The Small and Large Magellanic, two of the Milky Way’s closest neighbors, are linked together by a bridge of neutral hydrogen and now, for the first time, astronomers have been able to map the magnetic field streaming through it.
An international team of researchers has used an Australian radio telescope to study the 75,000-light-year gas bridge and measured a magnetic field about a million times weaker than Earth’s own. Their results are published in the Monthly Notices of the Royal Astronomical Society.
The Small and Large Magellanic Clouds (SMC and LMC) are two dwarf galaxies orbiting our galaxy at a distance of 200,000 and 160,000 light-years respectively. Now that the researchers have proved that the magnetic field exists, they hope to understand if it is generated by the galaxies or by the Magellanic Bridge itself.
“There were hints that this magnetic field might exist, but no one had observed it until now,” lead author Jane Kaczmarek, from the University of Sydney, said in a statement.
“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.”
The researchers suggest that as the two galaxies interacted with each other their magnetic fields have been pulled together by the gas that formed the bridge (and a few stars), with a single intergalactic magnetic field across both galaxies.
“In general, we don’t know how such vast magnetic fields are generated, nor how these large-scale magnetic fields affect galaxy formation and evolution,” added Kaczmarek. “The LMC and SMC are our nearest neighbors, so understanding how they evolve may help us understand how our Milky Way Galaxy will evolve.”
Detecting such a weak and distant magnetic field has not been easy. The researchers use the polarization of light to work out the effect of magnetic fields. Polarized light waves oscillate in a single direction, and when they pass through a magnetic field the plane in which they are polarized is rotated. So the team used the Australia Telescope Compact Array radio telescope to study the light from 167 polarized extragalactic radio sources.
“The radio emission from the distant galaxies served as background ‘flashlights’ that shine through the Bridge,” says Kaczmarek. “Its magnetic field then changes the polarization of the radio signal. How the polarized light is changed tells us about the intervening magnetic field.”
More and more galaxies and galactic structures appear to have extended magnetic fields. Astronomers have begun to study them and soon we might see how much of a role they play in the cosmic arena.