This extraordinary object is very faint, and remained undiscovered until 2011 when an amateur astronomer captured it in a long-exposure image. It’s composed mostly of doubly ionized oxygen (OIII), formed when high-energy ultraviolet radiation emitted by nearby hot, young stars excites neutral oxygen atoms and sends two of their electrons into higher energy states.
These quantum states are inherently unstable, so over time the electrons spontaneously drop back to lower energy levels, releasing the excess energy as a photon at the characteristic wavelengths of 496 nm and 501 nm, which we see as the blue-green OIII glow. The same phenomenon is visible in the Flying Bat Nebula (Sh2-129) which surrounds the Squid Nebula and glows red with emissions of ionized hydrogen.
Astronomers are still debating the physics behind this nebula’s unique double-lobed shape; some contend it was triggered by a supernova while others believe it’s being driven by energetic outflows from a binary star system in the nebula’s center.
