* Astronomy

Magnetic fields set the stage for the birth of new stars

Astronomers at the Max Planck Institute for Astronomy have, for the first time, measured the alignment of magnetic fields in gigantic clouds of gas and dust in a distant galaxy. Their results suggest that such magnetic fields play a key role in channeling matter to form denser clouds, and thus in setting the stage for the birth of new stars. The work will be published in the November 24 edition of the journal Nature.
Astronomers know quite a bit about these so-called molecular clouds: They consist mainly of hydrogen molecules - unusual in a cosmos where conditions are rarely right for hydrogen atoms to bond together into molecules. And if one traces the distribution of clouds in a spiral galaxy like our own Milky Way galaxy, one finds that they are lined up along the spiral arms.
But how do those clouds come into being? What makes matter congregate in regions a hundred or even a thousand times more dense than the surrounding interstellar gas?
One candidate mechanism involves the galaxy's magnetic fields.
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Title: The Origin of Magnetic Fields in Galaxies
Authors: Rafael da Silva de Souza, Reuven Opher

Microgauss magnetic fields are observed in all galaxies at low and high redshifts. The origin of these intense magnetic fields is a challenging question in astrophysics. We showed that the natural plasma fluctuations in the primordial universe, produces random dipole magnetic fields of comoving size ~1 pc and intensity ~ 0.1 \mu G at a redshift z ~ 10. The theory predicts an average magnetic field ~ 0.003 ~ nG over a 2 kpc region at z ~ 10. We assume this seed field and examine its amplification by a turbulent dynamo in a protogalaxy.
Whereas the standard \alpha-\Omega dynamo for a typical disk galaxy creates only a 2 e-fold amplification of the field in ~ 10^{9} years, the turbulent dynamo has a much shorter amplification time. Starting with the average seed magnetic field of B ~ 0.003 nG over ~ 2 kpc at z = 10, we find that in 10^{9} years, B is amplified to ~ 1 nG. This corresponds to a ~ 6 e-fold amplification of the field. In the process of collapsing to form galaxies at z ~10, the plasma density rises by a factor of ~ 200 and the magnetic fields, by a factor of ~ 34. Thus, 0.03 \mu G fields over 0.34 kpc regions in galaxies are predicted. If the dipole magnetic fields predicted by the Fluctuation-Dissipation-Theorem are not completely random, microgauss fields over regions \gtrsim 0.34 kpc are easily obtained. The model is thus a strong candidate for resolving the problem of the origin of magnetic fields in \lesssim 10^{9} years in high redshift galaxies.

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