysis you don't have to get into the weeds of what exactly plasma and magnetic fields might theoretically be able to cohere into and whether it may be able to be life someday... it doesn't matter. There's no way sun life can pump out the entropy fast enough no matter what.
(On the flip side, one can imagine some form of nebula, gas-cloud life, but they would have to be so slow that there's no chance any of it could evolve into anything terribly complicated in the life time of the universe. If we ever did find some it would double as proof that there must have been some other life form that created it.)
This is true only on its surface. Most fusion energy production happens in Sun's core and that stuff is both more dense and produces much more energy per unit volume than a compost pile.
I mean, yeah. But at some point the pile will become large enough to collapse in on itself from gravity and start fusion, I would imagine.
So, according to Cornell[don't know how to do a citation], "1,000 BTU per hour per ton" is a good heat capture rate from manure compost. Then, according to something called 'alternative energy geek' "the earth receives 82 million quads of Btu energy from the sun each year. A "quad" is one quadrillion British Thermal Units (BTUs) of energy."
So, to recreate that, we would need. Um. One massive shitload of compost to recreate that.
The reason the sun is so hot is that it has an enormous ratio of volume to surface area. Heat emission due to radiative cooling is proportional to the surface area, but heat creation due to fusion is proportional to the volume.