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I The Role of magnetic field during the formation of small to medium scale stars

  1. Mar 14, 2018 #1
    Hi, I would like to raise a question about Role of magnetic field while formation of small to medium scale stars emerging from nebula ?
     
  2. jcsd
  3. Mar 14, 2018 #2

    berkeman

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    Staff: Mentor

    Welcome to the PF.

    Can you post links to the reading you have been doing so far? Also, you have used the "A" prefix for this thread, which means you want to discuss it at a PhD level. Would you prefer that we change the prefix to "I" for a more undergraduate-level discussion, or do you still prefer "A"?

    Thanks! :smile:
     
  4. Mar 14, 2018 #3

    davenn

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    indeed

    But as a starting point, I would consider that gravity is the overwhelmingly predominant force
     
  5. Mar 14, 2018 #4
  6. Mar 15, 2018 #5

    JMz

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    Please clarify: Are you asking if magnetic fields influence the formation of medium- & low-mass stars? Or if the fields influence their emergence from the proto-stellar nebula (Herbig-Haro stage, for instance)?
     
  7. Mar 15, 2018 #6
    I am intrigued that you clearly understood what I was talking about.:smile:

    I am Concerned about the magnetic fields influence on the formation of medium and low mass star. And also searching is there any relation between fields influence on the star and there emergence from the nebula.
     
  8. Mar 15, 2018 #7

    JMz

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    In most situations, magnetic fields "come along for the ride", especially during the collapse of a gas cloud into a proto-star. In particular, if the molecular cloud collapses to form any stars at all, then my understanding is that gravity is typically a much bigger effect than magnetic fields, except perhaps very locally. (E.g., the immediate vicinity of a pulsar would not be a likely place for a proto-star to form. However, the magnetic field isn't the only reason for that.)

    I have seen hypotheses that magnetic fields are important for clearing the proto-stellar nebula (and shutting down planet formation), though I don't know the current state of research on that. There are multiple mechanisms to form jets near the proto-star, not only magnetic fields. However, the fields do seem to be important for HH objects, which are themselves a normal part of low-mass star formation: see https://en.wikipedia.org/wiki/Herbig–Haro_object.
     
  9. Mar 16, 2018 #8

    I see your hypotheses seems fair enough but I have another one as we have known the existence of magnetic properties of elements from last few decades, I think that its the electromagnetic forces that brings together few of the particle together in a nebula after which the gravitational contraction begins as gravity plays its role due to which the cluster of particle gets a spin as other particle hits it and joins it due to this constant bombardment heat is produced which some how creates a magnetic field and according to me the magnetic helps the form of star as this " It stops the charged particles (possibly electron clouds), due to which stable atoms gets attracted and the heat due to bombardment and rotation kicks off fusion".

    My thought seems childish but its got its own merit as by my hypotheses one can explain the accumulated electron clouds near medium and low mass star.
     
  10. Mar 16, 2018 #9

    davenn

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    please provide links to reputable papers on this
    personal theories are against PF rules
     
  11. Mar 16, 2018 #10
  12. Mar 16, 2018 #11

    JMz

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    Two things to keep in mind: (1) For practical purposes, the nature of the atoms does not matter -- for instance, iron and hydrogen are about equally irrelevant: Both nuclei are much more massive than electrons (though iron may ionized more easily, producing free electrons). Magnetic fields in gases and plasmas are caused by macroscopic electrical currents, mostly free electrons.
    (2) The collapse of a gas cloud is initially caused by (a) collision with another cloud or (b) cooling until its pressure is weaker than its gravity or (c) radiation pressure on one side, causing a build-up of density on the opposite side. Electromagnetic effects (except for the photons in (c)) have nothing to do with starting the collapse.
     
  13. Mar 16, 2018 #12

    JMz

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    In terms of my last response, note that (a) this abstract deals with magnetic fields in proto-stars that have already formed, not fields in gas clouds, and (b) stars and proto-stars are plasmas.

    It may help to realize that, if magnetic flux is conserved (i.e., the currents never meet and cancel with large release of heat), then a Sun-sized star's magnetic field will be >~ 10^15 times as large as in the cloud. (A molecular cloud may typically have ~ 1 solar mass per cubic light year, and 1 LY ~ 10^7 solar diameters.) Thus, the mere fact that the plasma collapsed from a light year to a solar diameter means than the field is compressed enormously. It does not necessarily mean that the field influenced the collapse significantly.

    You may find the abstract here http://iopscience.iop.org/article/10.1086/318290 to be helpful.
     
  14. Mar 31, 2018 #13
    There's a problem in the theory of protostellar collapse, and that is that angular momentum precludes the collapse from proceeding. Efforts have been made to solve this problem by means of what's called "ambipolar diffusion" - the decoupling of molecular hydrogen from the plasma that it's collisionally coupled to - and a concept called "flux freezing" - where the magnetic field of the protostar is "frozen" in the surrounding disk. The orbital velocity of the disk being smaller than the rotational velocity of the protostar, the disk slows down the protostar by way of the frozen magnetic field, the disk gaining angular momentum as the star loses it.
     
  15. Apr 2, 2018 #14

    Sir, Will you be able to refer me some articles regarding this.
     
  16. Apr 2, 2018 #15
    I don't have anything specific, but if you search "ambipolar diffusion" on "adsabs.harvard.edu" you may find what you're looking for - good luck!
     
  17. Apr 2, 2018 #16
    Last edited: Apr 3, 2018
  18. Apr 5, 2018 #17
    Also search "adsabs.harvard.edu" for "magnetic braking"!
     
  19. Apr 8, 2018 #18
    P.S. - Use the "beta" format
     
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