Not “polar” as in “polar bear,” a polar (POE-larr) is the nickname for a kind of star with a high level of polarized light coming from it. In space, light becomes polarized when countless numbers of crystalline dust grains are aligned by strong magnetic fields to face a single direction. Together, they act like a huge cloud of microscopic mirrors and reflect polarized light in a specific proportion. By comparing the amount and orientation of polarized versus unpolarized light, it is possible to determine the configurations of the super-strong magnetic fields around stars that make such a phenomenon possible.

It turns out that polars are binary star systems, usually cataclysmic variables or even low-mass X-ray binaries. The magnetic fields that create the polar phenomenon are millions to billions of times the strength of the Sun’s magnetic field and cause fascinating physical consequences in the binary system.