Magnetic fields play larger role in star formation than previously thought

Sep 09, 2009

The 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 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 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 .) 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 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 arxiv.org/abs/0908.1549

Source: Harvard-Smithsonian Center for Astrophysics (news : web)

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User comments : 12

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plasma_guy
3.3 / 5 (8) Sep 09, 2009
A magnetic field only works on electrical charges in the gas. Granted that there is ionizing radiation in space, but the molecular cloud suggests ionization ratio is still low. So magnetic fields should have a low influence.
omatumr
2 / 5 (4) Sep 09, 2009
THE SUN'S MAGNETIC FIELD IS ANCIENT AND DEEP SEATED

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
gmurphy
2.6 / 5 (5) Sep 09, 2009
ionization is present anywhere lots of particles collide, a molecular cloud seems like a good candidate for this.
earls
1.7 / 5 (6) Sep 09, 2009
Imagine that, another victory for plasma cosmology.

"A magnetic field is produced by moving electrical charges."

"The magnetic fields tended to line up in the same direction"
solrey
1.8 / 5 (5) Sep 09, 2009
The evidence continues to mount, doesn't it earls?

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.
Question
2.3 / 5 (7) Sep 09, 2009
Now move onto galaxy size magnetic fields, then onto magnetic fields in the order of galaxy clusters. Couldn't the core of rotating spiral galaxies be dominated by a strong magnetic field? This magnetic field could create matter and antimatter from particle collisions. Then the positive matter would spew out one pole, the negative out the other. Other near by galaxies could be doing the same thing. What you could end up with is new matter and antimatter galaxies over the eons.

omatumr
1.8 / 5 (5) Sep 09, 2009
MAGNETIC FIELDS AT CENTERS OF STARS AND GALAXIES

Now move onto galaxy size magnetic fields, then onto magnetic fields in the order of galaxy clusters. Couldn't the core of rotating spiral galaxies be dominated by a strong magnetic field? This magnetic field could create matter and antimatter from particle collisions. Then the positive matter would spew out one pole, the negative out the other. Other near by galaxies could be doing the same thing. What you could end up with is new matter and antimatter galaxies over the eons.


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
brant
3.1 / 5 (8) Sep 09, 2009
A magnetic field only works on electrical charges in the gas. Granted that there is ionizing radiation in space, but the molecular cloud suggests ionization ratio is still low. So magnetic fields should have a low influence.


A plasma only needs 1% ionization to be considered plasma....
pseudophonist
3.3 / 5 (4) Sep 10, 2009
Magnetic fields also affect certain molecules depending on the orientation of the spins of the electrons (particularly unpaired electrons like in O2). In addition, a strong field can affect 'neutral' molecules because they are made of protons and electrons. Finally in strong fields, there can be orbital splitting which has further consequences.

So the statement that magnetic fields onyl works on electric charges is a little misleading
plasma_guy
5 / 5 (5) Sep 10, 2009
Well I appreciate the arguments for magnetic effects but besides charge the velocity is important, so generally the electrons in the plasma would respond to magnetic fields (spiraling around the lines). The ions are generally assumed to only respond to the electric fields due to their slower velocity.

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.
omatumr
2.5 / 5 (4) Sep 11, 2009
CONNECTED MAGNETIC FIELDS OF SUN AND EARTH

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
brentwuli
not rated yet Sep 21, 2009
to plasma_guy

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!