A Magnetic Field in the Magellanic Bridge

23 May 2017

For the first time, a team of astronomers led by SIfA PhD student Jane Kaczmarek, has detected a magnetic field associated with the Magellanic Bridge, a gaseous structure in the nearby Magellanic Clouds system.

Visible by the naked eyes in the southern night sky, the Large and the Small Magellanic Clouds are two satellites galaxies orbiting our own Galaxy, the Milky Way. These galaxies are the closest pair of satellite galaxies that are not only interacting with our Galaxy, but with one another. Despite being well studied, these galaxies continue to astonish astronomers, revealing the unknown.

The Large Magellanic Cloud and the Small Magellanic Cloud as seen from the Australia Telescope Compact Array at the Paul Wild Observatory in New South Wales, AustraliaCredit:Mike Salway

Using the data from the Australia Telescope Compact Array radio telescope at Paul Wild Observatory in NSW, Jane Kaczmarek and her team were able to make first ever indirect detection of the magnetic field by using distant galaxies that lie behind LMC and SMC.

The radio emission from the distant galaxies served as background `flashlights` that shine through the Bridge, explained Jane Kaczmarek. Its magnetic field then changes the polarisation of the radio signal. How the polarised light is changed tells us about the intervening magnetic field.

This discovery opens new and fascinating questions: was the magnetic field generated from within the Magellanic Bridge? Or was it ripped from the Magellanic Clouds during their interaction with one another?

In general, we do not know how such vast magnetic fields are generated, nor how these large-scale magnetic fields affect galaxy formation and evolution. The LMC and SMC are our nearest neighbours, so understanding how they may help us understand how our Milky Way Galaxy will evolve. Understanding the role that magnetic fields play in the evolution of galaxies and their environment is a fundamental question in astronomy that remains to be answered, says Jane Kaczmarek.

These results are summarised in the paper titled Detection of a coherent magnetic field in the Magellanic Bridge through Faraday rotation published in the Monthly Notices of the Royal Astronomical Society, and it is available on arXiv .