Astronomers Measure The Magnetic Field Of A Galaxy 5 Billion Light-Years Away

An international team of astronomers was able to measure the magnetic field of a galaxy 4.6 billion light-years from Earth.

This extraordinary observation was possible thanks to a rare galactic alignment that produced a gravitational lens. The foreground galaxy is massive enough to warp space time and distort the light of a much more distant quasar, splitting its image in two. The quasar light was used to measure the magnetic field of the foreground galaxy.

As reported in Nature Astronomy, the researchers used radio telescopes to study how the magnetic field of the galaxy was affecting the direction in which the photons were oscillating, namely the polarization of light. By measuring the polarization, the team was able to assess the strength of the magnetic field and get a glimpse at its formation.

“The polarization of the waves coming from the background quasar, combined with the fact that the waves producing the two lensed images traveled through different parts of the intervening galaxy, allowed us to learn some important facts about the galaxy’s magnetic field,” lead author, Dr. Sui Ann Mao from the Max Planck Institute for Radio Astronomy, said in a statement.

The study was conducted with the National Science Foundation’s Karl G. Jansky Very Large Array (VLA). Having two images of the same quasars meant that the researchers could measure the magnetic field at opposite sides of the galaxy. Measurements from the two images showed a significant difference between the lensing regions of the galaxy.

Schematic view of the quasar, lensing galaxy, and the VLA. Bill Saxton, NRAO/AUI/NSF; NASA, Hubble Heritage Team, (STScI/AURA), ESA, S. Beckwith (STScI). Additional Processing: Robert Gendler

“The difference tells us that this galaxy has a large-scale, coherent magnetic field, similar to those we see in nearby galaxies in the present-day universe,” Mao added. “The results of our study support the idea that galaxy magnetic fields are generated by a rotating dynamo effect, similar to the process that produces the Sun’s magnetic field.”

This an intriguing finding. Our knowledge of galactic magnetic fields is somewhat limited as they are extremely difficult to measure. Astronomers believe that a dynamo scenario is the most likely but they are keeping their options open.

“There are other processes that might be producing the magnetic fields. To determine which process is at work, we need to go still farther back in time – to more distant galaxies – and make similar measurements of their magnetic fields,” she concluded. The furthest that astronomers have been able to measure magnetic fields is in 36 galaxies, 10 billion light years away from Earth.

Understanding galactic magnetic fields might help us understand better how galaxies evolve over time.  

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