Astronomers consider it a ‘record-breaking’ galaxy, since it is the most distant from which a very specific peculiarity has been observed: a strong and organized magnetic field. An unusual feature in galaxies of that age, and that gives important clues about how magnetism is created and evolves in the universe.
It is located five billion light years from Earth, and has a strength and configuration similar to that observed in our own galaxy, the Milky Way, although this, logically, is five billion years younger. Why is your observation so important? Their magnetic activity is proof that galactic magnetic fields are formed in the early life of galaxies , and have remained relatively stable since then. Looking at it is like contemplating the past of our own galaxy, to understand how magnetism has evolved in our own region of the universe.
The finding has been published in the journal Nature Astronomy , and the study leader, an astronomer at the Max Planck Institute for Radio Astronomy, Dr. Sui Ann Mao, calls it “exciting.”
Like all celestial bodies, galaxies have their own magnetic field, but it is incredibly weak – a million times weaker than Earth’s magnetic field. Prior to this research, there was a theory that the magnetic field of a young galaxy starts out weak and entangled, becoming stronger and more organized over time. But this is not what the observation of this distant galaxy tells us.
Image: 5 GHz full intensity radio outline of the gravitational lens system./doi:10.1038/s41550-017-0218-x.
Because the magnetic field of the observed galaxy is not very different from the fields we observe in our Milky Way and nearby galaxies, this detection is evidence that galactic magnetism appears relatively early rather than slowly growing over time, as affirmed this theory.
Faraday rotation detection
Studying the evolution of galactic magnetic fields requires observations of galaxies at different distances from us, that is, of different ages. But these observations are difficult to make, in part because a magnetic field cannot be directly detected. Instead, we can only detect one by observing the magnetic footprint it leaves on the light that passes through it; an effect known as Faraday rotation.
The Max Plank Institute team was able to make the observation because a quasar (a very bright and distant galaxy) was located a little further than the studied galaxy , in the same line of sight. Thanks to this accidental ‘alignment’, the light emitted by the quasar allowed to collect the magnetic fingerprint of Faraday’s rotation , on its way to Earth.
The observation was made using an array of radio telescope antennas on the San Agustin Plains called the Very Large Array , in the New Mexico desert, operated by the National Radio Astronomy Observatory.
“Nobody knows where the cosmic magnetism comes from or how it was generated” , in the words of Professor Bryan Gaensler, co-author of the study. “But now, we have obtained an important clue needed to solve this mystery, by extracting the ‘fossil record’ of magnetism in a galaxy billions of years before today.”
References:
SA Mao, C. Carilli, BM Gaensler, O. Wucknitz, C. Keeton, A. Basu, R. Beck, PP Kronberg & E. Zweibel. ‘Detection of microgauss coherent magnetic fields in a galaxy five billion years ago’. Nature Astronomy (2017). doi: 10.1038 / s41550-017-0218-x
