The stars pump out a lot of powerful UV energy that ionizes all that hydrogen. Without ionization, the nebula wouldn’t display these colours. But that’s not all the stars are doing.
There’s a lot going on in Dolidze 25, the open cluster in the Smiling Cat nebula’s heart. It’s a stellar nursery, which means some of the gas and dust is being swept up and compressed, triggering the birth of more stars. This is a chaotic process, as if there’s an unquellable storm raging for millions of years.
Our galaxy has a metallicity gradient. Stars nearer the galactic center have higher metallicity than stars near the periphery. The higher metallicity is because they formed from material enriched by previous generations of stars. Since there are more stars being born and dying nearer the galactic center, stars recently born in that region form from material that’s been enriched by the stellar birth/death cycle. But Sh2-284 and Dolidze 25 are located near the.
NASA’s WISE captured this infrared image of Sh2-284. It clearly shows how the stars in Dolidze-25 are carving out a bubble in the middle of the HII region. Image Credit: NASA/JPL-Caltech/UCLA