Starship Asterisk*

I suspect it still is mostly hydrogen, but that whoever processed the image bumped up the blue filter values help pick out where the oxygen is. True color pictures show a nice red glow, as warm hydrogen gas normally does.

As for where it came from, the presence of oxygen indicates that a massive star, perhaps multiple of them, exploded at some point in the region, spreading its fusion products out into the space around. NGC 6559 probably has a less storied history.

http://antwrp.gsfc.nasa.gov/apod/ap071102.html

The blue false color in the Lagoon Nebula, aka M8, shows that there is an abundance of oxygen in the nebula, compared with the other two nebulae. How is this possible? Where did the oxygen come from? I would think that hydrogen would predominate, like in NGC 6559.