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Comment by margalabargala | Hacker News Reader

> therefore an average density of 5.33 to 8.38 mg/m3

That's nuts. How on earth does fusion happen at that density? Is there a denser core that actually fuses, and the outer fluffy bits just glow from the inner heat?

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Averages are quite misleading. The core is obviously a lot denser. Our sun has an average energy output per cubic meter that is comparable to a compost heap.

Sure, but now I'm left wondering what the size of the body doing fusion is. If most of the star is glorified glowing atmosphere, I want to know the mass and radius of the fusing bits.

There's dedicated Wikipedia articles responsive to this,

https://en.wikipedia.org/wiki/Solar_core

Depends on the class of the star. Our sun? About 1/4 radius and in is fusion reaction. But it gets weird in other stars. In red giants the fusion zone is a very small shell around a dead core. Maybe something like earths orbit in radius, but very very thin.

Astra says this claim is misleading. Sun's average energy output per cubic meter is three orders of magnitude smaller than that of a compost heap. The fusion core is comparable though.

The energy density of specific compost heaps varies by several orders of magnitude it’s not a single number. Volume, moisture content, internal temperature, external temperature, materials being composted, etc all play a significant role.

Stellar fusion could also be a factor in a sufficiently large compost heap.

Of course it's misleading, thats the point GP was trying to make. Averages belie truth in large, diverse systems with extremes

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