Westerlund 1-26 or Wd 1-26 is a red supergiant within the outskirts of the Westerlund 1 super star cluster. It is one of the largest known stars discovered so far although its radius is uncertain but is calculated to be 1,165–1,221 solar radii (810,000,000–849,000,000 km; 5.42–5.68 au), with a possible but very unlikely upper estimate of 2,519 solar radii (1.752×109 km; 11.71 au), corresponding to a volume between 1.58 and 16 billion times bigger than the Sun. Assuming the upper estimate is correct, if placed at the center of the Solar System, its photosphere would engulf the orbit of Jupiter.