“This means that magnetism is generated very early in a galaxy’s life by natural processes, and thus that almost every heavenly body is magnetic,” said Bryan Gaensler, an astronomer with the University of Toronto who co-authored a paper about the discovery, in a statement. “The implication is that we need to understand magnetism to understand the universe.”
Galaxies have very weak magnetic fields — about a million times weaker, for example, than the Earth’s magnetic field. But magnetism is thought to play an important role in the physics of the interstellar medium in galaxies, shaping how gas flows in spiral arms, around bars, and in galaxy halos. Magnetic fields are also essential for the onset of star formation.
“But nobody knows where cosmic magnetism comes from or how it was generated,” Gaensler remarked. “But now, we have obtained a major clue needed for solving this mystery, by extracting the fossil record of magnetism in a galaxy billions of years before the present day.”
This wasn’t a “chance” detection. Magnetic fields can’t be detected directly. The only way to identify them is through lensing events. The researchers used a coincidental alignment where light from a bright and distant quasar passing through the galaxy being studied — known as gravitational lensing — enabled these very difficult observations.
“We targeted a list of objects already known to be gravitational lenses, looking for magnetic effects,” Gaensler told Seeker in an email. “Some of them didn’t work out, some we’re still analyzing, and with this one we hit paydirt.”
Left: Hubble Space Telescope image of the gravitational lensing system CLASS B1152+199. The background quasar is lensed by the foreground galaxy into two images A and B. Right: Faraday rotation of the lensed images. Image A probes a sight line through the less dense outskirts of the lensing galaxy with a weaker magnetic field, while Image B probes through a sight line closer to the center of the galaxy with higher gas density and stronger magnetic field.
As light from the quasar traveled toward Earth, its path was bent by the gravity of CLASS B1152+199, similar to how the trajectory of a spacecraft is changed as it flies by a planet. The bent light from the quasar traveled along different paths, creating multiple observations, which the team said was key to getting the measurements they needed.
Using the Karl Jansky Very Large Array in New Mexico, the team was able to measure a property of the radio wavelengths of light called polarization that changed when passing through the magnetic field of the foreground galaxy. The astronomers measured this change, called the Faraday rotation effect, of the lensed quasar images to show that the lensing galaxy hosts a discernible large-scale magnetic field.
They were able to determine that the young galaxy CLASS B1152+199 has a magnetic field similar in current configuration to the Milky Way. The results, published in Nature Astronomy, indicate that galactic magnetic fields may take shape early on in a galaxy’s lifetime and remain stable as it evolves.
Magnetic fields occur due to dynamo processes where the mechanical energy from rotating and convecting fluids or gases is transformed into magnetic energy. In the case of Earth, the sloshing flow of liquid iron in our planet’s core generates electric currents, which in turn produce magnetic fields.
In stars, the magnetic field is produced by rotating ionized gas. How the dynamo operates in large-scale structures like galaxies and how it creates a magnetic field is not well understood, but is thought to be tied to the circulation and turbulence within the interstellar gas.
This new detection of a strong magnetic field in a galaxy when the universe was about two-thirds of its current age provides an indication of how fast these fields grow in galaxies.
“Although this distant galaxy had less time to build up its magnetic field compared to local galaxies, it still managed to do so,” said lead author Sui Ann Mao from the Max Planck Institute for Radio Astronomy in Bonn. “The results of our study support the idea that galaxy magnetic fields are generated by a dynamo process.”
To confirm their findings and better understand galactic magnetic fields, the team will continue their observations.
“At the moment we have a sample of one object,” Gaensler said via email. “We are thinking this galaxy is a typical example of galaxies in the universe, but we now need to find more to see if what we are seeing here is borne out elsewhere. Plus we want to go back further in time, to look at even younger galaxies, to see their magnetic fields turning on and then growing as they age.”