Surprise Cloud Around Vast Star.jpg VLT Survey Telescope image of Westerlund 1. This is a false colour optical and near infrared image where nebulosity (hydrogen alpha emission) is highlighted in green. The inset shows the red supergiant W1-26 at the centre with the associated ionised hydrogen "triangular nebula" above and left (with the O9 supergiant W1-25 appearing between the two) appearing green.