Astronomers have discovered the magnetic field of a galaxy so far away that it has taken more than 11 billion years for its light to reach us using the Atacama Large Millimeter/submillimeter Array (ALMA). We see it as it was when the cosmos was only 2.5 billion years old. The outcome gives scientists important hints about how galaxies like our own Milky Way’s magnetic fields formed.
There are many astronomical objects in the universe that contain magnetic fields, including planets, stars, and galaxies. “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,” says James Geach, a professor of astrophysics at the University of Hertfordshire in the United Kingdom and the study’s primary author.
“We actually know very little about how these fields form, despite their being quite fundamental to how galaxies evolve,” adds Enrique Lopez Rodriguez, a researcher at Stanford University in the United States and another study participant. Since astronomers have only so far been able to map the magnetic fields of nearby galaxies, it is unclear how early in the universe’s history and how quickly magnetic fields emerge in galaxies.
Now, Geach and his team have found a completely formed magnetic field in a distant galaxy using ALMA, a project in which the European Southern Observatory (ESO) is a partner. This magnetic field’s structure is comparable to that of neighboring galaxies. Despite being more than 16,000 light-years long, the magnetic field is around 1,000 times weaker than that of Earth.
Geach says, “This finding gives us new hints as to how galactic-scale magnetic fields are formed.” It is possible that magnetic fields covering entire galaxies can arise quickly when newborn galaxies are still expanding based on the observation of a fully established magnetic field at this early stage in the history of the cosmos.
The group speculates that rapid star formation in the early cosmos may have contributed to the acceleration of the fields’ evolution. Furthermore, the formation of future star generations may be affected by these fields. The finding provides “a new window into the inner workings of galaxies, because the magnetic fields are linked to the material that is forming new stars,” according to co-author and ESO astronomer Rob Ivison.
The scientists looked for dust particle-produced light in the far-off galaxy 9io9 in order to make this discovery. Dust grains abound in galaxies, and in the presence of a magnetic field, the grains have a tendency to align and emit polarized light. This indicates that rather than oscillating randomly, light waves now oscillate in a preferred direction. For the first time, the existence of a magnetic field in a very far-off galaxy was proven when ALMA discovered and mapped a polarized signal originating from the galaxy 9io9.
Geach claims that “no other telescope could have accomplished this.” It is hoped that this observation, along with others, will help to shed light on the mystery behind the formation of these basic galactic structures.
The magnetic field of the far-off 9io9 galaxy can be seen in this image, which was captured when the universe was just 20% as old as it is today. This is the furthest a galaxy’s magnetic field has ever been detected. ESO is a partner in the Atacama Large Millimeter/submillimeter Array (ALMA), which was used for the observations. Because the magnetic field of the galaxy and the dust grains in 9io9 are roughly aligned, the dust grains emit polarized light, which causes light waves to oscillate along a chosen path rather than randomly.
Astronomers were able to determine the orientation of the magnetic field from this polarization information, which is represented here as curved lines superimposed on the ALMA image. Astronomers exploited a cunning trick of nature to assist them achieve this finding since the polarized light signal created by the magnetically aligned material in 9io9 was incredibly low, comprising just 1% of the overall brightness of the galaxy.
The fact that 9io9, despite being far away from us, had been amplified by a process known as gravitational lensing was helpful to the scientists. This happens when light from a far-off galaxy, in this example 9io9, is bent by the gravity of a very big object in the foreground, making it look brighter and warped.