The sun is simple. Part Two: Radio Emission Mechanisms

I continue the topic started earlier . The article received a lot of feedback, including through habraposhta and ICQ. Many expressed useful additions and corrected some inaccuracies in the article. Thank you very much for this!
In this part, I would like to talk a little about the mechanisms of radio emission, how it arises and what it generally happens :). Well, as a seed for the future, several photographs of the active regions of the Sun, which I obtained using the Nobeyama radio telescope:


So, about the mechanisms of radio emission :)
Electromagnetic radiation creates any accelerating charged object, be it a proton or an electron. Since the electron mass is many times smaller than the proton mass, then the electron will radiate much stronger. Why is that? We can calculate the radiation power of a charged particle using the Larmor formula:

Here q is the charge, a is acceleration and c is the speed of light in a vacuum. We will also use Newton's second law and as a result we obtain that the smaller the mass, the greater the radiation. By the way, it emits an electron 4 million times stronger than a proton.

Elementary Electromagnetic Radiation Mechanisms

1. Brake

With this mechanism of radiation, the medium acts on a moving charge. Coulomb (long-range) collisions lead to acceleration or deceleration of charge. Accordingly, the electron begins to radiate.

2. Cherenkovsky

To understand the principle of this mechanism, it suffices to present an analogy with a shock wave from an airplane or a wave created by a boat (boat, rod) moving through water.
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3. Bendable (magnetic drift)

I think many people remember the movement of a body along a curving line from a school (or institute) physics course (each point of such a line has a radius of curvature, for a circle it has a radius). Actually this acceleration is from there :)

4. Radiation in lines

Radiation occurs due to energy transitions in molecules and atoms.

5. Magnetic braking

On the Sun in the active regions (AO), the main radiating mechanism is precisely the magnetobraking mechanism of radiation. Let's tell about it more.

Magnetic braking radiation is determined by the fact that when an electron moves in a magnetic field at an angle to the line of force (this angle is called the pitch angle), the trajectory of the electron is a spiral line with an axis along the magnetic field line. When designing this spiral line on a plane perpendicular to the magnetic field vector B, a circle is formed. As the electron moves in a magnetic field, the Lorentz force acts on it:

The frequency of rotation of the electron around the circumference is gyrofrequency:

Depending on the speed of the electron, there are three types of magnetic bremsstrahlung. If the emitting particle is weakly relativistic, then the radiation is cyclotron. In such cases, the energy of the emitting particle is much less than the rest energy of the particle. If the particle is ultrarelativistic, then the radiation is called synchrotron. In this case, the energy of the emitting particle is much greater than the rest energy of this particle. Cyclotron and synchrotron radiation are two extreme types of brake light. There is an intermediate type of braking radiation - gyro-synchrotron radiation. In this case, the radiating particle is moderately relativistic, and the energy of motion of such a particle is comparable to its rest energy.
The frequency spectrum of gyro-synchrotron radiation is this:

Conventionally, the frequency spectrum is divided into 3 areas: optically thick, optically thin modes and a mode in which the value of the optical thickness is close to 1. In the phase of the growth of the frequency spectrum, the value of the optical thickness is much greater than 1 (the source is in the optically thick mode) in the high frequencies the value of the optical thickness is much less than 1 (the source is in the optically thin mode). In the vicinity of the highest intensity of radio emission, the optical thickness is of the order of 1.

At this, the introductory part is completed, in the following parts will be the Sun itself and a description of what is happening there :)

And finally:

Wiki reference for the article:
1. About energy levels read here
2. Relativistic - close to the speed of light
3. Resting energy - E = mc ^ 2
4. Frequency spectrum - the dependence of the intensity of radio emission on the frequency of the generated radiation
5. Optical thickness is a quantity that characterizes the attenuation of light in the medium due to its absorption and scattering.
6. Why an electron radiates during acceleration: read here or Ginzburg "Theoretical Physics and Astrophysics".

Books on the subject:
1. Zheleznyakov V.V. "Radiation in astrophysical plasma".
2. Kraus J.D. "Radio astronomy".
The second book is much simpler :) first for maniacs :) See you there!