Although they are roughly 96 ly away, they have one of the highest proper motions of any star in the sky, travelling over 3.5 arcseconds every year.
The stars are believed to originate from outside of the Milky Way, likely from a destroyed, unusually dusty satellite galaxy.
[1][2] They have an extremely low metallicity, only about 3.5% that of the Sun,[2] with unusual chemical abundances very different from those of stars formed anywhere in the galaxy.
It is unknown if HD 134439 and 134440 are actually orbiting each other, as at their distance, they would have to be a minimum 0.14 light-years (8,900 au) apart from each other, which would make them one of the widest binary systems known.
[citation needed] In a 2018 study, it was found that HD 134440 had a noticeably higher metallicity than HD 134439, which could be potentially explained by the star having engulfed a planet orbiting it, suggesting that it may be possible for planets to form even around stars with extremely low content of planet-forming material.