Powerful forces are at work in the Milky Way’s closest neighbouring galaxy, the Large Magellanic Cloud (LMC). An unknown force is keeping the structure of that galaxy together, despite gravity from the Milky Way tearing it apart.

A team of astronomers, led by Dr Bryan Gaensler head of the Gaensler & Slane (GaS) Research Group at the Harvard-Smithsonian Centre for Astrophysics, used the CSIRO Australia Telescope near Narrabri in NSW to study the galaxy’s magnetic field.

The LMC neighbours the Milky Way at just 160,000 light years away and is joined to the Milky Way by a stream of cold hydrogen gas. According to Gaensler, his team has mapped out the magnetism of the LMC in more detail than any other galaxy. Gaensler’s team was surprised that the LMC’s magnetic field is so smooth and ordered given the internal conflict the galaxy must be experiencing.

“It’s like having a birthday party all afternoon for a bunch of 4-year-olds, and then finding the house still neat and tidy when they leave,” Gaensler says. “Some powerful forces must be at work to keep the magnetic field from being messed up.”

Large spiral galaxies like the Milky Way have gigantic, well-ordered magnetic fields. It is thought that these galaxies manifest a phenomenon known as a “dynamo”. A dynamo is a process where the overall rotation of a galaxy combines and smooths the small magnetic fields created by whirls and eddies of gas. This is similar to the process that produces the earth’s magnetic field.

“But if a galaxy experiences sudden bursts of star formation or supernova explosions, the energy that these processes release should completely disrupt the large-scale magnetic field,” says Lister Staveley-Smith of the CSIRO Australia Telescope National Facility.

“And we know the LMC has had those kind of violent events over the last several thousand million years,” he says. This is part of what makes this new discovery so puzzling.

The researchers have several theories as to what may be keeping the LMC in order. The process they favour is one driven by energetic particles called “cosmic rays”. This would have a much swifter effect than the conventional dynamo mechanism. Like the dynamo mechanism, it requires energetic star formation to operate, so “stars bursting out at random all over would strengthen the magnetic field, not mess it up,” says Gaensler. “You could say this galaxy is thriving on chaos.”