Scientists measure magnetic field around most distant galaxy yet

Galactic magnetism emerges early on in the universe's life


Scientists have measured the magnetic field of a galaxy five billion light years from Earth, the most distant coherent magnetic field that has ever been observed.

An international team of physicists used the Karl G Jansky Very Large Array, a large radio wave observatory in central New Mexico, to study how magnetism manifests in the universe.

The galaxy – codenamed CLASS B1152+199 – has a magnetic field similar in configuration to the Milky Way, but its strength is slightly stronger and on the order of a few microGauss. The results have been published in a paper in Nature on Monday, and they show that galactic magnetic fields take shape early on in a galaxy’s lifetime and remain stable as it evolves.

Measuring the magnetic field of such distant objects is a difficult task, since it cannot be directly detected. Instead, since CLASS B1152+199 is located in front of a quasar, scientists can observe the effects of its magnetic field by analyzing how the quasar’s light is affected as it passes through the galaxy.

The technique is known as Faraday Rotation. The light coming from the quasar is polarized in a certain direction dependent on the galaxy’s magnetic field.

Sui Ann Mao, lead author of the paper and an astronomer at the Max Planck Institute for Radio Astronomy in Germany, said the finding was exciting. “It is now the record holder of the most distant galaxy for which we have this magnetic field information.”

Galaxies have very weak magnetic fields – about a million times weaker than the Earth’s magnetic field.

A previous theory suggested that the magnetic field lines around a young galaxy start off as a weak, tangled mess, becoming stronger and more stable as it ages. But since the new results show that the fields are pretty similar to the ones seen in the Milky Way and other nearby galaxies, it indicates that galactic magnetism emerges early on and does not change much over time.

Bryan Gaensler, co-author of the paper and an astronomer at the University of Toronto, Canada, said: “It 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.”

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

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