How large magnetic fields arise in the universe remains one of the most difficult unsolved problems in astrophysics. Now researchers have proposed a new solution: a giant “dust battery” that would come into play when the first stars appeared. Magnetic fields are everywhere in the universe. Of course, there’s also the Earth’s magnetic field, which deflects dangerous cosmic radiation, moves our compasses, and guides flocks of migratory birds. But other planets and stars also have magnetic fields, and the magnetic fields of Jupiter and the Sun are stronger than Earth’s.

Even the entire Milky Way galaxy has its own magnetic field. It is about a million times fainter than Earth’s, but extends for tens of thousands of light-years and spans the entire galaxy. Astronomers know of even larger magnetic fields that fill entire galaxy clusters, some of which can reach several million light-years across.

So where do these giant magnetic fields come from? Although they are relatively weak, they are incredibly large. So whatever created them must have come from suitable large-scale energy sources. For decades, astronomers have proposed a number of mechanisms, most of which rely on a dynamo process that takes weak “initial” fields and boosts them to present-day values.

But this only moves the goalpost further. Where do poor seed fields come from?

In a paper submitted to the Astrophysical Journal in October, researchers proposed a new solution. Their scenario begins at the dawn of space, when the universe was only a few hundred million years old and the first stars and galaxies were beginning to shine. After these first stars died, they left behind fragments of heavier elements that found each other in interstellar space, becoming the first dust.

These dust particles were often electrically charged as a result of being bombarded with radiation and rubbing against each other. When second-generation stars exploded, their intense light shined through the gas and dust surrounding them. If these stars were powerful enough, their radiation could literally press on dust particles and force them to move through the rest of the gas. These moving electrically charged dust particles create a weak but large-scale electric current, like a copper wire 1,000 light-years across.

Since the filtering of radiation by interstellar gas will not be perfectly uniform, moving dust particles will tend to stick together in some places and disperse in others. This will create a difference in the amount of electric current from place to place and naturally give rise to a magnetic field according to the laws of electromagnetism.

In a new study, researchers found that this magnetic field would be incredibly weak, about one-billionth of the strength of the Earth’s magnetic field. But it could have been large enough for other astrophysical processes, such as mixing and dynamo amplification, to latch onto this initial field and create the magnetic fields we see today.

But this is just a hypothesis. The researchers concluded their work with a recipe for incorporating this mechanism in modeling the evolution of galaxies and their magnetic fields. This is an important step in comparing the total magnetic fields predicted by this theory with what we see in the real universe. We can’t turn back time to see what the universe’s magnetic fields were like long ago, but we can use such ideas to reconstruct the past.