Westerlund 1-75

Westerlund 1 W75 or Wd 1-75 is a red supergiant (RSG) located in the Westerlund 1 super star cluster. Its radius is calculated to be around 668 solar radii (4.65 × 108 km, 3.10 au). This corresponds to a volume 298 million times bigger than the Sun. If placed at the center of the Solar System, Westerlund 1-75 would engulf the inner limits of the asteroid belt.

The star is classified as a luminous cool supergiant emitting most of its energy in the infrared spectrum. It occupies the upper right corner of the Hertzsprung-Russell diagram. Using the effective temperature of 3,600 K, the bolometric luminosity of 68,000 L ☉ and the solar effective temperature of 5,772 K, the radius of Westerlund 1-75 can be calculated using the Stefan-Boltzmann law at.

Like Westerlund 1-20, Westerlund 1 W26 and Westerlund 1-237, Westerlund 1-75 was observed to be a radio source, however it is weakest along the RSGs in its cluster and remains unresolved at any wavelength.

Westerlund 1-75 is surrounded by extended nebula, although it appears less massive than nebulae around typical red supergiant stars.