Mira B

Mira B (also known as VZ Ceti) is a white dwarf and the companion star to the variable starMira. The two are separated by around 100 AU. Suspected as early as 1918, it was visually confirmed in 1923 by Robert Grant Aitken, and has been observed more or less continually since then, most recently by the Chandra X-Ray Observatory.

Long known to be erratically variable itself, its fluctuations seem to be related to its accretion of matter from Mira's stellar wind, which makes it a symbiotic star.