Magnets Help Make Stars

Gravity sometimes needs a helping hand. New findings show that the giant clouds of dust and gas that pervade the universe, out of which form all of the stars and other assorted celestial bodies, depend on magnetism to condense. If confirmed, the study would resolve a long-standing mystery about the star-forming process.

Astronomers have argued for years about how stars condense out of the diffuse clouds of dust and gas called nebulas. One camp maintains that turbulence within the clouds plays a dominant role. It breaks up the uniformity of the nebulas, the hypothesis goes, allowing gravity to pull matter together into clumps and eventually compress them into stars and their planetary systems. Another group asserts that the clouds are too diffuse for gravity alone to convert them into massive objects such as stars--so a second force must be at work.

Attraction at work. Magnetic fields help gravity to form new stars, such as these in the Coronet cluster.

The likely candidate is magnetism. According to the idea, the movement of electrically charged atoms in the clouds forms a magnetic field, which dampens turbulence and allows gravity to collapse parts of molecular clouds into new stars and solar systems.

The problem with both ideas is that the nebulas are so distant and wispy that they cannot be observed in sufficient detail. So until now, most of the work in this area has been theoretical.

Now, a team led by astronomer Hua-bai Li of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, has developed a simple way to gather the critical data directly. Using existing observations, the researchers analyzed the polarized light emissions from 25 dense areas within several nebulas that are up to 6500 light-years from Earth. Polarized light's electrical properties can reveal the presence and alignment of magnetic fields.

In most cases, the team reports in a paper accepted for publication in The Astrophysical Journal, the polarized light from the dense patches lined up exactly with polarized light from the entire nebula. If turbulence were dominating the process, the researchers conclude, the picture would have been much more chaotic. So magnetism must be dominating the structure of both the nebulas and their dense patches, and therefore it is regulating the starmaking process, the team argues.

The study provides "new, exciting, and surprising evidence" that magnetic fields control the process of star formation, says astronomer Daniel Apai of the Space Telescope Science Institute in Baltimore, Maryland. The findings show that magnetism, not turbulence, is dominating the process, he says. It's "similar to a Zen garden," he says, where "grooves in the sand are all aligned in the same direction," revealing "evidence for a larger-level organization."

By Phil Berardelli
ScienceNOW Daily News
10 September 2009


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