Why is the sun able to undergo fusion so easily, compared to us?

Question

I’ve read maybe it has something to do with gravity…? But we have gravity here on earth too.

And while the sun’s internal temperature is around 15M degrees celsius, apparently for us to replicate the fusion effect here on Earth, we need to superheat atoms to 100M degrees celsius. Why the difference?

In: 11

Answer 1

Short answer: the sun is goddamned huge.

> And while the sun’s internal temperature is around 15M degrees celsius, apparently for us to replicate the fusion effect here on Earth, we need to superheat atoms to 100M degrees celsius. Why the difference?

Two reasons. First, the Sun’s core is under [incredible pressure](https://en.wikipedia.org/wiki/Solar_core), a million times higher than the [highest pressures we can achieve](https://gsecars.uchicago.edu/scientific-program/high-pressure-high-temperature-large-volume-press/) for a large volume of material in the lab. This mashes the atoms together real good and makes fusion more likely.

Second, even with the high pressure and temperature, fusion in the sun is really slow. Power output in the core is about [300 watts per cubic meter](https://en.wikipedia.org/wiki/Solar_core). This is far less than the heat density generated by the human body or a compost heap. You’d need a volume of superhot superdense plasma bigger than a football stadium just to power a small city. … and even then it wouldn’t work because all the heat would leak out the side walls of the football stadium.

So if the sun’s power density is so weak, how can it light up the whole solar system? See above: the sun is goddamned huge. Like, no matter how big you think the sun is, it’s bigger than that.

On Earth, if we want fusion to be a practical energy source, we need to fuse hydrogen atoms in a more compact way than the goddamned huge sun does. Which means we need higher power density, and hotter temperatures, than the sun.