THE FORGOTTEN FORCE

A seemingly weak magnetic entity could have made all the difference in our universe’s evolution

- Abigail Beall

Earth is held in its orbit around the Sun, like other planets around their own stars. Stars themselves are held in galaxies by larger, more massive objects like the supermassive black hole at the centre of the Milky Way. The glue that holds galaxies together is the force of gravity. Yet gravity isn’t the only force that matters when it comes to the structure of galaxies and the space between them. For years, interstellar magnetic fields were thought to be so weak they made no difference to how our galaxy evolved. However, research is increasingly showing that magnetic fields in galaxies are important to the way space is shaped.

While the effects of our own planet and star’s magnetic fields can be felt on Earth, the magnetic fields of galaxies are much weaker. In fact, physicists didn’t expect galaxies to have their own magnetic fields until they were first discovered in 1949, when the polarisation of light coming from stars was measured – caused by a magnetic field. The grains of dust in interstellar space are lined up in one direction, like millions of tiny compasses pointing north, creating this polarisation.

Now we know much more about these magnetic fields, but much still remains a mystery. Stretching out in the vast nothingness of space, interstellar magnetic fields can be weaker than fridge magnets, but their effect is very important. There are a few things that make more sense when this tiny effect is taken into account. Even though it’s a small effect, any kind of magnetic field would have an impact on the way charged particles move, therefore altering the shape of the galaxies and the universe.

WEAKER THAN A FRIDGE MAGNET
The magnetic force that permeates interstellar space is surprisingly weak