7 Jul 2021

A U of T graduate student has discovered that the largest magnetic fields in the Universe are weaker than a fridge magnet – in fact, about three billion times weaker.

PhD student Ariel Amaral from the Dunlap Institute for Astronomy and Astrophysics and the University of Toronto has led a team of researchers that have helped define the strength of magnetism in the Universe.

Unlocking the mysteries of magnetism is a major key to understanding many astronomical processes – such as the formation of stars, planets, and even galaxies.

Astronomers knew that these magnetic fields should exist based on theory, which Amaral explains was the starting point to the project. Because of their weakness, however, they hadn’t been able to be detected before. “So now we know that the largest magnetic fields must be less than 30nG – which for scale was 3 billion times smaller than a fridge magnet,” she says.

Although the physical size of the magnetic fields studied was immense (about 6 quadrillion times larger than the diameter of the Earth), Amaral says the extent of the magnetism’s weakness was not overly surprising. “Magnetic fields even on Earth are quite weak. If these magnetic fields were much stronger you would be able to notice their effects more – such as in how things are shaped in the Universe.”

Her process was much more hands-on than previous magnetism research. “Prior to this, it’s mostly been theoretical papers that predicted the strengths of magnetic fields,” Amaral explains, “but those fields have never been directly observed or detected.”

Because the fields can’t actually be viewed, Amaral and her colleagues knew they needed to use an indirect method to observe their effects. To do this, they used radio signals. More specifically, they applied a technique called Faraday Rotation, to study the subtle effect magnetic fields have on light. The amount that the light rotates is directly related to the strength of the magnetism at play.

Relatively speaking, astronomers know very little about the Universe’s magnetism, but this may be about to change. “We’re entering an age where we’ll soon have millions of [radio galaxy] sources to perform the same technique that we used,” explains Amaral.

With these sources, astronomers will be able to more precisely measure the properties of magnetism– things like scale, turbulence, and strength.

“We’re really setting the stage here to actually outright detect these magnetic fields. We’ve kind of set up our research so that as new datasets come out, you can use our technique and get results.”

“This will tell us even more about what was going on at earlier times in the Universe.”