Galaxy is Surprisingly Magnetic
The precision of the Robert C. Byrd Green Bank Telescope in Green Bank, West Virginia, which can be pointed with an accuracy of one arcsecond - equivalent to the width of a single human hair seen six feet away - enabled the astronomers to measure the magnetic field of a single galaxy.
Credit: NRAO/AUI

A radio telescope that stands taller than the Statue of Liberty has detected an unexpectedly strong magnetic field as it appeared 6.5 billion years ago in a young galaxy.

Astronomers have long thought that magnetic fields grow very gradually from slowly rotating galaxies over 5 billion to 10 billion years, but the strong field finding may force some rethinking. Detected in a distant protogalaxy, it measures at least 10 times greater than the average magnetic field in the Milky Way.

?This was a complete surprise,? said Arthur Wolfe, a physicist at the University of California, San Diego, who headed the team that hailed from several UC campuses. ?The magnetic field we measured is at least an order of magnitude larger than the average value of the magnetic field detected in our own galaxy.?

Magnetic fields help control the rate of star formation and the dynamics of interstellar gas within galaxies. But until recently, astronomers knew very little about magnetic fields outside our own galaxy. They had previously measured a weaker magnetic field in only one nearby galaxy.

However, a different team of Swiss and American astronomers previously made indirect measurements suggesting that the magnetic fields of young galaxies were as strong back in the early universe as they are in mature galaxies today.

The team behind the new study, detailed in the Oct. 2 issue of the journal Nature, used the world?s largest fully steerable radio telescope for their measurements — the Robert C. Byrd Green Bank Telescope in Green Bank, W. Va., operated by the National Science Foundation?s National Radio Astronomy Observatory. The finding represents the first direct measurement of an early galaxy's magnetic field.

The young protogalaxy they probed, DLA-3C286, is located in a region of the northern sky that is directly overhead during the spring in the northern hemisphere.

Wolfe said the earlier indirect measurements and his team?s latest direct measurement of a distant galaxy?s magnetic field do not necessarily cast doubt on the current leading theory of magnetic field creation. That mean-field-dynamo model predicts that magnetic field strengths started out much weaker than they are today.

"Our results present a challenge to the dynamo model, but they do not rule it out," he added. "Rather the strong field that we detect is in gas with little, if no, star formation, and an interesting implication is that the presence of the magnetic fields is an important reason why star formation is very weak in these types of protogalaxies."

Wolfe said his team has two other plausible explanations for what they observed.

"We speculate that either we are seeing a field toward the central regions of a massive galaxy, since magnetic fields are known to be larger towards the centers of nearby galaxies," Wolfe said. "It is also possible that the field we detect has been amplified by a shock wave generated by the collision between two galaxies."

Astronomers hope to extend their magnetic field observations further to better understand their influence on the evolution of galaxies.

"The challenge now is to perform observations like these on galaxies throughout the universe," said J. Xavier Prochaska, another team member and a UC Santa Cruz astronomer.