A red giant in the constellation Cygnus has swelled so much that its outer layers are spilling onto a small but heavy neighbor — a white dwarf. The gas swirls around the dwarf like water down a bathtub drain, falling onto it. But in CH Cygni, this flow is not calm: every 682.5 seconds, the X-ray emission flares and fades. It's like a lighthouse that rotates and sends out a beam.
This rhythm betrays the white dwarf's magnetic field. Magnetic field lines catch the infalling gas and channel it toward the poles, where it heats up and shines brightly in X-rays. As the dwarf spins, the poles alternately face us — hence the pulsations. CH Cygni was previously suspected of having a magnetic field, but there was no direct evidence. Now there is.
This discovery helps us understand how such pairs live and die. The magnetic field can act like a propeller: it flings some gas away, preventing it from falling onto the dwarf, while also accelerating jets that the system ejects. Perhaps this mechanism explains why CH Cygni brightens and dims. And in the distant future, when the white dwarf accumulates too much matter, it might explode as a Type Ia supernova.
The magnetic field of the white dwarf in CH Cygni is thousands of times stronger than a typical refrigerator magnet, and it forces gas to fall only onto the poles, as if the star wears X-ray 'caps'.
In Arthur C. Clarke's novel 'Rendezvous with Rama,' the protagonists study a mysterious object with an unusual periodicity in its signals — somewhat like the pulsating white dwarf from this news.