Record-breaking Galaxy Five Billion Light-Years Away Shows We Live in Magnetic Universe

 Image: NRAO/AUI; Bob Tetro

Studying the evolution of galactic magnetic fields requires observations of galaxies at different distances from us because such observations show us galaxies at different ages.

But these observations are difficult to make, in part because a magnetic field can’t be detected directly. Instead, we can only detect one by observing the magnetic fingerprint it leaves on light passing through it—an effect referred to as Faraday Rotation.

Mao, Gaensler and their colleagues were able to make their observation because a quasar—a very bright and distant galaxy—lies beyond the galaxy being studied, along the same line of sight. Thanks to this chance alignment, the quasar’s light passes through the galaxy’s magnetic field on its way to us, picking up the tell-tale Faraday Rotation fingerprint.

The observation was made using the Karl G. Jansky Very Large Array, an array of radio telescope dishes in Plains of San Agustin in the New Mexico desert, operated by the National Radio Astronomy Observatory.

“Nobody knows where cosmic magnetism comes from or how it was generated,” says Gaensler. “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.”

Additional notes:

1) Faraday Rotation: A radio wave, like a wave on a pond, oscillates or vibrates in a single direction or plane; for example, a wave on the surface of a pond move up and down in a vertical plane. When a radio signal passes through a magnetic field, the magnetic field rotates the plane of vibration. This so-called Faraday Rotation gives us information about the strength and the polarity—or direction—of the magnetic field.

2) In the Hubble Space Telescope image, there appear to be three objects. Of the three, the central, dimmer object is the galaxy. Both of the two remaining objects are lensed images of the same, more distant quasar. As light from the quasar travels toward us, its path is bent by the gravity of the galaxy, just as the trajectory of a spacecraft is bent as it flies by a planet. We see light from the quasar that traveled along different paths as multiple images of the same object. Says Mao, “Having multiple lensed images of the background quasar to probe along different sight lines through the lensing galaxy is the key to getting the measurement we have here.”

Contacts and sources:
Prof. Bryan Gaensler, Director
Dunlap Institute for Astronomy & Astrophysics
University of Toronto