When I was young my parents took me to Yellowstone. My most vivid memory of that trip was seeing the Morning Glory Pool. I had never seen water that color before, fiery orange on the outer rim changing to yellow then green and finally to a vibrant teal. and as I stepped closer I was able to see down further into the center, the teal becoming bluer and richer until I got close enough to lean against the safety fence, and saw it…a bright green Mountain Dew can some terrible person tossed into such a wonderful feature of nature.
This is my image of the Ring Nebula (M57). It reminds me of the Morning Glory Pool, but instead of having a Mountain Dew can in the center, it has a white dwarf.
A white dwarf is a planet-sized stellar remnant. Very massive stars explode (and some even implode!) when they run out of fuel but lower mass stars (like our sun) lose their outer layers while the core remains behind cooling very slowly over time. This photo tells that story. You can see the white dwarf in the center and the stellar material that diffused away as the star began to run out of fuel. The colors themselves reveal the chemical composition of the gas. The blue in the center is caused by helium, the greenish-blue inner ring is caused by hydrogen and oxygen and the reddish outer ring is caused by nitrogen and sulfur.