An international group of physicists has measured the most distant galactic magnetic field that belongs to a young galaxy, named CLASS B1152+199, that is located five billion light-years from Earth. Previously scientist thought that magnetism in galaxies starts off weak but becomes stronger and more organized over time, but the data collected from mention star says differently. This new discovery is providing intriguing clues about the evolution of magnetism in the unfolding universe.
Galaxies have very weak magnetic fields about a million times weaker 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.
Bryan Gaensler, an astronomer with the University of Toronto who co-authored a paper about the discovery, said “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, The implication is that we need to understand magnetism to understand the universe. Problem is nobody knows where cosmic magnetism comes from or how it was generated. 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.”
Magnetic fields can’t be detected directly. The only way to identify them is through lensing events. The researchers are using gravitational lensing to study the magnetic field. Astronomers 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.
As light from the quasar travelled 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 travelled along different paths, creating multiple observations, which is the key to getting the measurements necessary for astronomers.
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 stars, the magnetic field is produced from 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.
To confirm their findings and better understand galactic magnetic fields, the team will continue their observations.
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