How does the sun produce photons?

05 June 2011



I was wondering, how are photons created in the sun, and how do they get propelled at the speed of light towards the Earth? With great thanks,
Hong Shee


Dominic - The surface of the Sun is very hot of course. It's so hot that hydrogen becomes ionised into plasma so that you have protons and electrons as separate bodies, rather than bound together into atoms. As those different charges interact, they can lose energy which is radiated as the photons that we see. Now that's not actually the powerhouse that drives luminosity of the Sun. That is the fusion of hydrogen atoms into helium which occurs at the core of the Sun - in fact, only in the central 20% or so of the Sun; you have another process, which is convection, which is carrying that heat generated at the centre of the sun out to the surface to keep the surface hot so that it continues to shine.

Chris - Are there no photons being produced deep inside the Sun? Presumably there are, but they just can't get out.

Dominic - Yes. Photons are being produced all throughout the Sun; but the Sun is made of a cloudy material because the protons and electrons inside the Sun can interact with those photons. And that means the photons produced deep down can only actually travel a few centimetres before they're reabsorbed.

Chris - Brian Fulton, professor of Astrophysics at the University of York, when he was on this programme he made the point that the photons that get made in the Sun are actually a million years old plus by the time they emerge because they have spent their entire life being bombarded around and absorbed and reabsorbed, ad infinitum almost before they finally escape. So, if the Sun went out tomorrow - as in all reactions stopped - we'd still have a million years of the light locked inside.

Dominic - That's absolutely right. The light is travelling at the speed of light, but it's only hopping a few centimetres at a time and we don't know what direction it's going to come back out again. It may end up going back towards the centre of the Sun again and it takes a million years to get out. It's quite a random walk for that energy to get to the surface.


what do scientists call a photons journey to the suns surface?

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