The Bubble Nebula, formally known as NGC 7635, is an H II region and emission nebula in the constellation Cassiopeia. It lies close to the direction of the open cluster Messier 52. The "bubble" is created by the stellar wind from a massive magnitude-8.7 young central star, BD+60°2522 (visible in the centre left of this image). The nebula is near a giant molecular cloud that contains the bubble's expansion while itself being excited by the hot central star, causing it to glow. It was discovered in 1787 by William Herschel. This photograph of the Bubble Nebula was taken by the Hubble Space Telescope in 2016. The image is a composite of separate exposures acquired by the telescope's Wide Field Camera 3; the colours are a result of assigning different hues (blue, green and red) to each monochromatic image associated with an individual filter used to sample a particular wavelength of light.Photograph credit: NASA, ESA, Hubble Heritage Team