This is the Bubble nebula (NGC7635) located in Cassiopeia. M52 (in the upper left corner) is an open star cluster with approximately 200 members. The ‘bubble’ obvious in this image is a nebula generated by a star over forty times more massive than our own sun. The star is so incredibly hot that it sheds material very quickly, which is then shaped into a bubble by the gas surrounding the star.
The Bubble nebula is located around 7100 light years away from Earth.
Image credit Gerhard Bachmayer