The sun is simple. Part Four: Oscillations on the Surface of the Sun

    In my previous parts: 1 2 and 3, I talked about research tools, radio emission mechanisms, and briefly talked about solar flares. Today I will continue this series of topics and talk about helioseismology, that is, about fluctuations in the Sun. Below is a video of the oscillating portion of the active region of the Sun:

    Earth seismology is based on the characteristics of the propagation of sound underground. However, a seismograph (a device that records soil vibrations) cannot be placed on the Sun. Therefore, the oscillations of the Sun are measured by completely different methods. The main one is based on the Doppler effect. Since the solar surface rhythmically falls and rises (oscillates), then its approach-removal affects the spectrum of emitted light. By studying the spectra of different parts of the solar disk, we get a picture of the velocity distribution; Of course, with time it changes - the waves run. The periods of these waves are in the range of about 3 to 10 minutes. When they were first discovered, the found value of the period was approximately 5 minutes. Since then, all these fluctuations have been called “five-minute.” In the sixties of the 20th century, astronomers discovered

    Helioseismology opened a new path to the study of the inner layers of the Sun. Constant wave motions, like seismic waves on Earth, shake the bowels of the sun. As geophysicists study seismic waves to understand the conditions inside the Earth, so solar physicists use the vibrations observed on the surface of the Sun to obtain information about its internal structure. In the gaseous medium of the Sun, compression and rarefaction waves — acoustic waves — and internal gravitational waves, in which gravity is the returning force, can propagate. The focus is on acoustic waves, as they are better observed. The propagation of acoustic waves within the sun cannot be directly observed. However, under the influence of waves reaching the surface of the Sun, the outer layer of gas begins to rise and fall.

    Helioseismology consists of three areas:
    1. Seismology of the Sun as a whole.
    2. Seismology of photospheric structures.
    3. Seismology of coronal structures.

    Seismology of Coronal Structures

    What is the crown of the sun?

    The corona is the uppermost, hottest part of the solar atmosphere, the structure of which is determined by magnetic fields.
    The corona of the sun consists of an almost completely ionized plasma of a mixture of hydrogen and helium with a temperature of more than a million degrees.

    Coronal structures

    1. Open coronal structures
    - Coronal holes;
    - streamers;
    - Feathers inside coronal holes;

    2. Closed coronal structures
    - Hot and tight loops

    3. Other
    - Jets
    - Prominences

    Oscillation of coronal loops generated by flares

    More than twenty examples of such fluctuations were found, one of which is presented in the video at the very top of the post. For its huge size and outstanding amount of energy released, the flash was even nicknamed the “Bastille Day”.
    The periods of the obtained oscillations are about 4 minutes, the oscillations are close to harmonic, the decay time is 3-4 periods.

    Wiki article:
    1. Seismology - the science of the propagation of seismic waves.
    2. Doppler effect - a change in the frequency and wavelength recorded by the receiver, caused by the movement of their source and / or the movement of the receiver.
    3. Prominences - dense condensations of relatively cold (compared to the solar corona) substances that rise and are held above the surface of the Sun by a magnetic field.
    4. Oscillations - oscillations.

    Literature on the article:
    1. Zheleznyakov VV "Radiation in astrophysical plasma."
    2. Kraus J.D. "Radio astronomy."

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