Magnetic fields play larger role in star formation than previously thought
September 9, 2009The simple picture of star formation calls for giant clouds of gas and dust to collapse inward due to gravity, growing denser and hotter until igniting nuclear fusion. In reality, forces other than gravity also influence the birth of stars. New research shows that cosmic magnetic fields play a more important role in star formation than previously thought.
A molecular cloud is a cloud of gas that acts as a stellar nursery. When a molecular cloud collapses, only a small fraction of the cloud's material forms stars. Scientists aren't sure why.
Gravity favors star formation by drawing material together, therefore some additional force must hinder the process. Magnetic fields and turbulence are the two leading candidates. (A magnetic field is produced by moving electrical charges. Stars and most planets, including Earth, exhibit magnetic fields.) Magnetic fields channel flowing gas, making it hard to drawn the gas from all directions, while turbulence stirs the gas and induces an outward pressure that counteracts gravity.
"The relative importance of magnetic fields versus turbulence is a matter of much debate," said astronomer Hua-bai Li of the Harvard-Smithsonian Center for Astrophysics. "Our findings serve as the first observational constraint on this issue."
Li and his team studied 25 dense patches, or cloud cores, each one about a light-year in size. The cores, which act as seeds from which stars form, were located within molecular clouds as much as 6,500 light-years from Earth. (A light-year is the distance light travels in a year, or 6 trillion miles.)
The researchers studied polarized light, which has electric and magnetic components that are aligned in specific directions. (Some sunglasses work by blocking light with specific polarization.) From the polarization, they measured the magnetic fields within each cloud core and compared them to the fields in the surrounding, tenuous nebula.
The magnetic fields tended to line up in the same direction, even though the relative size scales (1 light-year cores versus 1000 light-year nebulas) and densities were different by orders of magnitude. Since turbulence would tend to churn the nebula and mix up magnetic field directions, their findings show that magnetic fields dominate turbulence in influencing star birth.
"Our result shows that molecular cloud cores located near each other are connected not only by gravity but also by magnetic fields," said Li. "This shows that computer simulations modeling star formation must take strong magnetic fields into account."
In the broader picture, this discovery aids our understanding of how stars form and, therefore, how the universe has come to look the way it is today.
More information: The paper detailing these findings has been accepted for publication in the Astrophysical Journal and is available online at http://arxiv.org/abs/0908.1549
Source: Harvard-Smithsonian Center for Astrophysics (news : web)
Aug 11, 2006 |
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The Sun's magnetic field is also deep-seated and ancient, probably arising from the core material on which it accreted.
See: "Superfluidity in the solar interior: Implications for solar eruptions and climate, " Journal of Fusion Energy 21 (2002) 193-198
http://arxiv.org/...501441v1
With kind regards,
Oliver K. Manuel
http://www.omatumr.com
"A magnetic field is produced by moving electrical charges."
"The magnetic fields tended to line up in the same direction"
I'll add to your two quotes with:
"Our result shows that molecular cloud cores located near each other are connected not only by gravity but also by magnetic fields," said Li. "This shows that computer simulations modeling star formation must take strong magnetic fields into account."
Looks like a fractal network of Birkeland currents.
That is an interesting idea. Neutron stars at the centers of stars and galaxies may explain the observations.
With kind regards,
Oliver K. Manuel
http://www.omatumr.com
A plasma only needs 1% ionization to be considered plasma....
So the statement that magnetic fields onyl works on electric charges is a little misleading
I would buy the magnetic effect only for extensive plasma not a molecular cloud. Maybe they can use spectroscopy to confirm.
The paper uses very indirect simulation-based evidence for magnetic fields, in my opinion, and ignores the most fundamental required comparison: gravitational vs. magnetic influence. Undoubtedly long-distance electro-magnetic fields should win hands down.
The link between the Earth's magnetic field and that of the Sun have been discussed recently on Physics World and on the NASA website:
http://tinyurl.com/2ntass
http://tinyurl.com/dx3qlk
With kind regards,
Oliver K. Manuel
http://www.omatumr.com
I got two points
1. Note where the electric fields point to: electrons trapped by the magnetic fields !
2. Gravity always wins:
Assuming a uniform distribution of mass and magnetic field. Since mass is proportional to the 3rd power of linear scale while magnetic flux is to the 2nd power, given a field strength, one can always find a scale such that gravitational energy over comes field energy! And a collapse can happen at this scale.
The point of this paper, I think, is about the forces regulating this collapse. Turbulence undoubtedly plays a role, while magnetic field is more controversial, owing much to the lack of observation evidence. This paper shows that field is not weaker that turbulence!