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Basic Question about Star Formation

  1. Aug 18, 2010 #1
    I'm trying to find some information about models of star formation (just out of curiosity). I only have a basic knowledge of text-book physics and calc, so it's hard to get started. In particular, I'd like to know how the theory is tested. The only prediction of Nebula theory that I can think of, is that planets would all orbit on the same plane, and the same direction. Are there any other more clever testable predictions?
  2. jcsd
  3. Aug 18, 2010 #2
    I'm not clear on just what you're asking... is it about how a dust cloud accumulated and what triggers it's collapse and eventual fusion, or the nature of protoplanetary discs? the latter is just a matter of the disk being the remnants of the what the star had for an accretion disk, and therefore has angular momentum in a single plane.
  4. Aug 18, 2010 #3
    I just want to know what observations support the theory, and what testable predictions it makes. For example, the CMB, and chemical composition of the universe, are often cited as predictions of the Big Bang theory.

    Similarly, what kind of observations support the nebula model? Since we can't watch these events unfold, it seems that these kinds of observations are important.
  5. Aug 18, 2010 #4
    You've raised a central problem with the theory, which is the lack of observation during critical periods. The "dust", as it seems you already know, becomes too dense and blocks information that we can use. The best that can be said is that the evidence exists in the results we observe, but there is no CMB or other "photo" to show it. There are questions, especially about the dynamics at play in the formation of super-massive stars that have viable answers in theory, but not evidence.

    Does this help?
  6. Aug 18, 2010 #5


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    One of the key open questions in the physics of star formation is what regulates the earliest stages of it -- the gravitational collapse of the dense molecular cloud cores that form into stars. Observations of these cores suggest that they last longer than a free-fall timescale, which in turn suggests that something other than just gravity is at play (i.e. something is acting to slow down the gravitational collapse of these structures). Leading candidates include magnetic fields, and turbulent motions within the clouds. But which of these mechanisms is the most important, i.e. which one dominates in regulating the collapse? Different theoretical models can be constructed that assume different answers to that question. These models make different predictions about the strengths of the magnetic fields within the molecular clouds, about how ordered or disordered these magnetic fields would be on various scales, and about how much of a correlation there would be between the orientation of the magnetic fields, and the orientation of the physical structures within the cloud. If we could somehow carry out observations to map out the directions of the magnetic fields within these molecular clouds on a range of physical scales, then we could begin to test these predictions and therefore constrain the theoretical models somewhat. That's all I know on the subject. I don't work in the field and hence I'm not an expert.

    EDIT: I didn't intend to imply that we couldn't carry out such observations. Many people are trying to do so. One method of mapping out the magnetic field directions is to do polarimetry (measurement of the polarization of EM radiation) at submillimetre wavelengths. This can be done because dust grains tend to align preferentially in the direction of the magnetic field, and the presence of a preferred dust grain alignment leads to the thermal emission from those dust grains being linearly polarized. Said emission is in the submillimetre because the dust is cold.
    Last edited: Aug 18, 2010
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