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Not a scientist so please type your answers slowly. : )

Is the magnetosphere the only thing that can cause bow shock?

Edit: For context:

My research: Wikipedia (I know, I know, just for background) https://en.wikipedia.org/wiki/Bow_shock

NASA https://science.nasa.gov/science-news/news-articles/cosmic-bow-shocks

Science Direct (Elsevier) https://www.sciencedirect.com/topics/engineering/bow-shock

Physics World: https://physicsworld.com/a/bow-shock-no-show-shocks-astronomers/

Writing a sci fi book (as a hobby - tech writer by trade) and trying to do generally realistic science. So no FTL or interstellar travel but magnetic sails and a whole lot of plasma wind. : D

Which led to bow shock, which led to some characters observing the edge of their system and me wondering what happens to the solar winds there.

So based on the Physics World link, bow shock at the confluence of, at least our system and interstellar space, seems to be more of a bow wave. Seems the speed of our system and/or interstellar space are not what we thought it was, thus diminishing the, for lack of a better term, the impact, between the solar winds and their plunge into interstellar space. The article suggest that the magnetic pressure in the interstellar medium is higher than we thought.

So, here's where I am in my layman's understanding, which could be wrong:

The energy emitting from the sun heats plasma (charged particles) to the point the sun's gravity cannot contain it and it is discharged in a radius causing the solar winds. Meanwhile, earth, just minding its own business is busy churning its inner molten iron core which creates a magnetic "bubble" around the earth. This protective layer is more comet shaped than bubble with the head facing the sun (our daytime side) and the tail extending far past the moon. (Is this an effect of the sun's gravity?).

The stream of particles coming from the sun are moving at roughly 1M mph (?). Earth is moving through space at approximately 67000 mph. As the solar winds encounter our magnetosphere the reaction is similar to a ship's bow (earth) traveling through a body of water (the solar winds) and the force of the interaction, like a bow making waves, pushes back the solar winds and forces them to pass around the edges of the head of magnetosphere. Scientist have termed this bow shock. You can see examples of bow shock occurring throughout the galaxy.

At the edge of our solar system, where the solar winds pass through and enter the interstellar medium there was an expectation of bow shock but instead it was far diminished. The two reasons I can deduce for this is that the interstellar medium is moving slower than we thought and magnetic density is higher than we thought.

OK, so to refine my question:

  1. Is bow shock always relative to a magnetosphere or magnetic density.
  2. What causes magnetism in the interstellar medium? The movement/collision/reaction of the molecules/atoms that comprise parts of it?
  3. Is bow shock audible?

Thanks in advance for any help. I know that was a lengthy question.

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    $\begingroup$ It looks like you've already done some research! This is good. Please tell us what you've read about bow shock already, so we don't repeat what you already know. $\endgroup$
    – James K
    Dec 23, 2021 at 1:33
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    $\begingroup$ See my edits above: $\endgroup$
    – PruitIgoe
    Dec 23, 2021 at 11:45

1 Answer 1

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Only half an answer, but too long for a comment; a plasma pyhsicist may write a more comprehensive one:

Bow shocks form when a fast-moving medium hits onto another slower one. It is the outer layer region of the magnetosheath which connects magnetosphere and the surrounding medium, where the velocities homogenize. Broadly - speaking the more-or-less coherent velocity / kinetic energy of the faster medium is converted into other forms of energy, like turbulent velocity, but also wave generation at the bow shock. Bow shocks are not necessarily limited to plasma environments. However in space environments we often do have plasma environments, thus the individual particles are charged. This charge, and the fact that the charges move already are the cause of the magnetic field - even when a plasma is neutral overall, residual motions can cause a net magnetic field. The absence of any magnetic field at all would actually be interesting and surprising.

The position of the bow shock is always relative to the magnetosphere (which is the volume of where the central object dominates the plasma environment and thus the magnetic field). The thickness of the magnetosheath though depends primarily on the magnetic field strength of the central object and the velocities of the surrounding medium and the chemistry.

Classically audible are only density variations in a dense medium, within a frequncy range from 20Hz to 20kHz. Wave frequencies in magnetic fields often are a lot lower frequency (mHz etc). So even when converted into accoustic waves, they would be inaudible infra-sound. Yet one can of course transpose the sound to higher frequencies, and then listen to it. This has been done for the "sound" of Churyumov-Gerasimenkov. Whether or not there actually is a bow shock in the plasma around the solar system - the final words have not been said on that matter; the Voyager probes are only at the edge of it and the only instruments in its vicinity.

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  • $\begingroup$ Thanks for the detailed reply. Asked if it was audible because of the Juno probe over Jupiter recordings - youtube.com/watch?v=8CT_txWEo5I. I thought it was transposed to a frequency we could hear. $\endgroup$
    – PruitIgoe
    Dec 23, 2021 at 14:58
  • $\begingroup$ If you look at jpl.nasa.gov/news/… the sound recording does not seem transposed for Juno (100Hz...10kHz) - just the magnetic fluctations converted to sound. $\endgroup$ Dec 23, 2021 at 15:00
  • $\begingroup$ Oh thanks. Interesting stuff. $\endgroup$
    – PruitIgoe
    Dec 23, 2021 at 15:03

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