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We know from the sun, we receive x-rays, gamma-rays but at a very small number of photons.

Question 1: why not much ? is it because most of the x-rays are absorbed in a process of ionization of the atoms in the outer layer of the sun ? If so, some x-ray photons still leave the sun. Is it because at some low probability, from the core, these x-rays didn't collide with anything and got very lucky ?

Question 2: In the sun process, outer layer, where ionized plasma is, we know Bremsstrahlung takes place. can Bremsstrahlung in there produce x-rays as well ? we know it has continous spectrum, so i guess it can. Wouldn't these x-rays produced there leave the sun towards us ? This logic kind of makes me believe that there should be more x-rays leaving the sun than at the spectrum we see.

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  • $\begingroup$ Giorgi - please focus your posts on just 1 question. $\endgroup$
    – Rory Alsop
    May 1 at 13:45
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    $\begingroup$ @RoryAlsop I believe two is acceptable so long as one does not do it often. It's the ones with 3 or 4 people have a problem with. However, I will say that this person has a track record of low-quality questions or questions that combine too many questions into one post, so there is that. $\endgroup$
    – Deko Revinio
    May 1 at 20:55

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No high-energy photons from the core reach the surface at all. The sun is opaque to these photons 100% of the gamma rays released by nuclear fusion and X-rays from the central part of the sun are absorbed by the dense plasma that forms the sun.

Gamma rays and X-rays are both high-energy photons. The difference is how they are formed: X-rays from the interactions of electrons, gamma rays from the interactions in nuclei (and in the sun, from the fusion of nuclei) Gamma rays tend to have a higher energy than X-rays, although there is some overlap.

The sun is made of fully ionized plasma, there are no "atoms" only atomic nuclei (mostly hydrogen and helium) and a lot of free electrons. In the sun, this plasma is compressed very to form a very dense substance. It is much denser than lead. Lead has a density of about 11g/cm³, the core of the sun has a density of about 160g/cm³. It is this high density of both nuclei and electrons, as much as anything else, that makes the core of the plasma completely opaque to gamma radiation.

The surface of the sun (the level of the atmosphere at which it becomes transparent to light) is at a temperature of about 5800K, and so too cool to emit (more than a negligible amount of) X-rays.

Instead, all the X-rays produced by the sun are emitted by the sun's atmosphere. Here magnetic fields heat the (thin, rarified) plasma to millions of degrees, and it is this superheated plasma that emits X-rays. Gamma radiation can be produced by the interaction of the sun's atmosphere with cosmic radiation.

The X-ray flux is coming from the thin atmosphere and is much lower than the flux of visible light from the sun's surface. (By a factor of about ten million).

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  • $\begingroup$ So, once gamma-ray or x-rays are produced through fusion in the core, they right away are absorbed in the core as well which cause atoms to become ionized in the core. Is this true ? if so, then x-rays and gamma rays would never reach any layer outside the core. $\endgroup$
    – Giorgi Lagidze
    Apr 30 at 8:55
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    $\begingroup$ That's correct. As the other answer says, gamma rays will travel no more than a few mm in the dense plasma of the sun's core. There are no atoms in the core of the sun, the plasma is fully ionised all the time. $\endgroup$
    – James K
    Apr 30 at 9:51
  • $\begingroup$ My source is sws.bom.gov.au/Educational/2/1/3 "Moderate background between 10-7 and 10-6 Watts/sq meter" Levels of flux during a flare are higher. $\endgroup$
    – James K
    Apr 30 at 10:18
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    $\begingroup$ Not one single photon of any frequency or mode of generation from the core ever escapes the sun. None of the spectrum of electromagnetic radiation produced in the cor ever reaches the surface. $\endgroup$
    – James K
    Apr 30 at 20:46
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    $\begingroup$ They are absorbed (after travelling about 1mm, then re-emitted, then re-absorbed, then re-re-emitted, and so on, the energy slowly makes its way out of the core an through the radiative zone. the temperature cools as you move away from the core, so the re-emitted photons have longer wavelength than the initial ones. $\endgroup$
    – James K
    Apr 30 at 21:14
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The photons created by nuclear fusion in the Sun's core are very high energy gamma ray photons (higher frequency than x-rays). These don't travel very far, maybe a few millimeters, before being absorbed and readmitted. This happens over and over and over. The created / absorbed / readmitted photons take a random walk to escape the core, losing average energy but gaining in number on the way out.

It's only in the last few hundred of kilometers of the Sun's photosphere that photons can finally escape the Sun. By that time, the escaping photons are mostly near infrared range. Some are in the visible frequency range, and a very small portion is in the even higher frequency ultraviolet range. Hardly any are X-rays and gamma rays.

That said, the Sun does on occasion emit X-rays and even gamma rays into space. This happens when magnetic field lines break in the extremely thin plasma that lies about the Sun's photosphere. These X-ray producing events tend to happen more frequently during the maxima of the Sun's approximately eleven year long solar cycle, compared to the minima.

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  • $\begingroup$ Question 1: so fusion only produces gamma-rays, not x-rays ? Question 2: if gamma rays produced by fusion is absorbed very son in the near millimeters space, what absorbs it ? hydrogens/carbon or whatever atom is there wouldn't be able to, since gamma rays have high energy and once they hit atom, atom would become ionized, which means near the core, atoms would end up all being ionized which doesn't seem correct. So ? $\endgroup$
    – Giorgi Lagidze
    Apr 30 at 8:46
  • $\begingroup$ or maybe So, once gamma-ray or x-rays are produced through fusion in the core, they right away are absorbed in the core as well which cause atoms to become ionized in the core. Is this true ? if so, then x-rays and gamma rays would never reach any layer outside the core. $\endgroup$
    – Giorgi Lagidze
    Apr 30 at 8:56
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    $\begingroup$ @GiorgiLagidze the interior of the Sun is completely ionised. $\endgroup$
    – ProfRob
    Apr 30 at 10:11
  • $\begingroup$ @GiorgiLagidze There's no boundary between x rays and gamma rays. The only difference between hard x rays and gamma rays is the process that creates the photons. Fusion and particle annihilation by definition creates gammas. Particle-particle collisions that leave the particles intact by definition create thermal photons, which can be very x rays if the temperature is high enough. The temperature at the Sun's core is high enough to result in hard x rays as thermal radiation. $\endgroup$
    – David Hammen
    Apr 30 at 14:56
  • $\begingroup$ TGiorgiLagidze As @ProfRob noted, the Sun's interior is completely ionized. That happens at a million kelvins or so. The Sun's core is about 15 million kelvins. It's mostly free electrons that absorb the gamma photons created by fusion. Those energized electrons quickly interaction with other particles, releasing thermal photons -- in random directions. It's the random direction nature of the emission that results in a random walk that eventually lets the thermal energy escape from the Sun's core. $\endgroup$
    – David Hammen
    Apr 30 at 14:58

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