Young Galaxies Surprisingly Magnetic
Image of the spiral galaxy M51 overlaid with contours of the total radio intensity. The small vector lines represent the direction of the magnetic field at each point.
Credit: MPIfR Bonn and Hubble Heritage Team

Galaxies much like ours harbor mysterious magnetic fields, which turn out to build up much faster than scientists realized, a new study has found.

By analyzing light coming from distant galaxies at a time early in the universe's history, astronomers were able to show that these galaxies developed magnetic fields much sooner than expected. The finding may force scientists to rethink their understanding of how magnetic fields grow inside galaxies.

"The magnetic fields in these galaxies were very strong, at least as strong as they are today, at a time when the age of the universe was only one third of its current age," said researcher Francesco Miniati of the Swiss Federal Institute of Technology. "That puts strong constraints on the evolution of magnetic fields."

The discovery was made with the help of faraway light sources that served to illuminate the galaxies being studied.

Miniati and his colleagues used the European Southern Observatory?s Paranal Observatory to observe the very distant bright objects, called quasars, in both visual and radio frequency light. Quasars are the central regions of some galaxies where supermassive black holes generate tremendous emissions across the electromagnetic spectrum, from radio waves to visible light and x-rays.

The radio waves the researchers observed often showed signs of having passed through a magnetic field. It turned out, when a normal galaxy lay between Earth and the quasar, the magnetic field signature on the light was most strong. This told the researchers that it was the foreground galaxies, and not the quasars, that held the responsible magnetic fields.

"We were surprised that we could actually measure this so cleanly, and we were surprised that these galaxies had such strong magnetic fields early on," Miniati told "This has been suggested before, but seen convincingly only for some individual galaxies. What we were able to show with this measurement is that all regular galaxies early on have these kinds of strong magnetic fields."

Scientists think galactic magnetic fields start from tiny magnetic seeds, perhaps created inside stars or quasars, and are then amplified over time as the turbulent movement of galactic gas, stirred up by stellar explosions, and the galaxy's rotation cause the magnetic fields to grow. This standard picture, however, can only account for strong magnetic fields that build up slowly over time. The new finding means scientists must come up with an improved explanation for how magnetic fields build up inside galaxies in the young universe such as those Miniati and his team observed.

The researchers detailed their discovery in the July 17 issue of the journal Nature. The study was funded by the Swiss National Science Foundation, the Natural Sciences and Engineering Council of Canada and the U.S. Department of Energy.