NGC 6537, Red Spider Nebula

Huge waves are sculpted in this two-lobed nebula some 3000 light-years away in the Sagittarius constellation. This warm planetary nebula harbours one of the hottest stars known and its powerful stellar winds generate waves almost a million million kilometres high. The waves are caused by supersonic shocks, formed when the local gas is compressed and heated in front of the rapidly expanding lobes. The atoms caught in the shock emit the spectacular radiation seen in this image.