Experimental status of stellar structure

[muppet]

A naive question from someone who knows nothing about the subject:

I was wondering how much we can tell experimentally about what's going on inside a star. Can we determine, say, how the temperature or pressure vary as a function of the radius?

Thanks in advance.

 

[Drakkith]

Not purely by experiments, no. But we know a great deal about the basics of physics and can build models that predict what the internal structure should be like. We can then take our observations from experiments we CAN do and compare them to predictions by our models. If they match, then we take that to mean our models are accurate.

 

[muppet]

Thanks for your reply. Can I ask you to elaborate about what we can predict and test, based on such models?

 

[Drakkith]

Sure. For example, we know how pressure and heat builds as you compress a gas. Knowing the mass of the Sun and the radius we can predict what the temperature inside the Sun should be. If our prediction is accurate, the core should approach a temperature that allows it to fuse protons together to form helium. So how do we know that the Sun is fusing hydrogen? Well, one way is that we know the fusion process releases particles known as neutrinos. Neutrinos don't interact very well with matter and can pass through the Sun very easily. We have detectors here on Earth that have detected a small portion of these neutrinos, giving us evidence that the Sun is indeed fusing hydrogen in its core.

Does that make sense?

 

[muppet]

Sure, thanks. [Just to clarify, I know a bit about general physics, just not astrophysics! My undergrad degree was in maths and physics, so astrophysics was the sort of thing that had to make way for the maths...]