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Physics Girl: Super-Kamiokande – Imaging the sun by detecting neutrinos [video]

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Re: Physics Girl: Super-Kamiokande – Imaging the sun by detecting neutrinos [video]

#41

Post by Hikikomori »

gosub100 wrote: post #32
Brajeshwar wrote: post #3

Welcome back. One of my staple YouTube Subscriptions. I’m today years old learning that the light that we actually see on earth today came out 100s of thousands of years ago.

It's not the same photon though. The fusion happens in the core, then takes millennia for the energy to escape. During that time photons are emitted and absorbed by the atoms, until the surface emits one that finally travels to the earth in 8 minutes. Anyway that's taking you from the ELI5 to the ELI9 version. I'm sure someone on here can correct it further.

Similar to how infrared radiation works in our atmosphere, minus the timescale?

Re: Physics Girl: Super-Kamiokande – Imaging the sun by detecting neutrinos [video]

#44

Post by gus_massa »

amluto wrote: post #34
gosub100 wrote: post #32

Earlier quoted context omitted.

It's not the same photon though. The fusion happens in the core, then takes millennia for the energy to escape. During that time photons are emitted and absorbed by the atoms, until the surface emits one that finally travels to the earth in 8 minutes. Anyway that's taking you from the ELI5 to the ELI9 version. I'm sure someone on here can correct it further.

I haven’t tried to look up the history of this claim, but here are some guesses: 1. There’s a sort of diffusion process going on. Photons from the core have some mean free path as a function of radial position (and, obnoxiously, of wavelength as well, so maybe we ignore that). You could calculate the mean time for a hypothetical object emitted from the core and traveling according to those mean free paths to escape.…

I agree. I read the 5000 years time a few times and I don't like it.

When you have a transparent medium like water or glass, the photon that enters and the photon that exit share a lot of properties, in particular energy/color/frequency. Perhaps they have a shift in the phase or a different polarization (like in water with sugar or if you want to be fancy a quarter wave plate). You can still split a beam before in enter and make interference experiments after half of it passed though water or glass, and other weird experiments, so I think it's fair to call them "the same photon".

But in the Sun, the original photons in the center of the Sun have a few very specific values of energy/color/frequency, that are totally lost. (But the neutrinos have so few interactions that they don't lose this information, and it's possible to do neutrino spectroscopy!)

Also, the photons emitted by the "surface" of the Sun have a wide spectrum of energy/color/frequency that is very close to black body radiation at something like 5000K-6000K.

So in my opinion it's better to think that the original photon in the center is absorbed shortly after it's emitted, and transformed into heat. The heat takes 5000 years to get to the surface. And then the hot surface emits a few new photons unrelated to the original one.

I'm not sure what is the main transmission method inside the Sun: conduction, convection or radiation.

Re: Physics Girl: Super-Kamiokande – Imaging the sun by detecting neutrinos [video]

#46

Post by mikkupikku »

pantulis wrote: post #24
MyHonestOpinon wrote: post #16

Earlier quoted context omitted.

Oh, probably skipped physics too. I haven't seen the video (yet), but I would have bet that light on earth came out 8 minutes ago from the sun.

Light from the sun that is reaching us now escaped the surface of the sun 8 minutes ago, yes. But photons are generated in the core through nuclear reactions, where they take their sweet amount of thousands of years bouncing around until they get out.

I think this is right in a certain sense, but not precisely. From what I understand no visible light photons are created in the core from nuclear fusion, it's mostly a bunch of gamma rays that get almost immediately absorbed. The energy, but not the photons from fusion, gets transfered up through the layers of the sun, through radiation and convection, eventually heating the photosphere. It is then the photosphere, white hot, which ultimately radiates the visible light we see as sunlight.

Re: Physics Girl: Super-Kamiokande – Imaging the sun by detecting neutrinos [video]

#47

Post by shadowgovt »

One of my favorite bits of astrophysics trivia is that the neutrino detection experiments serve as an early-warning system for supernovae, to allow astronomers to prioritize telescope time and swing the scopes around to see the first visible-light and radio signals of the event.

This is because the electromagnetic energy of the supernova can take hours to force its way through all the star's mass to the surface when the core dies, but the gravitational crush turning protons and electrons into neutrons releases a massive burst of neutrinos in every direction. And the neutrinos are so weakly-interacting with the matter in the star that they get out first. Then, a million years later, arrive in our solar system at such a high fraction of lightspeed that they presage the coming electromagnetic shock-front because the constant difference in escape time between neturinos, which are particles of matter, getting out of the star without interacting with anything and the electromagnetic waves moving through the star's matter at a fraction of lightspeed created a gap that the light never caught up to.

The universe is a profoundly wild place.

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