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How the universe got its large magnetic fields remains one of the world’s most difficult open problems astrophysics. Now researchers have proposed a novel solution: a giant “dust battery” that was in operation when the first stars appeared.
Magnetic fields exist everywhere in the universe. Of course there is The Earth’s magnetic fieldthat deflects dangerous cosmic radiation, wobbles our compass and guides flocks of migratory birds. But Other planets and stars have magnetic fieldsalso and the magnetic fields of Jupiter and the Sun are more powerful than those of the earth.
Even the whole thing Milky Way Galaxy has its own magnetic field. It is about a million times fainter than Earth’s, but spans tens of thousands of light-years and spans the entire galaxy. Astronomers know of even larger magnetic fields, some of which fill entire clusters of galaxies that can reach a few million light-years across.
So where do these gigantic magnetic fields come from? Although they are relatively weak, they are incredibly large. So whatever it created must come from suitably high-energy, large-scale sources. Over the decades, astronomers have proposed a number of mechanisms, most of which rely on a dynamo process that takes weak “seed fields” and amplifies them to their present-day values.
Related: The earliest magnetic galaxy ever discovered offers clues to the history of the Milky Way
But that just pushes the goal post further back. Where do the weak seed fields come from?
In one Paper Presented to the Astrophysical Journal in October, the researchers proposed a novel solution. Your scenario begins in cosmic dawnWhen the universe was only a few hundred million years old and the first Stars and galaxies began to shine. After these first stars died, they left behind pieces of heavier elements that found themselves inside each other interstellar space to become the first grains of dust.
These dust grains generally became electrically charged by radiation bombardment and friction between themselves. As the second generation of stars lit up, their intense light shone through all the gas and dust that surrounded them. If these stars were strong enough, their radiation could literally push on the dust grains, causing them to move through the rest of the gas. These moving, electrically charged dust grains would produce a weak but far-reaching electrical current, like a copper wire 1,000 light years above.
Since the radiation filtering by the interstellar gas would not be perfectly uniform, the moving dust grains would tend to clump together in some places and scatter in others. This would create differences in the strength of the electric current from place to place, which would naturally result in a magnetic field due to the laws of electromagnetism.
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In the new study, the researchers found that this magnetic field would be incredibly weak – about a billionth of its strength EarthThe magnetic field. But it would be large enough that other astrophysical processes such as mixing and dynamo amplification could tie into this seed field and produce the magnetic fields we see today.
However, this is just a hypothesis. The researchers concluded their work with a recipe for incorporating this mechanism into simulations Evolution of galaxies and their magnetic fields. This is a crucial step in comparing the full magnetic fields predicted by this theory with those we see in the actual universe. We can’t turn back the clock to see what the universe’s magnetic fields looked like long ago, but we can use ideas like these to try to reconstruct the past.
