Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have detected linearly polarized thermal emission from dust grains in 9io9, a strongly lensed, intrinsically luminous galaxy that is forming stars at a rate more than 1,000 times that of the Milky Way at redshift 2.6, within just 2.5 billion years of the Big Bang; this polarized emission arises from the alignment of dust grains with the local magnetic field of 9io9.
This image shows the orientation of the magnetic field in the distant galaxy 9io9, seen here when the Universe was only 20% of its current age — the furthest ever detection of a galaxy’s magnetic field. Image credit: ALMA / ESO / NAOJ / NRAO / Geach et al.
Magnetic fields are fundamental to the evolution of galaxies, playing a key role in the astrophysics of the interstellar medium and star formation.
Large-scale ordered magnetic fields have been mapped in our Milky Way Galaxy and nearby galaxies, but it is not known how early in the Universe such structures formed.
“Many people might not be aware that our entire galaxy and other galaxies are laced with magnetic fields, spanning tens of thousands of light-years,” said University of Hertfordshire’s Professor James Geach.
“We actually know very little about how these fields form, despite their being quite fundamental to how galaxies evolve,” added Stanford University’s Dr. Enrique Lopez Rodriguez.
Using the ALMA data, the astronomers discovered a fully formed magnetic field in the strongly lensed, luminous galaxy 9io9, similar in structure to what is observed in nearby galaxies.
The field is about 1,000 times weaker than the Earth’s magnetic field, but extends over more than 16,000 light-years.
“This discovery gives us new clues as to how galactic-scale magnetic fields are formed,” Professor Geach said.
“Observing a fully developed magnetic field this early in the history of the Universe indicates that magnetic fields spanning entire galaxies can form rapidly while young galaxies are still growing.”
The authors believe that intense star formation in the early Universe could have played a role in accelerating the development of the fields. Moreover, these fields can in turn influence how later generations of stars will form.
“The discovery opens up a new window onto the inner workings of galaxies, because the magnetic fields are linked to the material that is forming new stars,” said ESO astronomer Dr. Rob Ivison.
To make this detection, the researchers searched for light emitted by dust grains in the 9io9 galaxy.
“Galaxies are packed full of dust grains and when a magnetic field is present, the grains tend to align and the light they emit becomes polarized,” they said.
“This means that the light waves oscillate along a preferred direction rather than randomly.”
“When ALMA detected and mapped a polarized signal coming from 9io9, the presence of a magnetic field in a very distant galaxy was confirmed for the first time.”
The findings appear in the journal Nature.
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J.E. Geach et al. Polarized thermal emission from dust in a galaxy at redshift 2.6. Nature, published online September 6, 2023; doi: 10.1038/s41586-023-06346-4
