This Is Why Some Galaxies Have A Green Glow, Even Though There Are No Green Stars
“One of astronomy's biggest surprises came in 2007, when a mysterious green object was found. While sorting through some of the Sloan Digital Sky Survey's 50 million galaxies, citizen scientist Hanny Van Arkel revealed a puzzle. This weird phenomenon, Hanny's Voorwerp, was unlike any other galaxy: distended, irregular, and green. Over the subsequent years, we've discovered perhaps 20 similar objects. This posed a great puzzle for astronomy: no stars are green, so how does this galaxy shine?”
When you take a look at the galaxies out there in the Universe, you fully expect that what you see matches up with the light-emitting stars found inside. This is usually true, but on a few rare occasions, you can see an eerie green glow arising from a few of these distant objects in space. This is puzzling, because there’s no such thing as green stars, nor is there a way to combine various stars to make a green color. (Sorry, combining the light from yellow and blue stars doesn’t make green!)
So how do these green glows come to be? Although it was a mystery when they were first discovered in 2007, astronomers have solved the puzzle. Here’s the resolution.
