SS Cygni is a special kind of binary system, consisting of a red dwarf star and a white dwarf. According to theoretical models, the white dwarf strips gas from its companion, which leads to periodic outbursts of intense light: a recurrent nova. However, previous observations of the system placed it too far away for those models to work, casting doubt on the theory — a problem for types of systems other than recurrent novas. A new observation using radio telescopes found a much more amenable distance, but led to another problem: why were these two distance measurements so different?

Both used a method known as parallax, a geometrical technique for measuring distances to objects relatively close to the Solar System. The key difference is how the two measurements were calibrated. Parallax doesn’t require knowledge about the emission of light from the object (unlike other distance measurements such as those that use type Ia supernovas), but it still requires reference points. [Read more…]